Question

Hypothesis Exercise: Assignment: Id Plate Boundaries/ Features

Develop a hypothesis of the control exerted by plate tectonics on coasts. For example, how do coasts differ along passive and active margins? How does plate tectonics influence coastal variability (i.e., how coasts look)? Why are some coasts rocky and others are not?

Describe the influence of tectonics on:

1. Continental shelf width
2. Sediment supply
3. Geologic features (e.g., volcanoes, deep-sea trenches, etc.)

Answer 1

Ans.

Before answering the question, we must first understand that there can be three type of collisions on the basis of which we can make some hypotheses.

ent f_ Divergent Boundaries Transform boundaries

Lets now first understand the meaning of active and passive margins. Active margin has continuous flow of magma and is located where subduction has taken place. Such margins are quite narrow and deep like a trench (example is the Western South American coast). Such margins are tectonically active and frequently the activities like volcano, earthquakes, mountain building etc occur here. Even Indian Ocean and pacific Ocean are also the examples of Active margin. We must know that such type of margins are mostly formed by either transform or convergent boundaries.

Passive margins are formed when sedimentation takes place and represents change in the lithosphere. It is associated with divergent boundary and creates new ocean basins. They are not found near a subduction zone and are found in the region around Atlantic Ocean, Arctic Ocean, western part of the Indian ocean etc. When indian plate was moving towards Eurasian plate, it was passive margin. Since it is formed due to sedimentation, there doesnot occur mostly any volcanic activity actively. it is passive in nature.

Coastal areas differ with different activities. Some coasts have more erosion processes (cliff) while others have depositional features (Beach). Now, whether a coast is erosional or depositional, depends upon history of its formation and the tectonic activities that have occurred there. Wherever there is erosion of rocky surfaces, the sediments are softened and deposited at other places. Even the conditions differ during summers and winters. We can see higher waves in winters due to more temperature gradient and thus waves erode with more power and thus beach becomes narrow and opposite is the case during summers.

Winters wavesS steep beach due to weak waves

If there is abundant sediment supply, the relief will be gentle (near river meeting to sea). the coasts are rocks if there is continuous erosion. If the boundary is divergent, conditions will be calm i.e. passive margin whose features we have already discussed above.

I hope the answer is clear to you now, if you have any further query, leave a comment, I will try my best to solve it for you. Goodluck