Question

How was Indian desert formed

Answer 1

The southwest monsoon occurs in two branches. After breaking on the southern part of the Peninsula in early June, the branch known as the Arabian Sea monsoon reaches Bombay around June 10, and it has settled over most of South Asia by late June, bringing cooler but more humid weather. The other branch, known as the Bay of Bengal monsoon, moves northward in the Bay of Bengal and spreads over most of Assam by the first week of June. On encountering the barrier of the Great Himalayan Range, it is deflected westward along the Indo-Gangetic Plain toward New Delhi. Thereafter the two branches merge as a single current bringing rains to the remaining parts of North India in July. 
The Aravalli Hills is aligned parallel to the direction of the Monsoon and hence does not cause any significant rainfall. Both the Monsoon, (the one deflected from the Himalayas and Arabian Sea M) becomes dry once they reach Western India. The Aravalli Hills is aligned parallel to the direction of the Monsoon and hence does not cause any significant rainfall. Moreover, because it acts as a barrier to block the Monsoon, the area to the west of the Aravallis does not receive any rainfall at all. Hence Thar desert formed.