Land Bridge

IN GEOMETRICAL TERMS, a square also qualifies as a rectangle—a four-sided plane figure with four right angles—but a rectangle does not always meet the criteria to be a square—a figure having four equal sides. Such is the case with land bridges and isthmuses. An isthmus qualifies as a land bridge—a strip of land linking two landmasses, allowing free migration in both directions—but a land bridge is not always an isthmus, which is a narrow land bridge; the Isthmus of Panama, measuring 30 mi (48 km) at its narrowest point, for example, is an isthmian land bridge, whereas the Bering land bridge is believed to have been approximately 1,000 mi (1,609 km) wide during the Pleistocene Ice Age and would not have been considered an isthmus.

Land bridges are temporary in nature, and can disappear and reappear when geologic changes occur to the land or when the sea levels rise and submerge them or lower to expose these bridges of land. In addition to the above-mentioned Bering land bridge between Siberian Asia and ALASKA, the SINAI PENINSULA (23,500 square mi or 61,000 square km) is a triangular land bridge, linking northeast Africa with southwest Asia, and is home to over 200,000 people (1986). The Torres Strait waters (90 mi or 145 km wide) between PAPUA NEW GUINEA and AUSTRALIA have contained various land bridges when the sea levels were lower, exposing the continental shelf.

The migration of people and species across land bridges during glacial periods is what interests many scientists. Numerous species of flora, fauna, and animals have extended their ranges to new lands because of the isthmuses and land bridges that have intermittently connected different lands. Today, it is believed that the first humans in North America entered by way of the Bering land bridge, also referred to as Beringia, and although many Native Americans dispute these claims based on spiritual beliefs, archaeologist finds in both SIBERIA and the Bering land bridge region indicate similar tools, dwellings, and practices distinct to the Siberian region, suggesting there was a human migration between the two regions. Beringia was wide grassland and it is highly likely that people made it a home—however brief because of the cold climate.

The population of the Sinai Peninsula is primarily along the coast, and the main industries include fishing, mining, and tourism. Harsh weather makes this land bridge a natural barrier between the competing interests in the surrounding countries. The ongoing disagreements have led to several conflicts, primarily over the Suez Canal along the western perimeter of the peninsula. Active land bridges serve as important trade routes, and the Sinai Peninsula controls much of the trade between Asia and Africa, illustrating the role past land bridges have played.

In the Torres Strait, several islands composed primarily of granite in the western waters are all that remains of the land bridge. These islands include Waiben, Badu, Kiriri, and Gebar, among others. It is possible to see Pleistocene volcanoes in the area, and approximately 17 islands in the Torres Strait are currently inhabited. The islands act almost like steppingstones between Australia and Papua New Guinea, with a “trail” of flora, fauna, people, and customs traceable from landmass to landmass.

Geological similarities between Africa, South

America, Australia, INDIA, and ANTARCTICA indicate that 150 to 300 million years ago, a supercontinent, referred to as Gondwana or Gondwanaland, made up of these countries could have existed. Recent studies suggest that land bridges might have connected the regions, rather than one large land mass, and new developments in the fields of geology and geography will likely help to answer these questions in the future.

Lacustrine Plain

ALSO CALLED A lake plain, a lacustrine plain is an area created out of deposition largely related to the past existence of lakes in the area, although in some cases, the original lakes still exist, having shrunk in size over time. Lacustrine refers to the condition of being affected by a lake or several lakes. Lacustrine plains are some of the flattest of all landform features and have few surface interruptions, although they may contain freshwater marshes, aquatic beds and lakeshore environments. 

Lacustrine plains are of varying origin, but most are underlain by fine, flat-bedded silt and clay deposited in lakes. The plains are typically related to the impoundment of water by one of the following processes: GLACIATION, differential uplift, and lake creation in now-arid inland basins.

Lacustrine plains that are glacial in origin are known as glaciolacustrine plains, and these are largely created from the trapping and ponding of water on the irregular land surface left by the former continental glaciers. In regions where there were thick masses of stagnating continental ice, steep-sided holes through the dead ice occasionally held lakes. Water was retained in these lakes by the ice walls. Fine-grained sediments (muds) accumulated on the lake bottoms. Once the ice walls melted away, however, the lakes drained, leaving the lake bottoms as plateau-like features underlain by fine-grained sediments. These lakes are largely ephemeral or temporal, eventually draining after the ice is gone. The present Great Lakes region in North America is bordered in many places by extensive lacustrine plains showing the former extent of the lakes. The Lake Agassiz plain is the biggest of these, reflecting the size of the former lake which was bigger than all the present Great Lakes put together.

The lack of topography of glaciolacustrine plains is due to the infilling of deep parts of the lake with clays and silt and wave erosion on the shallower parts of the lake. In North America and some other parts of the world, glaciolacustrine plains are of greatest interest because they often provide suitable land for intensive agriculture, and their flat topography permits mechanized farming. Lake ERIE and Saginaw Bay on Lake HURON were once much higher and extended inland, and the bottom of those bodies of water now makes up the lacustrine plains near Saginaw and Monroe. Large cities such as Chicago, Cleveland, Detroit, and Toledo also originated on the flat plains, where the dry beach ridges of the former lake edges served as roads. The flat lacustrine plains continue to absorb the urban expansion of these cities today. One handicap is that such areas are also poorly drained. Chicago lies on a plain formed when Lake MICHIGAN stood higher, and the city is often beset by the flooding of sewers, basements, and underpasses.

Other lake plains not associated with glaciers include the Congo Lake Plain and the lake plain of south SUDAN in Africa. These broad, flat plains of fine sediment were formed originally as enormous, in-filled basins created through differential uplift during the middle and late Pleistocene. The lakes were drained when the NILE and CONGO rivers eventually eroded their valleys, exposing large expanses of the former lake floors.

Lacustrine plains are also found in inland sites of present arid areas. The lakes associated with these plains were formed in a time of increased rainfall and reduced evaporation. The Chad Basin Plain in Africa, the Lake Eyre Plain in central AUSTRALIA, the plains around the CASPIAN SEA and the plains formed by Lake Bonneville in western UTAH are notable examples. The size of lacustrine plains varies according to the size of the original lake. The Superior Lake Plain, covering parts of the U.S. states of MICHIGAN, MINNESOTA, and WISCONSIN, is roughly 1,910 square mi (4,950 square km) in size. The Chad Basin Plain extends to about 919,554 square mi (2,381,635 square km) in size and is shared by seven countries: NIGERIA, NIGER, ALGERIA, Sudan, CENTRAL AFRICA REPUBLIC, CHAD, and CAMEROON.

Kyushu Mountains

THE KYUSHU MOUNTAINS form the high, elevated central portion of the Japanese island of Kyushu, the southernmost of JAPAN’s four main islands. Running roughly diagonally across the island, northeast to southwest, they cut Kyushu into a northern and southern sector. These sectors differ markedly from each other in many ways, from geology to economics: the north is urban and industrial, while the south is agricultural and poorer. The central part of the range has peaks over 3,300 ft (1,000 m), with the highest elevations at the northern end, overlooking the Aso ash and lava plateau. Mount Aso is the world’s largest volcano and last erupted in January 2004, highlighting the range’s status as one of the most geologically active places on the planet, with numerous volcanoes and hot springs, such as the famous resort at Beppu.

The island of Kyushu lies at the intersection of three tectonic plates. The core of the island was formed where the Seinan mountain arc (coming south from the island of Honshu) intersects with the mostly submerged arc of the Ryukyu Islands, which penetrates Kyushu from the south. The topography is broken up into narrow valleys cutting through steep slopes. The Kuma River is the chief waterway and flows northward into a gorge famous among trekkers. Restricted lowland area means that there has been a high degree of terracing for rice cultivation, though the population in general is rather sparse compared to the rest of Japan.

Orange groves and forestry dominate the local economy, though there has been recent growth in mineral processing industries (gold, copper, petroleum) on the eastern coast, where the ruggedness of the coast—with mountains descending directly into the sea in places—has created small protected natural harbors with relatively deep waters. The Ono River provides the needed water for these factories, as well as hydroelectric power.

Kyrgyzstan

LANDLOCKED AND MOUNTAINOUS, the Kyrgyz Republic achieved its independence in 1991 following the collapse of the Soviet Union. Kyrgyzstan features spectacular mountain vistas and incredible natural beauty reminiscent of SWITZERLAND. Despite its natural beauty and recent attempts to develop a thriving tourist industry, Kyrgyzstan remains mired in poverty. Additional challenges include implementing democracy, combating ethnic tensions, and thwarting terrorism. Central Asia’s second-smallest country in terms of area, Kyrgyzstan borders KAZAKHSTAN to the north, CHINA to the east, TAJIKISTAN to the south, and UZBEKISTAN to the west.

Kyrgyzstan is dominated by the TIAN SHAN (primarily) and Pamir (in the south) mountain ranges. The vast majority of the country (roughly 75 percent) is continuously covered by snow and glaciers. Traversing the Tian Shan remains relatively difficult, as a summer trip from the northern capital of Bishkek to the southern second-largest city of Osh (a distance of 186 mi or 300 km) takes more than 10 hours by automobile. 

Kyrgyzstan is also home to numerous alpine lakes, the largest and deepest of which is Lake Issyk-Kul, located near the Kazakh border in the north. The lake reaches a depth of 2,300 ft (700 m); its clear, sky-blue water and health resorts make the lake a popular tourist destination. For a country its size, Kyrgyzstan has surprising climatic variability, ranging from polar to dry continental through the mountains, to temperate northern foothills, to subtropical in the southwest. Kyrgyzstan’s most valuable natural resource may be its gold deposits. The Kyrgyz republic was home to the Soviet Union’s largest gold mine (Makmal), which continues to be one of the largest proven gold reserves in the world.

Kyrgyzstan’s population is ethnically diverse, including Kyrgyz (64.9 percent), Uzbek (13.8 percent), Russian (12.5 percent), Dungan (1.1 percent), Ukrainian (1 percent), and Uygyr (1 percent) peoples. Population distribution is concentrated in the Fergana, Talas, and Chu valleys and is centered in the cities of Bishkek (the capital, 2004 population 866,300) and Osh (2004 population 229,700). Most citizens are adherents to the religion of Islam (75 percent), although a sizable minority of Russian Orthodox (20 percent) exists. A secular state, Kyrgyzstan has two official languages, Kyrgyz and Russian.

Kyrgyzstan’s economy, like that of other poor countries, is dominated by the agricultural sector. A full 55 percent of the labor force is engaged in farming. Nomadic herders raise sheep (for both meat and wool), cattle, and yaks. Other agricultural products include cotton, tobacco, and a variety of vegetables. Industry, which accounts for just 15 percent of the labor force, is limited to gold, small machinery, textiles, and food processing. During its first decade of independence, Kyrgyzstan implemented more market-oriented economic reform but experienced slower economic growth than the other former Soviet republics of Central Asia.

Perhaps the most pressing geographical/political issue facing Kyrgyzstan is its complex western boundary with Uzbekistan and Tajikistan. Three large Tajik exclaves exist entirely within Kyrgyzstan’s borders, and a serious boundary dispute continues with Uzbekistan. Here, seemingly arbitrary boundaries fragment ethnic groups and unite dissimilar peoples. Kyrgyzstan’s relative location has also fostered a growing problem of illegal narcotics traffic. The country has become a corridor for the movement of opium and heroin produced in AFGHANISTAN and Tajikistan, bound for the European market. Combating terrorism represents an additional problem confronting Kyrgyzstan. Radical Islam has penetrated the country, and Osh is considered by many to be the Soviet Central Asian headquarters of Wahhabism.

Kyrghiz Steppes

THE KYRGHIZ STEPPES is a historic name for the region currently forming central and eastern KAZAKHSTAN. It is a broad plain with few to no trees and little moisture. It is a land of horses and cattle and wideopen plains. The name is confusing, and thus used less frequently today, since the actual Republic of KYRGYZSTAN contains no STEPPE at all, while the Republic of Kazakhstan is home to very few Kyrgyz people.

The confusion stems from the 18th- and 19th-century conquest of the region by imperial RUSSIA. Russian authorities were unclear about the differences between the Turkic peoples of the plains and those of the high mountain valleys to the south and east, and for a time, they were both known as Kyrghiz, or Kyrghiz-Kazakh and Kara- (or Black-) Kyrghiz, respectively. The languages of the two groups are nearly the same, and the Russians already used the term Kazakh, or Cossack, to refer to similar nomadic (though Slavic) people who lived in southern Russia. It was not until the 1920s, when the communists began to separate the peoples of Central Asia into ethnically defined autonomous republics, that the name Kazakh was used to distinguish the peoples of the steppes from those of the mountains.

Like the rest of the steppes that cross most of southern Russia, the steppes of northern Kazakhstan are broad flat plains that contain enough moisture to support grasses, but not enough to allow for denser vegetation and forests.

The Kyrghiz Steppes in particular forms the northern third of Kazakhstan and can be divided into two zones. The western zone is in the center of the country, known as the Turgai plateau, starting north and northeast of the ARAL SEA. This plateau is marked by a central depression, with a chain of lakes stretching up to the Russian border. This was once a strait connecting two inland seas, millions of years ago. The Turgai and Irgiz rivers flow into semisalty lakes, which sometimes disappear altogether in especially dry periods. 

The eastern region is known as the Kazakh folded steppe and is generally hillier, with scattered higher massifs, including the Ulu-Tau, Karkaral, and Chingiz-Tau mountains. Geologically, these folds are related to the folds in the Altai and TIAN SHAN ranges. Some of these areas are rich in mineral resources, and cities were developed during the Soviet era, such as Karaganda, the fourth-largest coal-producing city in the former Soviet Union. These cities always struggled to provide themselves with enough water, however, both for their growing populations and for industrial needs. Water resources from the Irtysh Valley in the northern edge of this steppe were used for these purposes, as were waters from the Ili River, which flows into Lake BALKHASH, and waters that were diverted from the Syr Darya far to the south, resulting in the serious shrinkage of the Aral Sea.

Other projects initiated during the Soviet era converted large percentages of the formerly open steppes into cultivated agricultural land, again with serious drain on local water resources and a change in the traditional nomadic lifestyle of the local population.