How were the himalayas formed?
due to a sudden shift along a transform boundary
due to an increase in volcanic activity
when two plates collided with each other
when a mid-ocean ridge split apart

when two plates collided with each other

Explanation:

The Himalayas are the largest and highest mountain range in the whole world. They have formed as a result of a convergent plate boundary, thus collision of two tectonic plates. The plates that collided and caused their formation were the Indian plate and the Eurasian plate.

As the Indian plate separated from Gondwanaland, it started to move in north-eastern direction. As it was moving, it closed down the Tethys Ocean, and eventually hit the Eurasian continent. Because the two plates are continental, instead of one of them being subducted, they started to press each other. The enormous pressure resulted in lifting up the land around the boundary, and gradually a vast mountain range emerged. This process is still going on today, and this mountain range is still expanding and growing in height.