• Brainly User
They are bounded on the south by a fault system called the Main Frontal Thrust, with steeper slopes on that side. Below this, the coarse alluvial Bhabar zone makes the transition to the nearly level plains. Rainfall, especially during the summer monsoon, percolates into the bhabar, then is forced to the surface by finer alluvial layers below it in a zone of springs and marshes along the northern edge of the Terai or plains.[citation needed] North of the Sivalik Hills the 1,500-3,000 meter Lesser Himalayas also known as the Mahabharat Range rise steeply along fault lines. In many places the two ranges are adjacent but in other places structural valleys 10–20 km wide separate them.
Siwalik is the southern most range of the himalayas with an average height of 1000 m.
It is a discontinuous range made up of mud and soft rocks. The narrow longitudinal valleys called Duns are found in siwalik.
Along the foothills of siwalik, pebbles and gravels are being deposited by the rivers.
Terai plain is made up of deposits of fine silts in the south of siwalik.
It supports the growth of thick forest and marshy lands.