~ Mother Earth ~
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Cook Strait
Cook Strait is the strait between the North Island and the South Island of New Zealand. It is named after James Cook who was the first European to sail it. On the north side of the strait is the harbour of Wellington. On the south side are the Marlborough Sounds and Cloudy Bay.
A view of from the summit of Mount Victoria, Wellington - Cook Strait is to the right (west).
The two large bays of Golden Bay and Tasman Bay lie on the South Island coast immediately to the west of the strait, and the North Island coast to the west recedes towards the giant curve of the Kapiti Coast and South Taranaki Bight. To the east of the strait, it is the South Island which recedes, the coast running south-west after reaching the headland of Cape Campbell. The North Island's short south coast stretches along Palliser Bay, terminating at Cape Palliser.
Each island can be seen clearly from the other in good weather. At its narrowest point the Strait is 24 km wide, this being between Cape Terawhiti in the North Island and Perano Head on Arapawa Island in the Marlborough Sounds. Ironically, at this point the South Island's coast is the more northerly.
There are regular ferry services between Picton in the Sounds and Wellington. The sea is often rough due to strong winds, especially from the south.
The Cook Strait ferry Arahura plying the waters of the Marlborough Sounds.
Issue #140 -
Jog Falls
The Jog Falls is the tallest waterfall in India, located in Shimoga District, Karnataka state, southern India. It is created by the river Sharavati, falling through a height of 292 m. The river splits up into four streams just before the waterfall; the four streams are named in accordance with their perceived trajectories:
- Raja (King): Named so because of its apparently 'dignified' and 'serene' fall (first from the left in the picture).
- Rani (Queen), also called Lady: The stream has a winding, twisting trajectory, said to resemble the movements of a female dancer (third from the left in the picture).
- Roarer: This stream appears out of a mass of rocks, making a tremendous amount of noise (hence the name) (second from left, starting from middle height).
- Rocket: Consists of a large volume of water streaming out of a small opening at a very high speed (first from the right).
Jog Falls
Associated with the waterfall is the nearby Linganamakki dam across the Sharavati river, and the hydro-electric power station that it serves. The power station has been operational since 1949, and is, at 1,200 MW capacity, one of the largest hydro-electric stations in India and is a significant source of power for Karnataka. The power station was previously named Krishna Rajendra Hydro-Electric project, after the King of Mysore at the time. The name was later changed to Mahatma Gandhi Hydro-Electric Project. It was served by the Hirebhaskara dam until the 1960s. At this time, a dam across the Sharavati river was built just before the river jumps into the Jog Falls, and this dam has been used for power generation since then.
The dam has led to a reduction of the amount of water reaching the falls during the summer months. During the rainy season (June-October), the floodgates of the dam need to be opened and the waterfall runs full. This is also the main tourist season at the waterfall.
Issue #141 -
Ironbridge Gorge
The Ironbridge Gorge is a deep gorge formed by the river Severn in Shropshire, in England.
The Ironbridge Gorge looking east towards the Iron Bridge that gave the gorge its name.
Originally called the Severn Gorge and sometimes Coalbrookdale, the gorge now takes its name from the village of Ironbridge, which is in turn named after its famous iron bridge, the first of its kind in the world, and a monument to the industry that began there. The bridge was built in 1779 to link the industral town of Broseley with Madeley Wood and Coalbrookdale.
It is a beautiful and scenic place which also has great historical importance: it is said to be the birthplace of the Industrial Revolution. This began in Coalbrookdale with Abraham Darby's invention of a process for producing high quality iron. Other local towns, such as Broseley, Coalport and Jackfield, grew to make the area an industrial centre.
View of the Warfage taken from the centre of the bridge.
The gorge carries the River Severn south towards the Bristol Channel. It was formed during the last ice age when the output from the previously north flowing river became trapped in a lake created by glaciers to the north. The level of the lake rose until it was able to flow over the hills to the south. This flow eroded a path through the hills forming the gorge and permanently diverting the Severn southwards.
There are two reasons the site was so useful to the early industrialists. The raw materials, coal, iron ore, limestone and clay, for the manufacture of iron, tiles and porcelain are exposed or easily mined in the gorge. The deep and wide river allowed easy transport of products to the sea.
Location of Ironbridge Gorge
Issue #142 -
Thousand Islands
The Thousand Islands are a chain of islands that straddle the U.S.-Canada border in the Saint Lawrence River as it emerges from the northeast corner of Lake Ontario. The islands stretch for about 50 mi (80 km) downstream from Kingston, Ontario. The Canadian islands are in the province of Ontario. The U.S. islands are in the State of New York. The islands, which indeed number over a thousand in all, range in size from over a hundred square km to smaller islands occupied by a single residence, to even smaller uninhabited outcroppings of rocks that are home to migratory waterfowl.
The Thousand Islands near Ivy Lea, Ontario
Geologically, the islands are located where a branch of the Canadian Shield runs south across the river to join with the Adirondacks. The islands have long been popular with boaters.
Around twenty of these islands form the St. Lawrence Islands National Park, the smallest of Canada's national parks. The Thousand Islands - Frontenac Arch region was designated a World Biosphere Reserve by UNESCO in 2002. The U.S. islands include numerous New York state parks, including Robert Moses State Park - Thousand Islands, located on an island in the St. Lawrence.
In the late 19th century and early 20th century many distinguished visitors made the region widely known as a summer resort. Several grand hotels provided luxurious accommodations while steamboats offered extensive tours among the islands. Wealthy and middle-class summer residents built summer homes. Some masonry "castles" remain as international landmarks. The most famous extant examples are Singer Castle on Dark Island and the long-neglected but now restored Boldt Castle on Heart Island.
During the half century (1874-1912) of the resort's greatest prominence, most wealthy vacationers came from New York City, joined by prominent families from Chicago, Pittsburgh and other cities of the United States and Canada. The region retains a historically important collection of vacation homes from this time. The Thousand Islands have long been a center for recreational boating. Large steam yachts, many designed by Herreshoff required distinctive yacht houses. The region was known also for innovative power boating during this period. Three local yacht clubs hosted the Gold Cup Races of the American Power Boat Association for nine consecutive years. The Antique Boat Museum at Clayton, NY retains one of the world's major collections of recreational fresh-water boats.
The Thousand Islands Bridge connects New York State and Ontario by traversing Wellesley Island at the northernmost point of US Interstate 81 in Jefferson County and meets Ontario Highway 401.
Panoramic view of several of the Thousand Islands in the Saint Lawrence River, as viewed from New York towards Ontario.
The largest island in the group, Wolfe Island, is located entirely in the Province of Ontario.
The Thousand Islands are not to be confused with the Rivière des Mille-Îles in southwestern Quebec.
The Thousand Islands gave their name to the popular Thousand Island Dressing around the turn of the 20th century when Sophie LaLonde, of Clayton, New York who served the dressing at dinner for guests of her husband, a popular fishing guide, gave the recipe to Clayton hotel owner Ella Bertrand and New York City stage actress May Irwin (who shared it with hotel magnate George C. Boldt).
Issue #143 -
Cabo da Roca
Cabo da Roca (Cape Roca) is a cape that forms the westernmost point of mainland Portugal, and hence the westernmost point of the European mainland. It was known to the Romans as 'Promontorium Magnum'.
The lighthouse on Cabo da Roca
It is located in Lisbon district, 40 kilometres west of Lisbon and 18 kilometres west of Sintra in the Serra de Sintra nature park. Its coordinates, 38°47' N 9°30' W, are inscribed on a stone plaque on the monument at the site. The cliff rises out of the Atlantic Ocean to approximately 140 metres above sea level. On top of it sit a lighthouse and a tourist desk. The cape is a popular tourist attraction.
The stone plaque on the monument
The poet LuÃs de Camões defined Cabo da Roca as the place "where the land ends and the sea begins" (Portuguese: "Onde a terra acaba e o mar começa"). Compare Cape Finisterre (literally End of land) in Spain and Land's End in the United Kingdom.
Issue #144 -
Gateshead Millennium Bridge
The Gateshead Millennium Bridge spans the River Tyne in England between Gateshead on the south bank, and Newcastle upon Tyne on the north bank.
The bridge was lifted into place in one piece by the Asian Hercules II, one of the world's largest floating cranes, on 20 November 2000. It was opened to the public on 17 September 2001. The bridge, which cost £22m to build, was part funded by the Millennium Commission and European Regional Development Fund.
A full view of the Gateshead Millennium Bridge from the Newcastle side
Already acclaimed worldwide for its physical and aesthetic beauty, it has fast become a significant tourist attraction in its own right.
Huge hydraulic rams, one on each side, tilt the bridge back on special pivots to allow small ships and boats to pass underneath. Its appearance during this manoeuvre has led to it being nicknamed the Blinking Eye Bridge.
The bridge operated reliably since construction, opening to allow river traffic to pass as well as 'just for show'. Its reputation was untarnished until October 2004 when the failure of a £200 circuit board prevented the bridge from opening.
The aesthetic of the bridge is sadly marred by piers erected along the watercourse, to guide shipping beneath the highest point of the bridge's span.
Issue #145 -
Lake Titicaca
Lake Titicaca (Spanish: Lago Titicaca), at 3,821 m above sea level, is the highest commercially navigable lake in the world. With a surface area of approximately 8,300 square kilometres Titicaca is South America's largest freshwater lake. The partly-salt Lake Maracaibo in Venezuela is bigger, at about 13,000 square kilometres, but some say it should be classified as a sea because it is connected to the ocean.
Lake Titicaca is South America's largest freshwater lake.
Located in the Altiplano high in the Andes on the border of Peru and Bolivia, Titicaca has an average depth of between 140 and 180 m, and a maximum depth of 280 m. The western part of the lake belongs to the Puno region of Peru, and the eastern side is located in the Bolivian La Paz Department.
More than 25 rivers empty into Titicaca, and the lake has 41 islands – some of which are densely populated.
View of Lake Titicaca shore
Titicaca is notable for a population of people who live on the Uros, nine artificial islands made of floating reeds. These islands have become a major tourist attraction for Peru, drawing excursions from the lakeside city of Puno. Another island, Taquile, is another tourist attraction featuring a different indigenous community. The Taquile locals are known for their handwoven textile products, which are some of the highest quality handicrafts in Peru.
Tourists around Lake Titicaca in a "Reed Boat" ("Caballitos de totora") in Spanish. Each boat lasts about a year or less, and then it gradually becomes waterlogged.
Titicaca is fed by rainfall and meltwater from glaciers on the sierras that abut the Altiplano. It is drained by the Desaguadero River, which flows south through Bolivia to Lake Poopó; however, this effluent accounts for less than five per cent of the water loss, the rest being accounted for by evaporation as a result of the strong winds and intense sunlight at this altitude.
The origin of the name Titicaca is unknown. It has been translated as "Rock Puma", allegedly because of its resemblance to the shape of a puma hunting a rabbit, combining words from the local languages Quechua and Aymara, and as "Crag of Lead". Locally, the lake goes by several names.
Because the southeast quarter of the lake is separated from the main body by the Strait of Tiquina, the Bolivians call this smaller part Lago Huinaymarca and the larger part Lago Chucuito. In Peru, these smaller and larger parts are referred to as Lago Pequeño and Lago Grande, respectively.
Map of Lake Titicaca
Pop-culture references
A segment of the Disney feature Saludos Amigos featured Donald Duck at the water body.
Since portions of its name sound like vulgarities in English slang, Titicaca is the lake that Cornholio, alter-ego of Beavis of MTV's animated series Beavis and Butt-head, claims to come from.
The cartoon Animaniacs featured the lake in a short song segment.
Issue #146 -
Tagus
Tagus (Latin Tagus, Spanish Tajo, Portuguese Tejo) is the largest river on the Iberian Peninsula. It measures 1,038 kilometers in length, 716 km of which are in Spain, 47 km as border between Portugal and Spain and the remaining 275 km in Portugal.
View of Tagus River from Almourol Castle in Portugal.
The source of the Tagus is the Fuente de GarcÃa, in the AlbarracÃn mountains. It ends in the Atlantic Ocean by Lisbon. The largest bridge across the river is Vasco da Gama bridge with a total length of 17.2 km. It is also the largest bridge in Europe.
Apart from Lisbon, the main cities it passes through are Aranjuez, Toledo, Talavera de la Reina and Alcántara in Spain and Santarem and Lisbon in Portugal.
Its delta is partially inverted, and forms a large lagoon.
Issue #147 -
Sinai Peninsula
The Sinai Peninsula (in Arabic, Shibh Jazirat Sina) is a triangle-shaped peninsula lying between the Mediterranean Sea (to the north) and Red Sea (to the south), located in Egypt and has an area of about 60,000 square kilometers. Its land borders are the Suez Canal to the west and the Israel–Egypt border to the north-east. The Sinai Peninsula is in Southwest Asia (also called West Asia - the more geographically accurate term for the Western term of Middle East) while the rest of Egypt is in North Africa.
In this panorama view of the Southeastern Mediterranean (28.0N, 34.0E), the Sinai Peninsula dominates this north looking oblique view. Lying between two great continents, historic Sinai separates Africa from Asia. The Great Rift Fault originates in southern Turkey, through the Jordan River Valley, and the Gulf of Aqaba, the Red Sea and then into east Africa. The atmospheric haze seen throughout is thought to be wind borne atmospheric dust.
The Sinai is almost entirely desert, but is settled along the Sabah coast at Taba (near the Israeli town of Eilat), where there is a hotel and casino. Moving southwards along the coast, there lie: Nuweiba, Dahab and Sharm el-Sheikh. The Sinai is also settled on the north coast near the Gaza Strip at El-Arish.
Mount Sinai in the Sinai is biblically significant as it is allegedly the site where Moses received the Ten Commandments. A monastery situated at St. Catherine in the southern Sinai Peninsula claims to be at the site of Mount Sinai, though historians and archeologists generally reject this as the site.
The eastern boundary of the peninsula is a geological fault zone known as the Great Rift Valley, which can be seen from the upper Jordan River valley, extending southward through the Red Sea into Africa.
History
The Sinai was inhabited by the Monitu and was called Mafkat or Country of Turquoise. From the time of the First dynasty or before, the Egyptians mined turquoise in Sinai at two locations, Wadi Maghareh and Serabit el-Khadim. They were operated on and off on a seasonal basis for thousands of years. Modern attempts to exploit the deposits have been unprofitable. These may be the first known mines.
The Sinai Peninsula, located between Africa and Asia, is a result of those two continents pulling apart from each other. Earth's crust is cracking, stretching, and lowering along the two northern branches of the Red Sea, namely the Gulf of Suez, seen here on the west (left), and the Gulf of Aqaba, seen to the east (right). This color-coded shaded relief image shows the triangular nature of the peninsula, with the coast of the Mediterranean Sea forming the northern side of the triangle. The Suez Canal can be seen as the narrow vertical blue line in the upper left connecting the Red Sea to the Mediterranean.
The peninsula is divided into three distinct parts; the northern region consisting chiefly of sandstone, plains and hills, the central area dominated by the Tih Plateau, and the mountainous southern region where towering peaks abound. Much of the Sinai is deeply dissected by river valleys, or wadis, that eroded during an earlier geologic period and break the surface of the plateau into a series of detached massifs with a few scattered oases.
Two visualization methods were combined to produce the image: shading and color coding of topographic height. The shade image was derived by computing topographic slope in the northwest-southeast direction, so that northwest slopes appear bright and southeast slopes appear dark. Color coding is directly related to topographic height, with green at the lower elevations, rising through yellow and tan, to white at the highest elevations.
Modern history
Until the early 20th century, Sinai was under the control of the Ottoman Empire. In 1906 it became part of then British-controlled Egypt, when the Turkish government yielded to British pressure to hand over the peninsula. The border imposed by the British runs in an almost straight line from Rafah on the Mediterranean shore to Taba on the Gulf of Aqaba. This line served as the eastern border of Sinai ever since, and is now the international border between Israel and Egypt.
In 1948, Egyptian forces passed through Sinai on their way to invade the newly-created state of Israel based on a United Nations mandate dividing the land between the Jews and the Christian and Muslim inhabitants. During the 1948 Arab-Israeli War, Israeli forces entered the north-eastern corner of Sinai, but withdrew shortly after, following British and American pressure. Under the terms of the 1949 Armistice Agreement, Sinai, together with the Gaza Strip, remained under Egyptian control, although parts of it were demilitarized.
In 1956, Egypt used its control of Sinai to impose a blockade on the Israeli port of Eilat. Following this, Israeli forces, aided by Britain and France (which sought to regain control over the Suez Canal) invaded Sinai, and took control over the entire peninsula within several days (see Suez Crisis). Several months later, Israel withdrew its forces from Sinai, following strong American and Russian pressure. Following this, the United Nations Emergency Force, the UNEF, was stationed in Sinai to prevent any military occupation of the Sinai.
In 1967, Egypt reinforced its military presence in Sinai, renewed the blockade on Eilat, and on May 16 ordered the UNEF out of Sinai effective immediately. In the following Six-Day War, the Egyptian army was defeated, and Israel took control over the entire peninsula. The Suez Canal, whose east bank was now controlled by Israel, was closed.
In the 1973 Yom Kippur War, Egyptian forces managed to make advances into the peninsula, but were eventually pushed back across the Suez Canal. As part of the following cease-fire agreements, Israel pulled its forces out of a strip in western Sinai, allowing for the re-opening of the canal.
In 1979 Israel and Egypt signed a Peace Treaty, in which Israel agreed to transfer all control over Sinai to Egypt. Subsequently, Israel pulled out of Sinai in several stages, ending in 1982. The Israeli pull-out involved the destruction of several Israeli settlements including the town of Yamit in north-eastern Sinai.
Present
The Sinai Peninsula is currently divided among several governorates, or provinces, of Egyptian administration. The southern portion of the Sinai is called Janub Sina' in Arabic, literally "Sinai South." The northern portion is named Shamal Sina', or "Sinai North." the other three governates converge on the Suez Canal, including Al Isma'iliyah on its southern end and crosses into Egypt-proper. In the center is As Suways, literally "the Suez;" and Bur Sa'id lies in the north with its capital at Port Said.
Approximately 66,500 live in Janub Sina' and 314,000 live in Shamal Sina'. Port Said itself has a population of roughly 500,000, while the rest of the governorate (Bur Sa'id) itself. Portions of the populations of Al Isma'iliyah and As Suways live in Sinai, while the rest live on the western side of the Suez Canal in Egypt-proper. The combined population of these two governorates is roughly 1.3 million (only a part of that population live in the Sinai, while the rest live on the western side of the Suez).
Issue #148 -
Negev
The Negev (Arabic an-Naqab) is the desert region of southern Israel. In Biblical Hebrew Negev means "south". The Negev covers the greater amount of Israel's official Southern District.
Ruins in the Negev desert, Israel.
Geographically, the over 13,000 km² Negev forms an inverted triangle whose western side is contiguous with the desert of the Sinai peninsula, and whose eastern border is the Wadi Arabah.
Its central city is Beersheba (pop. around 200,000), in the north. The southern end is at the Gulf of Eilat and the resort town of Eilat. Other towns include Dimona and Mitzpe Ramon, and a number of Bedouin towns, including Rahat and Tel Sheva.
The Negev has a number of interesting cultural and geological features. Among these are three enormous, craterlike erosion cirques or machteshim, which are unique to the region: ha-Machtesh ha-Gadol ("The Large Crater"), ha-Machtesh ha-Katan ("The Small Crater") and the Ramon Crater. The last is the biggest of all, in fact - it is probably the largest natural crater on Earth (it was not formed by asteroid impact).
Issue #149 -
Chesapeake Bay
The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Virginia and Maryland. The Chesapeake Bay's watershed covers 64,299 mi² (166,534 km²) in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West Virginia. More than 150 rivers and streams drain into the Bay.
Chesapeake Bay - satellite Landsat photo, circa 2000.
The main stem of the Bay itself is about 189 miles (304 km) long, from the Susquehanna River in the north to the Atlantic Ocean in the south. At its narrowest point (near Annapolis, Maryland, the Bay is 4 miles (6.4 km) wide; at its widest point, near the mouth of the Potomac River, it is 30 miles (48.3 km) wide. Total shoreline for the Bay is 11,684 miles (18,804 km), and the surface area of the Bay and its major tributaries is 4,479 mi² (11,600 km²).
The narrowest point of the Bay is spanned by the Chesapeake Bay Bridge, and the Chesapeake Bay Bridge-Tunnel spans a 23 mile (37 km) section of the Bay at near its mouth.
Geology
The Bay is the drowned valley of the Susquehanna, meaning that was where the river flowed when sea level was lower, but the Bay's geology and its present form and its very location have also been affected by a bolide impact event at the end of the Eocene (about 35.5 million years ago), forming the recently discovered submerged Chesapeake Bay impact crater.
Parts of the Bay, especially the coast line of Calvert County, are lined by cliffs as the result of receding waters millions of years ago. These cliffs, generally known as Calvert Cliffs, are famous for their fossils, especially fossilized shark teeth. Fossilized shark teeth are commonly found washed up on the beaches next to the cliffs. Scientist's Cliffs is a beach community in Calvert County, named so because of the cliffs' propensity for geological finds and numerous fossils.
Much of the bay is quite shallow. A person 6'7" (2 m) tall could not only walk across the mouth of the Susquehanna at the upper bay, but could also traverse some 700,000 acres (2,800 km²) of the bay without being entirely submerged. On average, the depth of the Bay is less than 5 fathoms (30 feet or 9 meters).
History
The Chesapeake Bay was the site of the Battle of the Chesapeake in 1781, during which the French fleet defeated the Royal Navy in the decisive naval battle of the American Revolutionary War.
Today, the Calvert Cliffs Nuclear Generating Station uses water from the Bay to cool its reactor.
The bay is also known for the Chesapeake Bay Retriever, a dog breed developed in this area.
Watershed
The largest rivers flowing into the Bay are:
* Susquehanna River
* Potomac River
* James River
* Appomattox River
* Rappahannock River
* Patuxent River
* Choptank River
* York River formed by:
° Mattaponi River
° Pamunkey River
Fishing Industry
The word Chesepiooc is an Algonquian word meaning "Great Shellfish Bay." The Bay was once known for its great seafood production, especially blue crabs, clams and oysters. The plentiful oyster harvests led to the development of the Skipjack, the State Boat of Maryland, which is the only remaining working boat type in the United States still under sail power. Today, the body of water is less productive than it used to be, because of runoff from development throughout the watershed, urbanization, particularly on its western shore, overharvesting, and invasion of foreign species. The bay though, still yields more fish and shellfish (about 45,000 short tons or 40,000 metric tons yearly) than any other estuary in the United States.
The Bay is famous for its Rockfish, otherwise known as Striped bass. Once on the verge of extinction, Rockfish have made a significant comeback and are now able to be fished in strictly controlled and limited quantities.
The Bay serves as the predominate source of eel in the United States.
In 2005, local governments began debate on the introduction to certain parts of the Bay of a species of asian oyster, to revive the lagging shellfish industry.
The Chesapeake Bay Bridge.
Deteriorating environment conditions
In the 1970s, the Chesapeake Bay contained one of the planet's first identified marine dead zones, where hypoxic waters were so depleted in oxygen they were unable to support life, identified when massive fish kills resulted. Chesapeake Bay's oyster industry has also suffered from two diseases: MSX and dermo. Harmful algae blooms such as Pfiesteria which can effect both fish and humans is also a problem. The depletion of oysters due to overharvesting has had a particularly harmful effect on the quality of the Bay. The reduction of oysters, which serve as natural water filters for the Bay, has led to reduced water quality of the Bay: water that was formerly clear for fathoms is now so turbid that a wader may lose sight of his feet before his knees are wet.
Issue #150 -
Perito Moreno Glacier
The Perito Moreno Glacier (50°29' S 73°03' W) is a glacier located in the Los Glaciares National Park in the south west of Santa Cruz province, Argentina. It is one of the most important tourist attractions in the Argentine Patagonia.
A panoramic view of the Perito Moreno Glacier, Argentina.
The 250 km² ice formation, of 30 km in length, is fed by the continental icefield located in the Andes system shared with Chile; it is one of the world's largest reserves of fresh water.
The glacier advances over the L-shaped "Lago Argentino" ("Argentine Lake") blocking the pass of water when it reaches the opposite shore. Without a escape route, the water-level on the Brazo Rico side of the lake raises up to 30 meters above the level of the other side of the lake. The enormous pressure produced by this mass of waters finally breaks the ice barrier holding it back, in a spectacular rupture of splashing blocks and thunderous sound.
Satellite image of the Glacier. Note the colour difference between both sides of the lake.
The Perito Moreno is around 5 km wide, has an average height of 60 meters, and advances at a speed of 1 to 2 m per day (around 700 m per year), but pieces of it fall at a rate that makes it appear static. Even though the depth at the lake is 170 m, the depth of the glacier 8 km into the mountain is over 700 m. The build-up/break-down cycle of the glacier is not regular and it might take from one year to a more than a decade.
The glacier first ruptured in 1917, taking with him an ancient forest of arrayán trees. The last rupture occurred in March 2004, and previously in 1988, 1984, 1980, 1977, 1975, 1972, 1970, 1966, 1963, 1960, 1956, 1953, 1952, 1947, 1940, 1934 and 1917.
The glacier on the shore 2 weeks before the 2004 rupture.
The Perito Moreno glacier, located 78 km from El Calafate, was named after the explorer Francisco Moreno, a pioneer who studied the region in the 19th century and played a major role in defending the territory of Argentina in the conflict surrounding the international border dispute with Chile.
Piece of the wall falling.
Issue #151 -
Canal du Midi
The Canal du Midi is a 240km long canal in southern France, le midi, linking the Garonne River to the Mediterranean Sea, between Toulouse and the Mediterranean port of Sète, which was created for the canal. The original purpose of the canal was to avoid over 2,000 km trips around hostile Spain between the Atlantic and the Mediterranean Sea (1 month of sailing in the 17th century).
Canal du Midi, Toulouse, France
The canal was opened officially as the Canal Royal de Languedoc on May 24, 1681. It was built under the supervision of Pierre Paul Riquet, a rich tax-farmer who ruined himself in the personal undertaking and died broke in 1680, some months before the canal was opened to navigation. 12,000 workers toiled for fifteen years to create the canal. At Béziers it bridges the river Orb as the pont-canal. The tunnel 173 meters long under a hill at Enserune was the first canal passage ever built through a tunnel.
The Canal du Midi forms, with the Canal Latéral à la Garonne, a waterway (the Canal des Deux Mers) between the Atlantic Ocean and the Mediterranean Sea.
The Canal du Midi has been on the UNESCO's list of World Heritage Sites since 1996.
Issue #152 -
Philippine Trench
The Philippine Trench is a submarine trench to the east of the Philippine islands. It stretches with a length of approximately 1,320 km and a width of round about 30 km from the northeast top of Luzon up to the Indonesian island of Malacca Halmahera. Its deepest point, the Galathea Depth, has a depth of 10,540 meters.
Philippine Trench, to the east of the Philippine islands.
Until 1970, the Philippine Trench was regarded as the deepest point of the earth. Since then, deeper trenches have been discovered, including the Mariana Trench (11,034 meters), the Tonga Trench (10,882 meters) and the Kuril Trench (10,542 meters).
Issue #153 -
Mount McKinley
Mount McKinley or Denali in Alaska is the highest mountain peak in North America, at a height of approximately 6,194 metres (20,320 feet). It is the centerpiece of Denali National Park.
Mount McKinley
Elevation: 6,194 metres (20,320 feet)
Location: Alaska, USA
Range: Alaska Range
Coordinates: 63° 5' 51.34" N 151° 0' 19.86" W
Topo map: USGS Mt. McKinley A-3
First ascent: 1913 expedition led by Hudson Stuck
Easiest route: West Buttress Route
It is commonly known as Denali, which means "the great one" in the Dena'ina language, and which is also the official name currently recognized by the State of Alaska. In 1897 the Mountain was "officially" named Mount McKinley, after the popular U.S. president William McKinley. As the decades progressed Indian-rights activists began to to increasingly view this renaming as colonial and disrespectful. Denali is also the name preferred by the mountain climbing community. There have been several campaigns to officially switch the name of the mountain back to "Denali" nation-wide. However, at the first session of each Congress, Ralph Regula, the congressman from President McKinley's district, introduces legislation "to provide for the retention of the name of Mount McKinley" which effectively blocks any effort at a name change.
A 1903 claim of a first ascent by Dr. Frederick Cook was later proven fraudulent, and the first real ascent came on June 7, 1913 by a party led by Hudson Stuck. In 1947, Barbara Washburn became the first woman to reach the summit. The mountain is regularly climbed today, although it is still a dangerous undertaking, and there have been many fatalities.
Issue #154 -
Barents Sea
The Barents Sea is a part of the Arctic Ocean located north of Norway and Russia. It is named after the Dutch navigator Willem Barents. It is a rather deep shelf sea (average depth 230 m), bordered by the shelf edge towards the Norwegian Sea in the west, the island of Svalbard (Norway) in the north-west, and the islands of Franz Josef Land and Novaya Zemlya (Russia) in the north-east and east.
Southeastern portion of Barents Sea, the Kola Peninsula and the White Sea.
The southern half of the Barents Sea, including the ports of Murmansk (Russia) and Vardø (Norway) remain ice-free year round due to the warm North Atlantic drift. In September, the entire Barents Sea is more or less completely ice-free. Until the Winter War, Finland's territory also reached to the Barents Sea, with the harbor at Petsamo was Finland's only ice-free winter harbor.
There are three main types of water masses in the Barents Sea: Warm, salty Atlantic water (temperature > 3°C, salinity > 35) from the North Atlantic drift, cold Arctic water (temperature < 0°C, salinity < 35) from the north, and warm, but not very salty coastal water (temperature > 3°C, salinity < 34.7). Between the Atlantic and Polar waters, a front called the Polar Front is formed. In the western parts of the sea (close to Bjørnøya), this front is determined by the bottom topography and is therefore relatively sharp and stable from year to year, while in the east (towards Novaya Zemlya), its can be quite diffuse and its position varies a lot between years.
Due to the North Atlantic drift, the Barents Sea has a high biological production compared to other oceans of similar latitude. The spring bloom of phytoplankton can start quite early close to the ice edge, because the fresh water from the melting ice makes up a stable water layer on top of the sea water. The phytoplankton bloom feeds zooplankton such as Calanus finmarchicus, Calanus glacialis, Calanus hyperboreus, Oithona spp., and krill. The zooplankton feeders include young cod, capelin, polar cod, whales and Little Auk. The capelin is a key food for top predators such as the North-East Arctic cod, harp seals, and seabirds such as Common Guillemot and Brunnich's Guillemot. The fisheries of the Barents Sea, in particular the cod fisheries, are of great importance for both Norway and Russia.
Nuclear contamination from dumped Russian naval reactors is an environmental concern in the Barents Sea.
Issue #155 -
Isthmus of Tehuantepec
The Isthmus of Tehuantepec is an isthmus in Mexico. It represents the shortest distance between the Gulf of Mexico and the Pacific Ocean.
The name comes from the town of Tehuantepec (formally, "Santo Domingo Tehuantepec") in Oaxaca state, which in turn comes from the Nahuatl tecuani-tepec, meaning "jaguar hill".
Shaded relief map of Mexico's Isthmus of Tehuantepec. The Isthmus of Tehuantepec is the narrowest part of Mexico between the Atlantic (Gulf of Mexico) and the Pacific oceans. That it is also the flattest has long drawn the interest of would-be canal builders.
The Mexican states of Tabasco and Chiapas stand on the east of the isthmus, with Veracruz and Oaxaca on the west. It includes that part of Mexico lying between the 94th and 96th meridians of West longitude, or the south-eastern parts of Veracruz and Oaxaca, with perhaps small districts of Chiapas and Tabasco. It is 200 km (125 miles) across at its narrowest part from gulf to gulf, or 92 km (120 miles) to the head of Laguna Superior on the Pacific coast. The Sierra Madre breaks down at this point into a broad, plateau-like ridge, whose elevation, at the highest point reached by the Tehuantepec railway (Chivela Pass) is 735 ft. The northern side of the isthmus is swampy and densely covered with jungle, which has been a greater obstacle to railway construction than the grades in crossing the sierra. The whole region is hot and malarial, except the open elevations where the winds from the Pacific render it comparatively cool and healthful. The annual rainfall on the Atlantic or northern slope is 156 in. (Enock) and the maximum temperature about 95 F. in the shade. The Pacific slope has a light rainfall and dryer climate.
North America
The southern edge of North America, if North America is defined as its tectonic plate, lies in the isthmus (this definition would exclude California west of the San Andreas fault, while including areas of eastern Siberia, such as Kamchatka), and not at the Isthmus of Panama.
Proposed canal
Since the days of Hernán Cortés, the Tehuantepec isthmus has been considered a favorable route, first for an interoceanic canal, and since the 19th century for an interoceanic railway. Its proximity to the axis of international trade gives it some advantage over the Panama route; the Isthmus of Panama, however, is significantly narrower, making for a shorter traversal. See also: Panama Canal, Nicaragua Canal.
Railway
When the great cost of a canal across the isthmus compelled engineers and capitalists to give it up as impracticable, James B. Eads proposed to construct a quadruple track ship-railway, and the scheme received serious attention for some time. Then came projects for an ordinary railway, and several concessions were granted by the Mexican government for this purpose from 1857 to 1882. In the last-named year the Mexican government resolved to undertake the enterprise on its own account, and entered into contracts with a prominent Mexican contractor for the work. In 1888 this contract was rescinded, after 108 km (67 mi) of road had been completed. The next contract was fruitless because of the death of the contractor, and the third failed to complete the work within the sum specified (2,700,000). This was in 1893, and 60 km (37 mi) remained to be built. A fourth contract resulted in the completion of the line from coast to coast in 1894, when it was found that the terminal ports were deficient in facilities and the road too light for heavy traffic. The government then entered into a contract with the London firm of contractors of S. Pearson & Son, Ltd., who had constructed the drainage works of the valley of Mexico and the new port works of Veracruz, to rebuild the line and construct terminal ports at Coatzacoalcos on the Gulf coast, and at Salina Cruz on the Pacific side. The work was done for account of the Mexican government. Work began on 10 December 1899, and was finished to a point where its formal opening for traffic was possible in January 1907.
The railway is 308 km (192 mi) long, with a branch of 29 km (18 mi) between Juile and San Juan Evangelista. The minimum depth at low water in both ports is 33 ft., and an extensive system of quays and railway tracks at both terminals affords ample facilities for the expeditious handling of heavy cargoes. The general offices, shops and hospital are located at Rincón Antonio, at the entrance to the Chivela Pass, where the temperature is cool and healthful conditions prevail. At Santa Lucrecia, 175 km (109 mi) from Salina Cruz, connection is made with the Veracruz & Pacific railway (a government line), 343 km (213 mi) to Córdoba, Veracruz, and 500 km (311 mi) to Mexico City.
Issue #156 -
Bondi Beach
Bondi Beach (with a long i) is a hugely popular beach and suburb of Sydney, Australia. It is situated in the Eastern Suburbs, several kilometres from the centre of the city. Large numbers of tourists visit Bondi Beach throughout the year and many British tourists spend Christmas Day there.
Bondi Beach, Sydney, Australia.
Surf LifeSaving Australia has given different hazard ratings to Bondi Beach as at 2004. While the northern end has been rated a gentle 4, the southern side is rated as a 7 (with 10 as the most hazardous) due to a famous rip current known as the "Backpackers Express" (also known as "Bronte Express" because you would supposedly end up at Bronte - two beaches south - if caught in it). In actual fact there are up to five rip currents operating along the beach, the Backpackers' Express being the one closest to the designated swimming area. The beach has an underwater shark net in place sporadically during the swimming season. It is removed for repairs in the winter and is redeployed again in the summer.
Bondi Beach hosted the beach volleyball competition at the 2000 Summer Olympics. Bondi Beach is the end point of the City to Surf Fun Run. The run is held each year in August. Until the mid 1990s the run was held in October, late autumn, until the number of heat-related deaths forced organisers to rethink the event. The race attracts over 60,000 entrants who complete the 14 km run from the central business district of Sydney to Bondi Beach.
History
Bondi Beach was a working class suburb throughout most of the twentieth century. Bondi Beach and the Eastern Suburbs also became home for many mainly Jewish migrants as people fled war and the Holocaust from Poland and Germany. This can be noted by the synagogues and the kosher businesses in the area.
During the 1970s and 80s it was renowned for its immigrant New Zealander population. The Bondi Astra hotel, now an apartment complex, was notorious as a place to buy illegal late-night liquor and heroin. A major factor in Bondi's seedy image was the fact that Sydney's Water Board maintained an untreated sewage outlet at the north end of the beach, resulting in the term 'Bondi Cigar' - a somewhat exaggerated reference to human faeces floating in on the tide. The sewage outlet was closed in the mid 1990s when a deep water ocean outfall was built.
In recent decades Bondi has become gentrified and is home to many famous Australians such as media baron James Packer. War correspondent, film-maker and playwright John Pilger was born in Bondi Beach.
Origin of term
Bondi, derived from an old Aboriginal term meaning, approximately, "sound of water breaking on the beach".
Issue #157 -
Vanadinite
Vanadinite is a mineral with the formula Pb5(VO4)3Cl, lead chlorovanadate. It is part of a series with two other minerals: pyromorphite (Pb5(PO4)3Cl) and mimetite (Pb5(AsO4)3Cl).
Vanadinite from the Pure Potential Mine, La Paz County, Arizona, USA. Vivid orangy-red lustrous hexagonal vanadinite crystals, which measure up to 5 mm (0.2") in length.
It has hexagonal crystals, usually prismatic but the crystals are often skeletal or cavernous and it may be found in crusts. It is brittle and has an uneven fracture. The hardness of vanadinite is 2.75-3 and its specific gravity is 6.7-7.2. It has a resinous lustre and is coloured yellow, yellowish-brown, reddish-brown or red. It is translucent or opaque.
Vanadinite from Mibladen, Morocco. Hexagonal reddish-brown vanadinite crystals, which measure up to 6 mm across (0.2").
Vanadinite is not a common mineral, occurring as an alteration product in lead deposits. It is found in the Ural Mountains, Austria, Spain, Scotland, the Transvaal, Morocco, Argentina, Mexico and in the United States states: Arizona, New Mexico and South Dakota. It is used as an ore of vanadium and to some extent of lead as well. The mineral was first described as a chromate when it was discovered by Andrés Manuel del RÃo in Mexico in 1801, as the metal vanadium was not itself discovered until 1830.
Issue #158 -
Afsluitdijk
The Afsluitdijk (Closure-dike) is a major dam in the Netherlands, constructed between 1927 and 1933 and running from Den Oever on Wieringen in North Holland province, to the village of Zurich (mun. Wûnseradiel) in Fryslân province, over a length of 32 km and a width of 90 m, at an initial height of 7.25 m above sea-level. It is a fundamental part of the larger Zuiderzee Works, damming off the Zuiderzee, a salt water inlet of the North Sea and turning it into the fresh water lake of the IJsselmeer.
Afsluitdijk, the Netherlands. On the left side is the sea, and on the right side the lake (IJsselmeer) created by the Afsluitdijk.
Previous experiences had demonstrated that till (boulder clay), rather than just sand or clay, was the best primary material for a structure like the Afsluitdijk, with the added benefit that till was in plentiful supply in the area; it could be retrieved in large quantities by simply dredging it from the bottom of the Zuiderzee. Work started at four points: on both sides of the mainland and on two specially made construction-islands (Kornwerderzand and Breezand) along the line of the future dike.
From these points the dike slowly grew by ships depositing till into the open sea in two parallel lines. Sand was then poured in between the two dams and as it emerged above the surface was then covered by another layer of till. The nascent dike was then strengthened from land by basalt rocks and mats of willow switch at its base. The dike could then be finished off by raising it further with sand and finally clay for the surface of the dike, on which grass was planted.
Construction progressed better than expected; at three points along the line of the dike there were deeper underwater trenches where the tidal current was much stronger than elsewhere. These had been considered to be major obstacles to completing the dike, but all of them proved to be relatively straightforward. On May 28, 1932, two years earlier than initially thought, the Zuiderzee ceased to be as the last tidal trench of the Vlieter was closed by a final bucket of till. The IJsselmeer was born, even though it was still salty at the time.
The dike itself however was not finished yet as it still needed to be brought up to its required height and a road linking Friesland and North Holland (the current A7/E22 motorway) also remained to be built. It would not be until September 25, 1933, that the Afsluitdijk was officially opened, with a monument marking the spot where the dike had been closed. The amount of material used is estimated at 23 million m³ of sand and 13.5 million m³ of till and over the years an average of around 4,000 to 5,000 workers were involved with the construction every day, relieving some of the unemployment following the Great Depression.
Beside the dam itself there was also the necessary construction of two complexes of shipping locks and discharge sluices at both ends of the dike. The complex at Den Oever includes the Stevin lock (named after mathematician and engineer Simon Stevin) and three series of five sluices for discharging the IJsselmeer into the Wadden Sea; the other complex at Kornwerderzand is composed of the Lorentz locks (named after Hendrik Lorentz, the famous physicist, who personally did the calculations of the tides that were crucial to the construction of the afsluitdijk) and two series of five sluices, making a total of 25 discharge sluices. Periodically discharging the lake is necessary since it is continually fed by rivers and streams (most notably the IJssel river that gives its name to the lake) and polders draining their water into the IJsselmeer.
Issue #159 -
Levee
A levee (from the French for "raised") is a natural or artificial embankment or dyke, usually earthen, which parallels the course of a river. The word seems to have come into English through its use in colonial Louisiana.
Artificial Levees
Artificial levees function to prevent flooding of the adjoining countryside; however, it also confines the flow of the river resulting in higher and faster water flow.
Levees are usually built by piling earth on a cleared, level surface. Broad at the base, they taper to a level top, where temporary embankments or sandbags can be placed. Because flood discharge intensity increases in levees on both banks, and because silt deposits raise the level of riverbeds, planning, as well as auxiliary measures are vital.
Prominent levee systems exist along the Mississippi River and Sacramento Rivers in the United States, and the Po, Vistula, and Danube in Europe.
In some countries, levees are known by other names, such as floodbanks or stopbanks.
Levees keep high water on the Mississippi River from flooding Gretna, Louisiana in March, 2005.
Levees in Popular Culture
The song "I've Been Working On the Railroad" was, according to Carl Sandburg, originally "I've Been Working On the Levee" before the days of railroads. Other notable mention of levees in music are Led Zeppelin's cover version of a Memphis Minnie track When the Levee Breaks, and then A Perfect Circle's cover of the same song. Don McLean mentions driving his "Chevy to the Levee" in his song "American Pie".
Natural Levees
A natural levee results from the deposit of material by a river during flood stage resulting in the land near a river being raised in elevation. When the river is not in flood state it cuts a channel in the elevated material. Natural levees are especially noted on the Yellow River in China near the sea where ocean going ships appear to sail high above the plain on the elevated river. Natural levees are also present on the Rio Grande River in Colorado's San Luis Valley.
Natural levees are formed as sediment of larger grain size settles out on the banks of channels owing to the drop in flow velocity on the edge of the channel.
Levees in Tidal Waters
The same basic process occurs in tidal creeks when the incomming tide carries mineral material of all grades up to the limit imposed by the energy of the flow. As the tide overflows the sides of the creek towards high water, the flow rate at the brink slows and larger sediment is deposited, forming the levee. At the height of the tide, the water stands on the salt-marsh or flats and the finer particles slowly settle, forming clay. In the early ebb, the water level in the creek falls leaving the broad expanse of water standing on the marsh at a higher level.
The area of water on the marsh is much greater than the water surface of the creek so that in the latter, the flow rate is much greater. It is this rush of water, perhaps an hour after high water, which keeps the creek channel open. The cross-sectional area of the water body in the creek is small compared with that initially over the levee which at this stage is acting as a weir. The deposited sediment (coarse on the levee and fine on the mud flats or salt-marsh) therefore tends to stay put so that, tide by tide, the marsh and levee grow higher until they are of such a hight that few tides overflow them. In an active system, the levee is always higher than the marsh. That is how it came to be called "une rive levée" or raised shore.
Issue #160 -
Communards' Wall
The Communards’ Wall (French: Mur des Fédérés) at the Père Lachaise cemetery is where, on May 28, 1871, one-hundred forty-seven fédérés, combatants of the Paris Commune, were shot and thrown in an open trench at the foot of the wall. To the French left, especially socialists and communists, the wall became the symbol of the people’s struggle for their liberty and ideals. Many leaders of the French Communist Party, especially those involved in the French resistance, are buried nearby.
Communards' Wall at the Père Lachaise cemetery in Paris
The Père Lachaise cemetery was established in May of 1804 on a land owned by the Jesuits for centuries, and where Père ("Father") Lachaise, confessor of Louis XIV, lived the latter part of his life. Cemetery of the aristocracy in the 19th century, it also received the remains of famous people from previous eras. During the spring of 1871 the last of the combatants of the Commune entrenched themselves in the cemetery. The Armée versaillaise, which was summoned to suppress the Commune, had control over the area towards the end of the afternoon of May 28, and shot all of the prisoners against the wall.
The massacre of the Communards did not put an end to the repression. During the fighting between 20,000 and 35,000 deaths, and more than 43,000 prisoners were taken; afterwards, a military court pronounced about a hundred death sentences, more than 13,000 prison sentences, and close to 4,000 deportations to New Caledonia.
Monument in memory of the Communards shot at the Communards' Wall, in the Samuel de Champlain's square near the Père Lachaise cemetery in Paris, built with the original stones from the Communards' Wall.
The memory of the Commune remained engraved in the people's memory, especially within the Workers' Movement which regenerated itself in a few years time. The first march before the Wall, at the call of Jules Guesde, took place in May 23, 1880, two months before the Communards' Amnesty: 25,000 people, a symbolic "immortal" red rose in their buttonholes, stood up against police forces. From that time on, this "ascent to the Wall", punctuated French labor force political history. Every year since 1880, the organizations of the French left have held a demonstration in this symbolic place during the last week of May. Jean Jaurès -- although a child in the provinces at the time of the Commune, hence with no direct memory -- made the ascent several times, accompanied by Edouard Vaillant, Jean Allemane, and by thousands of socialist, syndicalist, and anarchist militants.
The record-breaking demonstration took place in May 24, 1936: 600,000 people, led by Léon Blum and Maurice Thorez, right in the middle of the strikers movement, several weeks after the start of the Popular Front.
"Tombe sans croix et sans chapelle, sans lys d'or, sans vitraux d'azur, quand le peuple en parle, il l'appelle le Mur." - Joules Jouy
"Tomb without a cross or chapel, or golden lilies, or sky blue church windows, when the people talk about it, they call it The Wall." - Joules Jouy
Issue #161 -
Serra do Mar
Serra do Mar (Portuguese for Mountain Range of the Sea) is a 1,500 km long system of mountain ranges and escarpments in Southeastern Brazil, which runs in parallel to the Atlantic Ocean coast, from the state of EspÃrito Santo to Santa Catarina.
The main escarpment forms the boundary between the sea-level littoral and the inland plateau (planalto), which has a mean altitude of 400 to 500 m. The mountain ranges are discontinuous in several places and receive individual names, such as Serra da Mantiqueira, Serra de Bocaina, Serra de Paranapiacaba, Serra Negra, Serra dos Órgãos, etc. It also extends to some large islands near the coastline, such as Ilha Bela and Ilha Grande. The highest point of Serra do Mar is the Pico das Agulhas Negras, located in the Parque Nacional de Itatiaia in the states of Rio de Janeiro and São Paulo, with a height of 2,878 m.
Serra do Mar, in the state of Paraná, Brazil
Geologically, the Serra do Mar belongs to the massive crystalline rock platform that forms Eastern South America and tectonically is very stable. Most of the elevations of Serra do Mar were formed about 60 million years ago.
At the time of discovery of Brazil (1500), Serra do Mar supported a rich and highly diversified ecosystem, composed mainly by a lush tropical rain forest, called Mata Atlântica (Atlantic Jungle). Due to to urbanization and deforestation, however, most of the forest cover was destroyed and it remains almost exclusively in the steep escarpments facing the sea. A chain of national and state parks, ecological stations and biological reservations now protect the Mata Atlântica and its biological heritage, but acid rain, pollution, poachers, clandestine loggers, forest fires and encroachment by urban areas and farms are still promoting active destruction, particularly around cities. The largest metropolis of Curitiba, São Paulo, Rio de Janeiro and Vitória are near the Serra do Mar.
Reforestation and recuperation of biological diversity are notorious difficult to occur in destroyed rain forest habitats, but Rio de Janeiro city boasts of such success in the Mata Atlântica in its city parks.
Issue #162 -
Sacramento River Delta
The Sacramento River Delta is an expansive inland river delta in northern California in the United States. It is formed at the western edge of the Central Valley by the Sacramento River at its confluence with the San Joaquin River just east of where the river enters Suisun Bay (an upper arm of San Francisco Bay). The city of Stockton is located on the San Joaquin River near the southeast edge of the delta.
Sacramento River Delta. The Sacramento River flows into the delta from the north, meeting the San Joaquin River as it flows from the south. The main channel of the Sacramento continues westward into Suisun Bay, which empties into San Pablo Bay via the Carquinez Strait.
The delta consists of a myriad of small natural and man-made channels (locally called sloughs), creating a system of isolated lowland islands and wetlands (defined by dikes or levees). The extensive system of earthen levees has allowed wide-spread farming throughout the delta, one of the most fertile agricultural areas in California. However, a burst dike can result in the flooding of a vast tract of land. On June 4, 2004, a 350 foot (110 m) section of a levee 10 mi (16 km) west of Stockton collapsed, flooding the Upper Jones Tract, a 648 acre (2.6 km²) "island".
The many channels throughout the delta are a popular destination for boating and fishing, and provide habitat for migratory birds. Before the building of more modern highways, automobile transportation throughout the area was accomplished by roadways along the levees and one of the most extensive systems of cable ferries in North America. Today, channels of the delta are spanned by over 50 drawbridges.
The Sacramento River Delta is given as an example of an inverted river delta. The fan-shaped area of the of the delta converges downstream, rather than diverging, as the two rivers are forced to exit the Central Valley through the Coast Range via the narrow channel known as the Carquinez Strait leading into the San Francisco Bay.
Issue #163 -
Parkfield earthquake
The Parkfield earthquake is a name given to any large earthquake that occurs in the vicinity of the town of Parkfield, California. The San Andreas Fault runs through this town and has consistently produced a magnitude 6.0 or greater earthquake roughly every 22 years since 1857.
Earthquakes may occur regularly here because the location is about midway on a fault segment between a locked segment to the south (last major earthquake 1883) and a creeping segment to the north where two tectonic plates are continuously moving without major earthquakes.
The most recent significant earthquake to occur here happened on September 28, 2004.
Activity snapshot 35 hours after a Parkfield earthquake on Sept 28, 2004.
Analysis
The 6.0 magnitude primary shock was the result of a fault movement of about 18 inches (.5 meter). There have been no indications found that could have been used to predict this earthquake. Although well overdue, the probability of this quake occurring in 2004 has been estimated at about ten percent. The magnitude of the event was consistent with previous earthquakes in this region.
Aftershocks
Substantial aftershocks continued for more than a week after the initial event, moving in a northwesterly progression. In early October, there was a cluster of small earthquakes near Paso Robles near a parallel fault to the west. These may be in response to the transfer of stress to these faults after the release of stress at Parkfield. Past earthquakes have also occurred to the east of Parkfield at about the same distance from the San Andreas Fault near Coalinga and Avenal.
Aftershocks on October 11, 2004.
Recent developments
In December 2004, seismologists at the University of California, Berkeley announced the discovery of subtle tremors near Cholame, a hamlet near the San Andreas Fault directly south of Coalinga. This is in a region of the locked fault below the Parkfield episodes, last creating a 7.8 magnitude quake at Fort Tejon in 1857. These tremors were discovered using deep borehole seismometers that avoid surface noise. The spectral signatures of these motions are more similar to those of magma movement near volcanos than of typical earthquakes, but it is believed that the motions are not due to magma or fluid motion. It is hoped that this new discovery may sometime inform scientists as to the degree of danger presented by known locked faults. It is not currently expected that this knowledge will be refined into a precise predictive tool.
Fort Tejon earthquake
What is possibly the largest earthquake on the San Andreas fault in the last several hundred years is the 1857 Fort Tejon earthquake, with a fault rupture from the general vicinity of Parkfield to San Bernardino in Southern California, a distance of about 360 km (225 miles) and an offset of about 9 meters (30 feet). The epicenter of this earthquake is (by various sources) believed to be somewhere in the region from Cholame to Parkfield, a location at the extreme northern end of the locked portion of the fault and at the southern end of the rapidly periodic segment. It is believed that this earthquake was preceded by a magnitude 6.0 foreshock that was centered at Parkfield.
Issue #164
