GC Leong Test : The Earth's Crust - 2 - BPSC (Bihar) MCQ

• Compressional forces set up by earth movements may produce a thrust or reverse fault and shorten the crust.

• A block may be raised or lowered with surrounding areas. In general large scale, Block Mountains and rift valleys are due to tension rather than compression.

• The faults may occur in series and be further complicated by tilting and other irregularities. Denudation through the ages modifies faulted landforms.

• Volcanic mountains, These are, in fact, volcanoes which are built up from material ejected from fissures in the earth's crust.

• The materials include molten lava, volcanic bombs, cinders, ashes, dust and liquid mud.

• They fall around the vent in successive layers, building up a characteristic volcanic cone. Volcanic mountains are often called mountains of accumulation.

The correct answer is Aravalli. A mountain or landform that has been cut down by denudation becomes low and flat.

• When a tectonic plateau is enclosed by fold mountains, it is known as intermont plateau. Examples include: Tibetian Plateau between Himalayas & Kunlun. Bolvian Plateau between ranges of Andes.

Volcanic plateaux:

• Molten lava may issue from the earth's crust and spread over its surface to form successive sheets of basaltic lava.

• These solidify to form a lava plateau. Some of the better known volcanic plateaux are the Antrim Plateau of Northern Ireland and the north-western part of the Deccan Plateau

Dissected plateaux:

• Through the continual process of weathering and erosion by running water, ice and winds, high and extensive plateaux are gradually worn down, and their surfaces made irregular.

• In the humid highlands, stream action and sometimes glaciation cut deep, narrow valleys in the plateaux, which are then described as dissected plateaux.

• An example is the Scottish Highlands. In drier countries, vertical corrosion by rivers and abrasion by winds will dissect the plateau into steep-sided tabular masses termed mesas and buttes, intersected by deep canyons.

• This is a common feature of arid and semi-arid areas, e.g. in the south-western U.S.A.

• Many of the world's plateaux have rich mineral resources and have been actively mined.

• The African Plateau yields gold, diamonds, copper, manganese and chromium.

• In the Brazilian Plateau, there are huge resources of iron and manganese, particularly in the Minas Gerais area.

• The Deccan Plateau has deposits of manganese, coal and iron and the plateau of Western Australia is rich in gold and iron.

These plains are carved by the agents of erosion. Rain, rivers, ice and wind help to smooth out the irregularities of the earth's surface, and in terms of millions of years, even high mountains can be reduced to low undulating plains. Such plains of denudation are described as peneplains a word meaning ‘almost plains'. Pediments and pediplains are erosional plains.