Page 163 - General Knowledge

GENERAL KNOWLEDGE 2019

crust and builds up on the surface, whether quietly or explosively. Volcanism can form islands,
such as Hawaii, built on a series of broad basaltic shield volcanoes. Volcanoes on continents
can also appear isolated and almost island-like given their prominence, a prime example being
Washington State‘s Mount Rainier.

Plains

Most of the Earth's surface consists of low and high plains, defined by a mostly level profile that
ranges from gently rolling to completely flat. Such landforms are common in areas of extensive
sediment accumulation, as in the ―floodplains‖ and deltas of large rivers and the Atlantic-Gulf
Coastal Plain of the United States. While those examples are low-lying, higher-elevation plains
such as the Great Plains of central North America – built by sediment washed out of the Rocky
Mountains and accumulated in long-ago seaways – also exist. Keep in mind that plains describe
mostly level topography, though people sometimes incorrectly use ―plain‖ as a synonym for
grassland ecosystems (prairies and steppes). You can easily have a forested plain.

Valleys, Canyons and Caves

The erosion of rivers and the moving ice bodies called glaciers help sculpt valleys, often in
combination with faulting. Glaciers flowing down drainages tend to sculpt U-shaped valleys;
such glacially carved troughs often come to support lakes, as in the Finger Lakes of New York
State. Running water, by contrast, tends to carve out V-shaped valleys. Mountain valleys tend
to have steep walls and narrow channels – such features may be called canyons or gorges –
while valleys on plains tend to have shallow slopes and wider channels. Caves form in karsts,
where limestone, dolomite, or gypsum rocks are slowly dissolved by groundwater. Others are
formed by waves pounding cliffs on the coastlines, or where molten rock drains out the inside of
a lava tube of a volcano.
Deserts

The ecological landscapes known as deserts, defined by very arid conditions of low precipitation
and high evaporation, include plentiful mountains, plains, plateaus and canyons that include
distinctive sub-varieties of desert landforms. These include gravel plains, sand dunes and dry
lakebeds. Many natural factors are responsible for the creation of deserts, particularly current
and past climatic conditions. The Mojave Desert in California consists of 1.6 million acres of
landscapes that changed over millions of years, including mountains, canyons, volcanic fields
and dry lake basins. The region is within a great inland drainage basin where ancient lakes
overflowed into adjacent valleys and eventually spilled into Death Valley. After the region dried
up, it left dry lakebeds exposed to erosion by the wind.

IMPORTANT BOUNDARY LINES

 Durand Line is the line demarcating the boundaries of Pakistan and Afghanistan. It was
drawn up in 1896 by Sir Mortimer Durand.
 Hindenburg Line is the boundary dividing Germany and Poland. The Germans retreated
to this line in 1917 during World War I
 Mason-Dixon Line is a line of demarcation between four states in the United State.

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