Originally posted by poon cho tang:

the sahara, arabian n kalahari deserts shown are not covered by clouds

that's why it's brown

Well, they could have been green.

Göta kanal

Göta Kanal is a Swedish canal constructed in the early 19th century. The canal stretches all the way from Gothenburg on the Swedish west coast, combined with river Göta älv and Trollhätte kanal, through the great lakes Vänern and Vättern, in parallel with Motala ström, and to Söderköping on the Baltic Sea.


Location of Göta Kanal in Sweden

The architect was Baltzar von Platen, working to plans earlier developed at the request of the Swedish king by the British engineer and architect Thomas Telford; he got permission to begin work on April 11, 1810 and the canal was officially opened on September 26, 1832. Telford himself travelled to Sweden in 1810 to oversee some of the initial excavations on the project. Built only decades before the advent of railroads, the canal was soon outdated, and never upgraded. The canal is a tourist attraction, sometimes called the blue ribbon of Sweden.

To support the building of the canal with mechanical works, a small engineering workshop was establihed in Motala called Motala Verkstad. This industry is sometimes called the "Cradle of the Swedish engineering industry".


Flight of Locks on Gota Kanal, Sweden. This flight of locks drops the canal from 88.5 metres above sea level at Motala to 73.2 metres at Lake Boren.

Issue #18

Mariana Trench

The Mariana Trench (or Marianas Trench) is the deepest known submarine trench, and the deepest location in the Earth's crust itself. It is located in the floor of the western North Pacific Ocean, to the east of the Mariana Islands at 11° 21' North latitude and 142° 12' East longitude, which is near Japan. The trench is the boundary where two tectonic plates meet, a subduction zone where the Pacific Plate is being subducted under the Philippine Plate. The bottom of the trench is further below sea level than Mount Everest is above sea level. The trench has a maximum depth of 10,911 m (35,798 feet) below sea level. Taking into account its latitude and the Earth's equatorial bulge, this puts it at 6,366.4 km from the centre of the Earth. The Arctic ocean, on the other hand, is ~4 km deep, which would put its floor at ~6,352.8 km from the Earth's centre, 13.6 km closer.


Mariana Trench on Pacific Ocean map

It was first surveyed in 1951 by the British navy vessel, Challenger II, which gave its name to the deepest part of the trench, the Challenger Deep. Using echo sounding, the Challenger II measured a depth of 5,960 fathoms (10,900 m) at 11° 19' N, 142° 15' E. This sounding was repeatedly made using earphones to hear the return of the signal as the stylus passed across the graduated depth scale, whilst the timing of the speed of the echo-sounding machine, a necessary part of the process, was made with a hand held stopwatch. For these reasons it was considered prudent to subtract one scale division (of 20 fm) when officially reporting a new greatest depth of 5,940 fm (10,863 m) (see link).

In 1957, the Russian vessel Vityaz reported a depth of 11,034 m (36,201 ft), dubbed the Mariana Hollow; this measurement has never been replicated and is not considered accurate. In 1962 the M.V. Spencer F. Baird recorded a greatest depth of 10,915 m (35,810 ft). In 1984 the Japanese sent the Takuyo, a highly specialized survey vessel out to the Mariana Trench and collected data using a narrow, multi-beam echo sounder; they reported a maximum depth of 10,924 m (35,840 ft) (see link) (this is also reported as 10,920±10 m, see link). The most accurate measurement on record was taken by another Japanese probe, Kaiko, on March 24, 1995: 10,911 m (35,798 ft) (see link).

In an unprecedented dive, the U.S. Navy bathyscaphe Trieste reached the bottom at 1:06 pm on January 23, 1960 with U.S. Navy Lt. Don Walsh and Jacques Piccard. Iron shot was used for ballast, with gasoline for buoyancy. The onboard systems indicated a depth of 37,800 ft (11,521 m), but this was later revised to 35,813 ft (10,916 m). At the bottom Walsh and Piccard were surprised to discover soles or flounder about one foot (30 cm) long, as well as shrimp. According to Piccard, "The bottom appeared light and clear, a waste of firm diatomaceous ooze".


January 23, 1960: Just before the dive

At the bottom of the Mariana Trench, water exerts a pressure of 1086 bar (108.6 MPa or 15,751 psi).

Issue #19

Ahaggar Mountains

The Ahaggar Mountains, also known as the Hoggar, are a highland region in central Sahara, southern Algeria. They are located about 1,500 km (932 miles) south of the capital, Algiers and just west of Tamanghasset. The region is largely a rocky desert with an average altitude of more than 900 metres (2,953 feet) above sea level. The highest peak is at 2918 meters (Tahat). A famous and very visited point is the Assekrem, where le Père de Foulcault lived in summer (1905).

Ahaggar Mountains are essentially constituted of volcanic rocks. The climate is very hot in summer and temperatures are below 0°C in winter. Rainfall is rare and sporadic. However, since the climate in less extreme than generally in the Sahara, Ahaggar Mountains is a major location for biodiversity and hosts relicts species. Ahaggar Mountains ecology is best described in the article West Saharan montane xeric woodlands, the ecoregion the area belongs to.

The Ahaggar massif is the land of the Imuhagh, the Tuareg people. In the oasis of Abalassa near the town of Tamanghasset is located the tomb of the famous Tin Hinan, the matriach believed to be the ancestor of the Tuareg of Ahaggar. According to legend, Tin Hinan originated from Tafilalt region in the Atlas mountains. The main city nearby the Ahaggar is Tamanghasset, built in a desert valley or wadi.

Today, the Ahaggar region is a prime tourist destination in Algeria.






Images of the Ahaggar Mountains

Issue #20

Red Sea

The Red Sea is a gulf or basin of the Indian Ocean between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb sound and the Gulf of Aden. In the north is the Sinai Peninsula, the Gulf of Aqaba and the Gulf of Suez (leading to the Suez Canal). The sea is roughly 1,900 km long and at its widest is over 300 km. The sea floor has a maximum depth of 2,500 m in the central median trench and an average depth of 500 m, but it also has extensive shallow shelves, noted for their marine life and corals. The sea has a surface area of roughly 438,000 or 450,000 km². The sea is the habitat of over 1000 invertebrate species and 200 soft and hard corals. The sea occupies a part of the Great Rift Valley.


Conshelf II in the Red Sea, Sudan

Name

The sea was called the "Arabian Gulf" in most European sources up to the 20th century. This was derived from older Greek sources. Herodotus, Straban and Ptolemy all call the waterway "Arabicus Sinus", while reserving the term "Sea of Erythrias" (Red Sea) for the waters around the southern Arabian Peninsula, now known as Indian Ocean.

The name of the sea does not indicate a real red colour, as the seawater is actually blue when viewed afar, and transparent when held in hand. It may signify the seasonal blooms of the red-coloured cyanobacteria Trichodesmium erythraeum near the water surface. Some suggest that it refers to the mineral-rich red mountains nearby, which are indeed called "Mounts of the Edomites" or "the Rubi mountains" in Hebrew language. There is also speculation that the name Red Sea came from a mistranslation of what should have been the Reed Sea.

Physical Properties

Surface water temperatures remain relatively constant at 21-25°C and temperature and visibility remain good to around 200 m, but the sea is known for its strong winds and tricky local currents. The sea was created by the division of Africa from the Arabian peninsula, a movement which began around 30 million years ago. The sea is still widening and there are small volcanic features in the deeper parts, it is considered that the sea will become an ocean in time (as proposed in the model of Tuzo Wilson).

Tourism

The sea is known for its spectacular dive sites such as Ras Mohammed, Elphinstone, The Brothers and Rocky Island in Egypt, and less known sites in Sudan such as Sanganeb, Abington, Angarosh and Shaab Rumi.


The Red Sea in Sudan

The Red Sea was "discovered" as a diving destination by Hans Hass in the 1950s, and by Jacques-Yves Cousteau later.

Bordering Countries

The bordering countries are:

- Northern shore:
-- Egypt
-- Israel
-- Jordan

- Western shore:
-- Sudan
-- Egypt

- Eastern shore:
-- Saudi Arabia
-- Yemen

- Southern shore:
-- Djibouti
-- Eritrea

Towns and Cities

The towns and cities on the Red Sea coast include: Assab, Massawa, Hala'ib, Port Sudan, Port Safaga, Hurghada, El Suweis, Sharm el Sheikh, Eilat, Aqaba, Dahab, Jedda, Al Hudaydah.

Issue #21

Pangæa

Pangæa (Greek for "all lands") is the name Alfred Wegener used to refer to the supercontinent that existed during the Mesozoic era, before the process of plate tectonics separated the component continents. When the continents first came together to form Pangæa about 300 million years ago (mya), mountains were formed, and some of these ranges still exist, such as the Appalachians, the Atlas Mountains, and the Urals. The vast ocean that surrounded Pangæa has been named Panthalassa. Pangæa broke up about 180 mya.


Map of Pangæa

Pangæa was a C-shaped landmass that spread across the equator. The body of water that existed within the "C" has been named the Tethys Sea. Because Pangea was so big, the inland was very dry due to the lack of precipitation. The large continent would have allowed land animals to migrate all the way from the South Pole to the North Pole.

The mantle under Pangæa's former location was still hot and trying to rise upward. As a result, Africa sat several tens of meters higher than the other continents.

Pangæa was probably not the first "supercontinent". It's believed that Pannotia formed about 600 mya and split up 550 mya. Also, Rodinia had formed approximately 1,100 mya and divided 750 mya.

During the Jurassic period, Pangæa broke into two parts: a southern part, Gondwana, and a northern part, Laurasia.

Issue #22

Isthmus of Kra

The Isthmus of Kra is the narrow landbridge which connects the Malay Peninsula with the mainland of Asia. The east part of the landbridge belongs to Thailand, the west part belongs to the Tanintharyi division of Myanmar. To the west of the Isthmus is the Andaman Sea, to the east is the Gulf of Thailand.


The Isthmus of Kra

The narrowest part between the estuary of the Kra river and the bay of Sawi near the city Chumpon has a width of 44 km, and has a maximum altitude of 75 m above sea level. The Isthmus is named after the city Kra Buri, in the Ranong province of Thailand, which is located at the west side of the narrowest part.

The Isthmus of Kra marks the boundary between two parts of the central cordillera, the mountain chain which runs from Tibet through all of the Malay peninsula. The southern part is called the Phuket chain, the northern part is the Tenasserim chain, which continues for 400 km until the Three Pagodas Pass.

Kra Canal

As the Malay Peninsula enlarges the shipping routes around Asia significantly, a canal through the Kra Isthmus was suggested as early as 1677, when the Thai King Narai the Great asked the French engineer de Lamar to survey the possibility of building a waterway to connect Songkhla with Marid (now Myanmar). It turned out to be impractical with the technology of that time. In 1793 the idea resurfaced when the younger brother of King Chakri (Rama I) suggested it to make it easier to protect the western coast with military ships. Also in the early 18th century the British East India Company became interested in a canal. After Burma became a British colony in 1863 with Victoria Point opposite the Kra estuary as its southernmost point, an exploration was undertaken, but again with negative result. In 1882 the constructor of the Suez canal, Ferdinand de Lesseps, visited the area, but wasn't allowed to investigate in detail by the Thai king. In 1897 Thailand and the British empire agreed not to build a canal there, to protect the regional dominance of the harbour of Singapore.

In the 20th century the idea resurfaced several times again, now changing the preferred route to connect the Bandon Bay near Surat Thani with Phangnga. The idea is still entertained by a few Thai politicians today, however the high costs as well as ecological problems make it unlikely to be realized in the near future. Instead currently the construction of a railroad connection between Surat Thani and Phuket is discussed.

In 2005 however, an internal report prepared for Secretary of Defense Donald Rumsfeld was leaked to The Washington Times, spelling out China's strategy of underwriting construction of the $20 billion canal across the Kra Isthmus complete with Chinese port facilities, as part of its string of pearls strategy of forward bases and energy security (see link).

Issue #23

Ninety Mile Beach, New Zealand

Ninety Mile Beach is a beach located on the western coast of the far north of the North Island of New Zealand.

The beach stretches from just north of Kaitaia towards Cape Reinga along the Aupouri Peninsula. It begins close to the headland of Reef Point, to the west of Ahipara Bay, sweeping briefly northwest before turning northeast for the majority of its length. It ends at Scott Point, five kilometres south of Cape Maria van Diemen.


NASA World wind image of Aupouri Peninsula in New Zealand. Ninety Mile Beach, New Zealand is on the west (left) side of the peninsula.

The name Ninety Mile Beach is a misnomer - it is actually 55 miles (88 km) long. The reason for its name is unknown, although several theories have been put forward.

In 1932, Ninety Mile Beach was used as the runway for some of the earliest airmail services between Australia and New Zealand. It is still used as an alternative road to the largely poor quality official route north from Kaitaia.

Issue #24

Loch Ness

Loch Ness (from Gaelic Loch Nis) is a large, deep freshwater lake (known in Scotland as a loch) in the Scottish Highlands, extending for approximately 23 miles (37 km) to the south-west of Inverness. It is the largest body of water in the geological fault line known as the Great Glen, which runs from Inverness in the north to Fort William in the south. The Caledonian Canal, which links the sea at either end of the Great Glen, uses Loch Ness for part of its route.


Location of Loch Ness in Scotland

Loch Ness is one of a series of interconnected, murky lochs in Scotland that were carved by glaciers during previous ice ages. Quite large and deep, Loch Ness has exceptionally low water visibility due to a high peat content in the surrounding soil.

Loch Ness is the second largest Scottish loch by surface area at 56.4 square km (21.8 mile²) but due to its extreme depth is the largest by volume. At its deepest part 226 m (740 ft) London's Telecom Tower at 189 m (620 ft) would be completely submerged.


Urquhart Castle overlooking Loch Ness

Loch Ness is best known for the alleged sightings of the fabled monster, "Nessie", the Loch Ness monster, although it is scenic in its own right. Boat cruises operate from various locations along its shores giving tourists the chance to look for the monster.

It also acts as the lower storage reservoir for the Foyers pumped-storage hydroelectric scheme, which was the first of its kind in Britain. The turbines were originally used to provide power for a nearby mill, but now electricity is generated and supplied to the National Grid.

At its southwestern end, near Fort Augustus, one can see the only island on Loch Ness. Cherry Island is an example of a Crannog (artificial islands generally from the Iron Age).


Fort August Locks, Loch Ness in background

Issue #25

Moraine

Moraine is the general term for debris of all sorts originally transported by glaciers or ice sheets that have since melted away.


Moraine at Mono Lake, California, USA

The following are commonly recognized types of moraine:

-- Lateral moraine: The talus and other material from the sides of a glacial valley accumulated on the glacier and carried along with it. The mass of debris distributed along the lateral edges of the glacier are thus called lateral moraine. In the case of valley glaciers which have disappeared, their former existence may often be proved by the traces of lateral moraines left along the sides of the valley.


Lateral moraine on a glacier joining the Gorner Glacier, Zermatt, Switzerland. The Gorner Glacier runs along the bottom of the picture. The moraine bank runs up the left hand side of the picture and results from rocks and earth falling onto the glacier and from rocks being pulled out by the moving ice. If the glacier then melts a little the moraine bank is left clearly visible.

-- Medial moraine: If one or more tributary glaciers coalesce with the main glacier the lateral moraines unite to form trains of debris on the surface of the glacier at or near its center, called medial moraines.

-- Terminal moraine: When balance is maintained between the melting of a glacier and its forward advance, the debris carried on (superglacial), within (englacial), and dragged along the bottom (subglacial) is dumped at that point and builds up a heterogeneous mass of the transported material called the terminal moraine. If a glacier is slowly retreating and makes successive halts farther and farther up the valley, a series of terminal moraines are formed which are spoken of as recessional moraines.

-- Interlobate moraine: If large glaciers and continental ice sheets advance irregularly so that their margins are lobate, when the margins retreat by melting the resulting terminal moraines of boulders, clay, and sand simulate the original interlobate shape of the glacier or glaciers, and therefore such moraines are called interlobate.

-- Ground moraine: When a valley glacier melts completely away the debris carried on or within it are dropped on the valley floor, forming a deposit called ground moraine. The ground moraine from the melting of the great Pleistocene ice sheets is usually spoken of as till.

Issue #26

Etosha National Park

Etosha National Park in Namibia was first established in 1907, when Namibia was a German colony known as South West Africa. At the time, the park’s original 100,000 km² (38,500 mile²) made it the largest game reserve in the world. Due to political changes since its original establishment, the park is somewhat less than a quarter of its original size, but still remains a very large and significant area in which wildlife is protected.

The Etosha Pan dominates the park. The salt pan desert is roughly 130 km long and as wide as 50 km in places. The salt pan is usually dry, but fills with water briefly in the summer months, when it attracts pelicans and flamingos in particular. Periannual springs attract a variety of game and birds throughout the year, including the endangered Black Rhinoceros and the endemic Black Face Impala.


Satellite picture of the Etosha Pan

In the dry season, winds blowing across the salt pan pick up saline dust and carry it across the country and out over the southern Atlantic. This salt enrichment provides minerals to the soil downwind of the pan on which some wildlife depends, though the salinity also creates challenges to farming and agriculture.

The Etosha Pan was one of several sites throughout southern Africa in the Southern African Regional Science Initiative (SAFARI 2000). Using satellite, aircraft, and ground-based data from sites such as Etosha, partners in this program collected a wide variety of data on aerosols, land cover, and other characteristics of the land and atmosphere to study and understand the interactions between people and the natural environment.

Issue #27

Aswan Dam

Aswan is a city on the first cataract of the Nile in Egypt. Two dams straddle the river at this point: the newer Aswan High Dam, and the older Aswan Dam or Aswan Low Dam.


Aswan Low Dam

Normally, the River Nile floods in the summer every year as waters from Ethiopia flow down the river. These floods brought nutrients and mineral that made the soil around the Nile fertile and ideal for farming. As the population along the river grew there came the need to control the flood waters to protect farmland and cotton fields. In a high-water year, the whole crop may be entirely wiped out, while in a low-water year there was widespread drought and famine.


Map of Egypt showing the location of Aswan and Lake Nasser

Construction history

The British began construction of the first dam in 1899 and it was completed in 1902. A gravity dam, it was 1,900 m long and 54 m high. The initial design was soon found to be inadequate and the height of the dam was raised in two phases, 1907–1912 and 1929–1933.

When the dam almost overflowed in 1946 it was decided that rather than raise the dam a third time a second dam would be built 6 km up-river. Proper planning began in 1952, just after the Nasser revolution, and at first the US was to help finance construction with a loan of USD $270 million. The aid offer was withdrawn in mid-1956 when Egypt formally recognised the People's Republic of China. The Egyptian government intended to continue the project alone and use the revenues of the Suez Canal to help pay for construction. But in the Cold War struggle for influence in Africa the Soviet Union stepped in 1958 and possibly a third of the cost of the dam was paid for as a gift. They also provided technicians and heavy machinery. The enormous rock and clay dam was designed by the Russian Zuk Hydroproject Institute.

Construction began in 1960. The High Dam, El Saad al Aali, was completed on July 21, 1970, with the first stage finished in 1964. The reservoir began filling in 1964 while the dam was still under construction and first reached capacity in 1976. The reservoir raised concerns from archaeologists and a rescue operation was begun in 1960 under UNESCO. Sites were surveyed and excavated and 24 major monuments were moved to safer locations or granted to countries that helped with the works (such as the Debod temple in Madrid).


Aswan High Dam


NASA satellite image of Aswan High Dam

Benefits

The Aswan High Dam is 3,600 m in length, 980 m wide at the base, 40 m wide at the crest and 111 m tall. It contains 43 million m³ of material. At maximum, 11,000 m³ of water can pass through the dam every second. There are further emergency spillways for an extra 5000 m³ per second and the Toshka canal links the reservoir to the Toshka depression. The reservoir, named Lake Nasser, is 480 km long and 16 km at its widest with a surface area of 6,000 km² and holds 150 to 165 km³. It flooded much of lower Nubia and over 90,000 people were displaced. With hydroelectric output of 2.1 gigawatts, the dam holds twelve generators each rated at 175 megawatts. Power generation began in 1967. When the dam first reached peak output it produced around half of Egypt's entire electricity production (about 15% by 1998) and allowed for the connection of most Egyptian villages to electricity for the first time. The effects of dangerous floods in 1964 and 1973 and of threatening droughts in 1972–73 and 1983–84 were mitigated. A new fishing industry has been created around Lake Nasser, though it is struggling due to its distance from any significant markets.


A view from the vantage point in the middle of High Dam towards the "Lotus Flower" tower. This tower was built as an Egyptian-Soviet friendship monument to underline the fact that Soviet Union helped in construction of High Dam.

Environmental issues

In addition to the benefits, however, damming the Nile caused a number of environmental issues. The silt which made the Nile region fertile is instead held at the dam, leading to (expected) silting of the reservoir, which will eventually (an estimated 500 years) render Lake Nasser useless for water storage volume.

There is some erosion of farmland down-river. Erosion of coastline barriers, due to lack of new sediments from floods, will eventually cause loss of the brackish water lake fishery that is currently the largest source of fish for Egypt, and the subsidence of the Nile Delta will lead to inundation of northern portion of the delta with seawater, in areas which are now used for rice crops. The delta itself, no longer renewed by Nile silt has lost much of its fertility. The red-brick construction industry, which used delta mud, is also severely affected. There is significant erosion of coastlines (due to lack of sand, which was once brought by the Nile) all along the eastern Mediterranean.

The need to use artificial fertilizers supplied by international corporations is controversial too, causing chemical pollution which the traditional river silt did not. Indifferent irrigation control has also caused some farmland to be damaged by waterlogging and increased salinity, a problem complicated by the reduced flow of the river, which allows salt water further into the delta. Mediterranean fish stocks are also impacted by the dam. The eastern basin of the Mediterranean is low in fertility, and traditionally the marine ecosystem depended on the rich flow of phosphate and silicates from the Nile outflow. Mediterranean catches decreased by almost half after the dam was constructed, but appear to be recovering. The dam has been implicated in a rise in cases of schistosomiasis (bilharzia), due to the thick plant life that has grown up in Lake Nasser, which hosts the snails who carry the disease.

The construction of the dam also had a major political effect. Lake Nasser is huge, and almost all of Egypt's population lives in the Nile valley. This means that if the dam were to be destroyed, the resulting flood would effectively destroy Egypt completely. It has been rumoured that during the Yom Kippur War the dam – heavily defended by flak – was paint-bombed by Israeli Air Force aircraft, and it has been further suggested that this was a major factor in Anwar Sadat's decision to make peace with Israel at Camp David.


A wall commemorating the completion of Aswan High Dam


A closeup view of the Soviet-Egyptian friendship monument

Issue #28

Hadrian's Wall

Hadrian's Wall (in Latin: Valens Hadriani) was a stone and turf fortification, built by the Romans across the width of Great Britain to prevent military raids by the Pictish tribes of Scotland to the north, to improve economic stability and provide peaceful conditions in the south, to define the frontier physically and to separate the unruly Selgovae tribe in the north from the Brigantes in the south and discourage them from uniting.


Pieces of Hadrian's Wall remain near Greenhead and along the route, though large sections have been dismantled over the years to use the stones for various nearby construction projects.

The name is also sometimes used as a euphemism for the border between Scotland and England, despite its not following the modern border.

The wall was the northern border of the Empire in Britain for most of the Roman Empire's rule, and also the most heavily fortified border in the Empire. In addition to its use as a military fortification, it is thought that the gates through the wall would also have served as customs posts to allow trade to be taxed.

A significant portion of the wall still exists, particularly the mid-section, and for much of its length, the wall can be followed on foot. It is the most popular tourist attraction in Northern England, where it is often known simply as the Roman Wall. It was made a UNESCO World Heritage Site in 1987. English Heritage describes it as "the most important monument built by the Romans in Britain".

Route

Hadrian's Wall ran for 120 km, virtually due west, from Wallsend on the River Tyne to the shore of the Solway Firth. The A69 road follows the course of the wall as it starts in Newcastle-on-Tyne to Carlisle, then on round the northern coast of Cumbria. The wall is entirely in England and south of the border with Scotland by 15 km in the west and 110 km in the east.

Hadrian

Hadrian's Wall was built following a visit by Roman emperor Hadrian. Hadrian was experiencing military difficulties not just in Britain, but from the peoples of various conquered lands across the Empire, including Egypt, Judea, Libya, Mauretania, and many of the peoples conquered by his predecessor Trajan, so was keen to impose order. However the construction of such an impressive wall was probably also built as a symbol of Roman power, both in occupied Britain and in Rome.

Frontiers in the early empire were based more on natural features or fortified zones with a heavy military presence. Military roads or limes often marked the border, with forts and signal towers spread along them and it was not until the reign of Domitian that the first solid frontier was constructed, in Germania Superior, using a simple fence. Hadrian expanded on this idea, redesigning the German border by ordering a continuous timber palisade supported by forts behind it. Although such defences would not have held back any concerted invasion effort, they did physically mark the edge of Roman territory and go some way to providing a degree of control of who crossed the border and where they did it.

Hadrian reduced Roman military presence in the territory of the Brigantes and concentrated on building a more solid linear fortification to the north of them. This was intended to replace the Stanegate road which had previously served as the limes.

Issue #29

Hadrian's Wall - Cont'd

Construction

Construction started in 122 and was largely completed within ten years, with soldiers from all three of the occupying Roman legions participating in the work. The route chosen largely followed the Stanegate road from Carlisle to Corbridge, which was already defended by a limes and several auxiliary forts, including Vindolanda.


The Hadrian's Wall attracts modern tourists.

The initial design appears to have proved unsuitable and it was quickly changed to take a more comprehensive approach, the true complexity of which is still being unravelled. At first, the Stanegate was strengthened through the construction of a ditch and wall with 80 gated milecastle forts every Roman mile and pairs of intermediate turrets used for observation and signaling. Seven forts stood on the route of the limes, with additional ones at either end.

The wall was initially built to a width of 3 metres, but later sections were narrowed to 2.5 metres. The height is estimated to have been around 5 or 6 metres. Along the Wall there were 14 auxiliary forts, including Housesteads and Birdoswald. Local stone was used in the construction of the early wall, except for almost half the route, to the west of Irthing where turf was used instead as there were no useful outcrops nearby. The turf wall was 6 metres wide and around 3.5 m high. Fortlets in this area were also built from timber and earth rather than stone.

The milecastles were of three different designs, depending on which Roman legion built them. The Second, Sixth and Twentieth Legions whose inscriptions tell us were all involved in the construction. Similarly there are three different turret designs along the route. All were about 493 m apart and measured 4.27 m square internally.

Construction was divided into lengths of about 5 miles. One group of each legion would create the foundations and built the milecastles and turrets and then other cohorts would follow, building the wall itself. Sometime during this initial construction however, the plans were changed and was decided to incorporate the larger garrison forts into the wall itself rather than setting them to the south. The eastern end of the wall was extended further east from Pons Aelius (Newcastle) to Wallsend on the Tyne estuary. This length is called the Narrow Wall as it was only 8 Roman feet thick and may have been reduced in size due to the decision to move the garrison forts onto the wall itself.

Some of the larger forts along the wall, such as Chesters and Housesteads were built on top of the footings of milecastles or turrets, showing the change of plan and an inscription mentioning early governor Aulus Platorius Nepos indicates that the change of plans took place early on. In all, 12 large forts were added to the wall, each c. 7.3 Roman miles apart.

Once construction had begun, the Vallum or Fosstum was built on the southern side. It consisted of a large, flat bottomed ditch 6 m wide at the top and 3 m deep bounded by a berm on each side 10 m wide. Beyond the berms were earth banks 6m wide and 2 m high. Causeways crossed the ditch at every fort and at one of the milecastles. Initially the berm appears to have been the main route for transportation along the wall.

The Wall was thus part of a defensive system which, from north to south included:

-- a glacis and a deep ditch armed with rows of pointed stakes
-- the Wall itself
-- a later military road (the "Military Way")
-- the Vallum—two huge banks with a ditch between. The Vallum probably delineated a military zone rather than intending to be a major fortification, though the British tribes to the south were also sometimes a military problem.

Garrison

The wall was garrisoned by a mixture of legionary units and auxiliary units of the army (non-citizens). Their numbers fluctuated throughout the occupation, but may have been around 9,000 strong in general, including infantry and cavalry. The new forts could hold garrisons of 500 men whilst cavalry units of 1000 troops were stationed at either end. The total number of soldiers manning the early wall was probably greater than 10,000.

They suffered serious attacks in 180, and especially between 196 and 197 when the garrison had been seriously weakened, following which major reconstruction had to be carried out under Septimius Severus. After the harsh suppression of the tribes under Septimius, the region near the wall remained peaceful for most of the rest of the 200s. It is thought that many in the garrison may have married and integrated into the local community.

Decline

As the Empire declined, by 400 the garrison had abandoned the wall and it fell into disuse. A large proportion of the stone was reused in other local buildings. This continued until the 20th century.

Other fortifications

The first Roman fortification in Scotland was the Gask Ridge, a series of forts north of the Clyde and Forth estuaries in Perthshire. This was soon abandoned for Hadrian's Wall. Fifteen years after completion of the Hadrian's Wall, a turf fortification, the Antonine Wall, was built to run between the Clyde and Forth. This wall was considerably shorter than Hadrian's Wall, but was manned by roughly the same number of troops. In some ways the Antonine Wall was more sophisticated, including large platforms for ballista. Within one generation the Antonine Wall had been abandoned, and Hadrian's Wall was reoccupied.

Issue #29

Uluru

Uluru (also Ayers Rock or The Rock) is a large rock formation in central Australia, in the Northern Territory. It is located in Uluru-Kata Tjuta National Park, 400 km southwest of Alice Springs - latitude 25° 21' South longitude 131° 05' East. It is the second largest monolith in the world (after Mount Augustus, also in Australia), more than 318 metres (986 ft) high and 8 km (5 mi) around. It also extends 2.5 km (1.5 miles) into the ground. It was described by explorer Ernest Giles in 1872 as "the remarkable pebble".


Uluru at dusk

Uluru is notable for appearing to change colour as the different light strikes it at different times of the day and year, with sunset a particularly remarkable sight. The rock is made of sandstone infused with minerals like feldspar (Arkosic sandstone) that reflect the red light of sunrise and sunset, making it appear to glow. The rock gets its rust color from oxidation.


Uluru, appearing yellow at midday


Uluru, purple in the afternoon

Uluru is sacred to the Aborigines and has many storied springs, waterholes, rock caves and ancient paintings. Ayers Rock was the name given to it by European settlers, after the Premier of South Australia Henry Ayers. Uluru is the name in a local Aboriginal language (Anangu), and since the 1980s has been the officially preferred name, although many people, especially non-Australians, still call it Ayers Rock.


Uluru's location relative to other places in Australia

The Aboriginal community of Mutitjulu (pop. approx. 150) is near the western end of Uluru. From Uluru it is about 21 km to the tourist town of Yulara (pop. 3,000), which is situated just outside of the National Park.

Kata Tjuta, which literally means 'Many Heads' owing to its peculiar formation, is another rock formation about 25 km from Uluru. They are called the Olgas by many Australians. Special viewing areas with road access and ample parking have been constructed in order to give tourists the best views of both sites at dawn and dusk.

In 1980, baby Azaria Chamberlain disappeared while she and her parents were camping near Uluru. Her mother Lindy Chamberlain reported that Azaria had been taken by a dingo, sparking the most publicised trial in Australian history.

On 26 October 1985, the Australian Government returned ownership of Uluru to the local Aboriginal people, the Anangu (or 'people'), of the Pitjantjatjara tribe, who then leased it back to the Government for 99 years as a National Park, even though the government broke two of the promises they had made to them earlier.

Climbing the rock is a popular attraction for a large fraction of the many tourists who visit it each year. A rope handhold makes the climb easier, but it is still quite a long and steep climb and many intended climbers give up partway. There are several deaths a year as a direct result of climbing the rock, mainly from heart failure.


Climbers ignore warning signs at their peril.

The Anangu regard the rock as sacred and would prefer that visitors did not climb it. They have attempted to have climbing banned, but were forced by the government to permit it. They have been reduced to trying to persuade visitors to respect their wishes and not do so. Photography of some particularly sacred portions of Uluru and Katajuta, is prohibited.


Detail of Uluru featuring 'skull' cave.

Issue #30

Delta Works

In the North Sea Flood of 1953, a break in the dikes and seawalls in the Netherlands killed 1,835 people and forced the evacuation of 70,000 more. Ten thousand animals drowned, and 4,500 buildings were destroyed. To prevent such a tragedy from happening again, an ambitious flood defense system was conceived and deployed, called the Delta Works (Dutch: Deltawerken).


Satellite image of the Schelde delta. South part of the Rhine-Meuse-Scheldt delta in the Netherlands, focusing on the Scheldt-influenced bit and showing most of the province of Zeeland. This false colour image was made by NLR and ESA.
The numbers and letters, which have been added afterwards, indicate the following land and water features:

1. The former island of Walcheren
2. The former island of Zuid-Beveland
3. The former island of Noord-Beveland
4. The island of Tholen
5. The former island of Sint-Philipsland
6. The former island of Schouwen-Duiveland
7. Part of the former island of Goeree-Overflakkee (province of South Holland)
8. The mainland, part of the province of North Brabant
9. Part of the region of Zeeuws-Vlaanderen

a. River Scheldt (in Belgium, near Antwerp)
b. The Westerschelde estuary
c. The Braakman bay (now dammed off)
d. The Ghent-Terneuzen Canal
e. The Sloe strait which once separated Walcheren from Zuid-Beveland (now the port area of Flushing)
f. The Veerse Meer (Lake Veere)
g. The Zandkreek strait
h. The Scheldt-Rhine Canal
i. The Oosterschelde estuary, once a branch of River Scheldt
j. The Eendracht, once a branch of River Scheldt, now a section of the Scheldt-Rhine Canal
k. The Keeten-Mastgat strait
l. The Krabbenkreek strait
m. The Krammer strait
n. Lake Grevelingen
o. The North Sea

This project was intended to improve the safety of the lower areas of the Netherlands against severe storms and flooding; since more than one third of the nation's land lies below sea level, this is no simple task. Dunes along the entire seashore were raised by as much as 5 meters, while the islands in Zeeland province were joined together by dams and other large scale constructions to shorten the coastline. The most sophisticated and famous of these dams is the Oosterscheldekering (left of the leftmost "i" on the satellite image), which can be opened and closed to keep the sea at bay while preserving the saltwater river delta for wildlife and the fishing industry.


Oosterscheldekering

The Oosterscheldekering is sometimes referred to as the eighth Wonder of the World, and has been declared one of the modern Seven Wonders of the World by the American Society of Civil Engineers.

However, there is an ongoing fundamental discussion about the basics of the Delta Works: the mainland is subsiding and due to global warming and climate changes, sea levels are rising. Eventually the dikes will have to be made higher and wider, causing even more local subsidence. This is a long term uphill battle against the sea that cannot be won. Some people argue that relocation of population centres and giving up land to the sea would be a longer lasting solution than to 'fight the sea'.

Issue #31

New Madrid Seismic Zone

The New Madrid Seismic Zone, also known as the Reelfoot Rift or the New Madrid Fault Line, is a major seismic zone, located in the mideastern United States. Situated 25 miles below the surface, it could be considered a "failed rift", because it does not split the North American plate.


Seismic map showing the New Madrid Seismic Zone - USGS

The 150-mile long fault system, which extends into five states, stretches southward from Cairo, Illinois, through Hayti-Caruthersville and New Madrid, Missouri, through Blytheville, to Marked Tree, Arkansas. It also covers a part of Tennessee, near Reelfoot Lake, extending southeast into Dyersburg.

Structure

The New Madrid Seismic Zone is made up of reactivated faults that formed when North America began to split or rift apart during the breakup of the supercontinent Rodinia in the Neoproterozoic Era (about 750 million years ago). The rift failed, but remained as a scar or zone of weakness. During the Mesozoic Era (about 200 million years ago), as the Atlantic Ocean was opening in the east, rifting was once again re-activated and intrusive igneous rocks were emplaced. But again the rifting failed and the continent remained intact, although with a significant zone of weakness. This rift is known as the Reelfoot Rift and coincides with the northernmost portion of the Mississippi embayment. Most of the seismicity is located from 5 to 25 km beneath the Earth's surface.

The red zones on the map above indicate the epicenter locations of hundreds of minor earthquakes recorded since the 1970s. Two trends are apparent. First is the general NE-SW trend paralleling the trend of the Reelfoot Rift. The second is the intense cross trend, NW-SE, that occurs just southwest of New Madrid. This second trend coincides with an intrusive igneous body which lies deeply buried beneath the sediments of the rift zone. Several other bodies of deeply buried intrusive rock are known to exist within the seismic zone. The depths of these igneous rock bodies closely corresponds to the depth of the seismic activity.

In New Madrid

The zone is named after the town of New Madrid, Missouri, the site of three of the most severe North American earthquakes in recorded history, including:

- December 16, 1811
- January 23, 1812
- February 7, 1812 was the strongest, with estimated magnitude exceeding 8

In the fault zone

The New Madrid fault zone lies within the central Mississippi River valley, extending from northeast Arkansas, through southeast Missouri, western Tennessee, western Kentucky to southern Illinois. Historically, this area has been the site of some of the largest earthquakes in North America. Between 1811 and 1812, four catastrophic earthquakes, with magnitude estimates greater than 7.0 on the Richter scale, occurred during a 3 month period. Hundreds of aftershocks followed over a period of several years. The largest earthquakes to have occurred since then were on January 4, 1843 and October 31, 1895 with magnitude estimates of 6.0 and 6.2 respectively. In addition to these events, seven events of magnitude >= 5.0 have occurred in the area. Instruments were installed in and around this area in 1974 to closely monitor seismic activity. Since then, more than 4000 earthquakes have been located, most of which are too small to be felt. On average one earthquake per year will be large enough to be felt in the area.

More quakes predicted

The potential for the recurrence of large earthquakes and their impact today on densely populated cities in and around the seismic zone has generated much research devoted to understanding earthquakes. By closely monitoring the earthquake activity, scientists can hope to understand their causes, recurrence rates, ground motion and disaster mitigation. The probability for an earthquake of magnitude 6.0 or greater is significant in the near future, with a 90% chance of such an earthquake by the year 2040.

Historical catastrophes

These catastrophic earthquakes occurred during a three-month period in December 1811 and early 1812. They caused changes in the course of the Mississippi River, which rolled backwards temporarily, and were felt as far away as New York City and Boston, Massachusetts, where churchbells rang. Large areas sank into the earth, fissures opened, lakes permanently drained, new lakes were formed, and forests were destroyed over an area of 150,000 acres (600 km²). Many houses at New Madrid were thrown down. "Houses, gardens, and fields were swallowed up" one source notes. But fatalities and damage were low, because the area was sparsely settled. Hundreds of aftershocks followed over a period of several years.


Earthquakes in the New Madrid seismic zone since 1974. Credit: USGS

All three major quakes are generally believed to have exceeded 8.0 on the Richter Scale, and some seismologists believe the largest was 9.0 or larger. Scientists estimate that there is a 90% probability of a magnitude 6.0 to 7.0 quake on this fault system before 2040. Because of the unconsolidated sediments which are a major part of the underlying geology of the Mississippi embayment, large quakes here can affect as much as 20 times the land area of major quakes on the west coast.

Since 1812

The largest New Madrid seismic zone earthquakes to have occurred since then were on January 4, 1843 and October 31, 1895, with magnitude estimates of 6.0 and 6.2 respectively. The last major earthquake to occur in this region occurred in Charleston, Missouri, in 1895, and is estimated to have had a magnitude of 6.7 on the Richter Scale.


Comparison: the 1895 Charleston, Missouri, earthquake in the New Madrid seismic zone with the 1994 Northridge, California, earthquake. Red indicates area of structural damage, yellow indicates area where shaking was felt.

A request dated January 13th, 1814, by the Territorial Governor, William Clark, asked for Federal relief for the "inhabitants of New Madrid County". This was possibly the first example of a request for disaster relief, which would later become the job of the Federal Emergency Management Agency (FEMA).

Issue #32

Tokyo Tower

Tokyo Tower (Tokyo tawa) is a tower in Minato-ku, Tokyo, Japan, whose design is based on the Eiffel Tower in Paris, France. The Tower is 333 meters tall (9 meters taller than the Eiffel Tower, or 33 meters if the latter's TV Antenna is not included) making it the world's highest self-supporting iron tower.


Tokyo Tower

Unlike the Eiffel Tower, Tokyo Tower is located in the middle of a city block. The tower only weighs about 4,000 tons, which is extremely light compared to the 10,100-ton Eiffel Tower, and it is painted in white and orange according to aviation safety regulations.

In the postwar boom of the 1950s, Japan was looking for a monument to symbolize its ascendancy as a global economic powerhouse. Looking to the Occident for inspiration, the Tokyo Government decided to erect its own Eiffel Tower. It was completed by the Takenaka Corporation in 1958 at a total cost of ¥2.8 billion. At the time it was built it was the tallest structure in Tokyo, but it has since been superceded by several buildings in the Shinjuku and Ikebukuro districts. Although it chiefly functions as a radio and television broadcasting antenna, the Tower is best known as a tourist destination, though it is decried by some as overpriced and inconveniently located, and as having poor amenities.

The first floor houses an aquarium, home to 50,000 fish, the third floor a wax museum and an attraction called the Mysterious Walking World, and the fourth floor a Trick Art Gallery. There are also two observatory floors, the main observatory (at 150 m) and the so-called "special observatory" (at 250 m); both afford a spectacular 360 degree view of Tokyo and, if the weather is clear, Mt. Fuji.



In much the same way the Eiffel Tower has become a cliche in American cinema, the Tokyo Tower is often used in anime and manga, with series such as Digimon, Sailor Moon, Tenchi Muyo!, X, and Magic Knight Rayearth often featuring climatic events occurring at the Tokyo Tower. It has also been used often in the monster films by Toho, having been destroyed by Mothra, Godzilla and also the location of the final battle of King Kong Escapes in which King Kong takes on his mechanical double.

Tokyo Tower is a member of the World Federation of Great Towers.

Address: Nippon Television City Corporation 4-2-8 Shibakoen, Minato-Ku Tokyo, Japan 105-0011

Issue #33

Mammoth Cave National Park

Mammoth Cave National Park is a U.S. National Park in south-central Kentucky, encompassing portions of Mammoth Cave, the most extensive cave system known in the world. The complete name of the cave system is the Flint-Mammoth-Joppa-Toohey Ridge Cave System, named for the ridges under which the caves have formed. It was established as a National park on 1 July 1941. It became a World Heritage Site on 27 October 1981, and an international Biosphere Reserve on 26 September 1990.


Stalagmite formations inside Mammoth Cave, Mammoth Cave National Park

Stephen Bishop, an African-American slave and a guide to the cave during the 1840s and 1850s, was one of the first persons to make extensive maps of the cave. He also named many of the cave's features, describing the cave as "grand, gloomy, and peculiar."

The park's 52,830 acres (214 km²) is located in Edmonson County, Kentucky, with small areas extending eastward into Hart County and Barren County. It is centered around the Green River, with a tributary, the Nolin River, feeding into the Green just inside the park. The Green River is dammed near the western boundary of the park, so that the river only flows freely for a small section in the eastern part of the park.

Almost two million people visit the park every year.

Mammoth Cave is a system in thick limestone strata capped by a layer of sandstone, making the system remarkably stable. It currently comprises over 365 miles of passageway, with new discoveries and connections adding several miles per year to this figure. The cave was a significant source for saltpeter production for the manufacture of gunpowder at one time, especially in the War of 1812.

The sandstone capping layer has collapsed in one area in the southern park, resulting in Cedar Sink, a massive sinkhole that features a small river entering one side and disappearing back underground at the other side.

The caverns of Mammoth Cave National Park are also home to the endangered Kentucky cave shrimp, a sightless albino shrimp found in only three counties of Kentucky.

Park service

The park service offers several cave tours to visitors. Many of the most famous features of the cave, such as Grand Avenue, Frozen Niagra, and Fat Man's Misery, can be seen on lighted tours ranging from one to six hours in length. Two lantern tours, lit only by visitor-carried paraffin lamps, are a popular alternative to the electric lit routes. Several wild tours venture away from the developed parts of the cave into muddy crawls and dusty tunnels.

The Echo River Tour, one of the cave's most famous attractions, used to take visitors on a boat ride along an underground river. The tour was discontinued for logistic and environmental reasons in the early 1990s (see link).

Interested members of the public can join an Earthwatch.org sponsored field survey of the history of Mammoth Cave (see link). However, due to Mammoth Cave park regulations, participation on this project is restricted to US citizens only.

History of the cave

Legend has it that in 1790s a hunter, John Houchin, pursued a wounded bear to a large pit near the Green River and stumbled upon bat-guano clogged entrance.


Map of Mammoth Cave from 1842, penned by Stephen Bishop

The cave was owned by Franklin Gorin by the War of 1812 and the cave was being mined for calcium nitrate (refined from bat guano and converted into the saltpeter, an ingredient of gunpowder). A half interest in the changed hands for ten thousand dollars (a huge sum at the time). After the war when prices fell, the workings were abandoned and it became a minor tourist attraction centering on a native American mummy discovered nearby.

In the early 1900s, Floyd Collins spent ten years exploring the Flint Ridge Cave system before dying in 1925 after he became trapped by falling rocks.

In 1972 a party led by Dr. John P. Wilcox, Patricia Crowther, Richard B. Zopf, Dr. P. Gary Eller, Stephen G. Wells, and Cleveland F. Pinnix (a National Parks Service Ranger) managed to find the narrow crawl which linked the two cave systems. Crowther, a "gung ho caver," and weighing in at 115 pounds, crawled through the narrow canyon, to find the name "Pete H" inscribed on the wall with an arrow pointing in the direction of Mammoth Cave. The name is believed to have been carved by Peter Hanson, who was active in exploring the cave in the 1930's. Hanson was killed in World War II.

The cave is linked with computer games (see interactive fiction); one of the earliest such games, Adventure, is based on parts of the cave system (the Colossal section and the Bedquilt Entrance). The author of the game, Will Crowther, was married to Pat Crowther.

Issue #34

Gulf of Finland

The Gulf of Finland is an arm of the Baltic Sea that extends between Finland (to the north) and Estonia (to the south) all the way to the city of Saint Petersburg in Russia, where the river Neva drains into it. Other major cities around the gulf include Helsinki and Tallinn.


Location of the Gulf of Finland


This Medium Resolution Imaging Spectrometer (MERIS) image is centred over the Gulf of Finland, which extends east between Finland on the north and Estonia on the south and Russia to the west. At the extreme eastern end of the gulf is the Karelian Isthmus, separating it from the Ladoga Lake. The gulf is linked with the Ladoga Lake to the east by the Neva River. To the south, the Narva River links the Gulf of Finland with Lake Peipus. The cities of Helsinki, Finland (top centre left), Tallinn, Estonia (bottom centre left) and Saint Petersburg, Russia are visible as bright areas. Bands 7 (red), 5 (green), and 2 (blue), corresponding to visible light, were used to create this image.

Issue #35

Annapurna

Annapurna is a series of peaks in the Himalayas, a 55-km-long massif whose highest point, Annapurna I, stands at 8,091 m (26,538 ft), making it the 10th-highest summit in the world and one of the "eight-thousanders". Annapurna is a Sanskrit name which is translated as Goddess of the Harvests.


Annapurna I and South from Poon Hill

Elevation: 8,091 metres (26,545 feet), Ranked 10th
Latitude: 28º 35' N
Longitude: 83º 57' E
Location: Nepal
Range: Himalaya
First ascent: 1950 by Maurice Herzog and Louis Lachenal
Easiest route: glacier/snow/ice climb

The Annapurna massif contains six major peaks:
- Annapurna I -- 8,091 m, 26,545 ft.
- Annapurna II -- 7,937 m, 26,040 ft.
- Annapurna III -- 7,555 m, 24,786 ft.
- Annapurna IV -- 7,525 m, 24,688 ft.
- Gangapurna -- 7,455 m, 24,457 ft.
- Annapurna South -- 7,219 m, 23,684 ft.

Annapurna I was the first 8,000 metre peak to be climbed. Maurice Herzog and Louis Lachenal, of a French expedition, reached the summit on June 3, 1950.

The south face of Annapurna was first climbed in 1970 by a British expedition led by Chris Bonnington and including the alpinist Ian Clough, who was killed by a falling ice-pillar during the descent.

On 3 February 1987, Jerzy Kukuczka and Artur Hajzer, a Polish climber, made the first ascent of a eight-thousander in winter.


Annapurna


Annapurna I, South Face. In the foreground is Anatoli Boukreev's memorial shrine, when he died in an avalanche on the south face in 1997.


Annapurna III

Issue #36

Jurassic Coast

The Jurassic Coast is a World Heritage Site in south England. The 95 mile (155km) long site starts at Orcombe Point near Exmouth in East Devon and ends at Old Harry Rocks near Swanage in East Dorset. The site consists of Triassic, Jurassic and Cretaceous cliffs spanning the Mesozoic Era, documenting 180 million years of geological history.


Old Harry Rocks, Dorset, England

The site contains a number of unique geological features and landforms, and shows excellent examples of different landforms, including the natural arch at Durdle Door, as well as the cove and limestone folding at Lulworth. Chesil Beach has fine examples of both tombolos and storm beaches. The site has stretches of both concordant and discordant coastlines. The site is the subject of international field studies because of the quality of the geology and the example of management.


West Bay, Dorset, England

Formation

At the start of the Jurassic period a sea level rose flooding the Triassic landscape. For most of the Jurassic period Dorset was under a tropical sea, and marine life flourished. Sediments accumulated over time, mud in deep parts, sand in shallow parts, forming shale (Kimmeridge), limestone (Lulworth to Portland) and sandstone (Studland). The bodies of dead marine animals, including dinosaurs were preserved in these sediments. A large number of particularly high quality finds were uncovered at Kimmeridge and Lyme Regis. The waters slowly fell and dinosaur footprints have been found embedded in the rocks.

In the cretaceous period the sea level rose again, this laid down more sediments which made the chalk (Old Harry Rocks, White Nothe, behind Lulworth Cove) and clays (between the Limestone and Chalk at Lulworth).


Lulworth Cove, Dorset, England

In places the earth's movement buckled the rock, forming features like the Lulworth Crumple formation. The layout of the rock, and shape of the coast making the concordant and discordant coastlines of the purbecks have led to the formation of features such as Lulworth Cove. Here the limestone has been breached and the soft clays eroded, pockets have formed under the clays where oil has accumulated as the largest onshore oil field in Britain.

Features of interest

- Chesil Beach (tombolo, storm beach)
- Chit Rocks (Stacks, stumps)
- Durdle Door (Natural arch, caves)
- Durlston Country Park
- Isle of Portland
- Kimmeridge (Rocky shore, wave cut platform, fossils)
- Lulworth Cove (Cove, Lulworth crumple)
- Studland Bay (Beach, psammosere)
- The Fleet (saline lagoon behind Chesil Beach)


An ammonite fossil from the western end of Chesil Beach


Durdle Door

Gateway towns

- Abbotsbury
- Bridport
- Budleigh Salterton
- Lulworth
- Lyme Regis
- Sidmouth
- Swanage
- Weymouth

Issue #37

Athabasca Oil Sands

The Athabasca Oil Sands (or "Tar Sands") is a large deposit of tar sands in north-western Canada located mainly in the province of Alberta and, to a much lesser degree Saskatchewan. Oil from tar sands is recovered through various processes including strip mining, separation of oil from tar and sand by steam, and additional refining to convert the molasses-like bitumen into conventional light sweet crude oil.


Athabasca Tar Sands in Alberta

Tar sands oil production has a larger environmental impact and is less efficient compared with conventional crude oil production. In particular, such production makes heavy use of water and causes greater groundwater pollution. As conventional sources of oil are depleted, non conventional sources of oil will increasingly be relied upon to make up the difference. Environmental impacts from tar sands oil fields will grow in direct relation to the expected exponential increase of production over the next 20 years.

Estimated size

It is estimated that the Athabasca Tar Sands field contains 1.3 trillion barrels of oil, of which 300 billion are recoverable with current technology. This is as much as one third of the world's total oil deposits (a similar amount is in the Venezuelan Orinoco tar sands field). Current production at the Athabasca site yields 155,000 barrels of oil per day with an increase to 280,000 by 2010 at a cost of $4,000,000,000 expected. This is still just a fraction of the 82 million barrels of oil produced daily around the world.

According to the Alberta Energy and Utilities Board, the Athabasca tar sands is the largest oil deposit in the world, with an estimated 1.6 trillion barrels (254 km³) of oil, of which at most 315 billion barrels are considered recoverable by the oil companies given current technology. Syncrude, one of the oil companies involved in mining the tar sands, states that the entire tar sand deposit is twice the size of Lake Ontario. It is estimated the Venezuelan Orinoco tar sands deposit is slightly larger than Athabasca.

The Athabasca Tar Sands field is primarily located in and around Fort McMurray, an area that has only recently been heavily explored.

Alberta has huge deposits of oil bearing sands that underlie 140,800 square kilometres (54,363 square miles) of the province. These deposits are separated into three regions: Athabasca (Fort McMurray area), Peace River and Cold Lake on the Saskachewan border.

Issue #38

Tibetan Plateau

The Tibetan Plateau is a large, elevated region in Central Asia, covering much of Tibet. It occupies an area of around 1,000 by 2,500 kilometers, and has an average elevation of over 5,000 meters. Called "the roof of the world," it contains the world's tallest mountain range, the Himalayas, as well as Mount Everest, the world's highest mountain. The plateau was formed by the collision of the Indo-Australian and Eurasian tectonic plates in the Cenozoic period (approximately 55 million years ago), although the process is still ongoing.


NASA satellite image of Tibetan Plateau

The uplift of the plateau is thought to have had a significant effect on climate change, and it is believed to affect the Asian monsoons.

Several of the world's longest rivers have their sources on the Tibetan Plateau:

- Yangtze River (or Chang Jiang)
- Huang He (or Yellow River)
- Indus River
- Ganges River
- Brahmaputra
- Mekong

Between them, these rivers carry 25% of the world's mud.

Issue #39

Eratosthenes

Eratosthenes (276 BC - 194 BC) was a Greek mathematician, geographer and astronomer with (probably) Chaldean origins.


Eratosthenes

He was born in Cyrene (now Shahhat, Libya) and died in Ptolemaic Alexandria. He is noted for devising a system of latitude and longitude and computing the size of the Earth.

Eratosthenes studied at Alexandria and for some years in Athens. In 236 BC he was appointed by Ptolemy III Euergetes I as librarian of the Alexandrian library. He made several important contributions to mathematics and science, and was a good friend to Archimedes. Around 255 BC he invented the armillary sphere, which was widely used until the invention of the orrery in the 18th century.

He calculated the earth's circumference circa 240 BC, using trigonometry and knowledge of the angle of elevation of the Sun at noon in Alexandria and Syene (now Aswan, Egypt). The calculation is based on the assumption that the Earth is spherical and that the Sun is so far away that its rays can be taken as parallel.

Eratosthenes knew that on the summer solstice at local noon on the Tropic of Cancer, the Sun would appear at the zenith, directly overhead- though Syene was in fact slightly north of the tropic. He also knew, from measurement, that in his hometown of Alexandria, the angle of elevation of the Sun would be 7° south of the zenith at the same time. Assuming that Alexandria was due north of Syene- Alexandria is in fact on a more westerly longitude- he concluded that the distance from Alexandria to Syene must be 7/360 of the total circumference of the Earth. The distance between the cities was known from caravan travellings to be about 5,000 stadia. He established a final value of 700 stadia per degree, which implies a circumference of 252,000 stadia. The exact size of the stadion he used is no longer known (the common Attic stadion was about 185 m), but it is generally believed that Eratosthenes' value corresponds to between 39,690 km and 46,620 km. The circumference of the Earth around the poles is now measured at around 40,008 km. Eratosthenes' method was used by Posidonius about 150 years later.

Circa 200 BC Eratosthenes is thought to have coined or to have adopted the word geography, the descriptive study of the Earth.

Eratosthenes' other contributions include:

- The Sieve of Eratosthenes as a way of finding prime numbers.

- The measurement of the Sun-Earth distance, now called the astronomical unit (804,000,000 stadia).

- The measurement of the distance to the Moon (780,000 stadia).

- The measurement of the inclination of the ecliptic with an angle error 7'.

- He compiled a star catalogue containing 675 stars, which was not preserved.

- A map of the Nile's route as far as Khartoum.

- A map of the entire known world, from the British Isles to Ceylon, and from the Caspian Sea to Ethiopia. Only Hipparchus, Strabo, and Ptolemy were able to make more accurate maps in the classical and post classical world.

Eratosthenes was known under the name Beta, because he supposedly proved himself to be the second in the world in many fields. He was also reputedly known for his haughty character. In 195 BC he became blind and a year later he starved himself to death.

Issue #40