QUIZ – 2020: INSIGHTS STATIC , 10 December 2020 – Geography

Solution: c)

Shield Volcanoes:

Barring the basalt flows, the shield volcanoes are the largest of all the volcanoes on the earth. The Hawaiian volcanoes are the most famous examples. These volcanoes are mostly made up of basalt, a type of lava that is very fluid when erupted. For this reason, these volcanoes are not steep. They become explosive if somehow water gets into the vent; otherwise, they are characterised by low-explosivity.

Solution: a)

When the Lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all-round the earth. These vibrations are called earthquakes. The place in the crust where the movement starts is called the focus. The place on the surface above the focus is called the epicentre. Vibrations travel outwards from the epicentre as waves. Greatest damage is usually closest to the epicentre and the strength of the earthquake decreases away from the centre.

The velocity of earthquake waves changes as they travel through materials with different densities. The denser the material, the higher is the velocity. Their direction also changes as they reflect or refract when coming across materials with different densities.

Solution: c)

The reasons that can be attributed to the frequent landslides and debris avalanches in Himalayan region are

(i) The Himalayas are tectonically active. Thus, tectonically unstable.

(ii) They are mostly made up of sedimentary rocks and unconsolidated and semi-consolidated deposits.

(iii) The slopes are very steep.

Solution: b)

Earthquake waves are basically of two types — body waves and surface waves. Body waves are generated due to the release of energy at the focus and move in all directions travelling through the body of the earth.

There are two types of body waves. They are called P and S-waves. P-waves move faster and are the first to arrive at the surface. These are also called ‘primary waves’. The P-waves are similar to sound waves. They travel through gaseous, liquid and solid materials. S-waves arrive at the surface with some time lag. These are called secondary waves. An important fact about S-waves is that they can travel only through solid materials.

The surface waves are the last to report on seismograph. These waves are more destructive. They cause displacement of rocks, and hence, the collapse of structures occurs.

Solution: a)

Earth quakes are usually associated with volcanoes, since both are related to plate movements.

Volcanoes can also happen with ocean-ocean crust collision. Best example is South East Asian Archipelago.

Volcanoes are one of the best sources of sulphur.