Soil erosion is a continuing threat in the buffer zone between the ecozone and GHNP. It begins with sheet erosion ‒ the washing away by rain of topsoil and its nutrients from arable land. As water concentrates into mini-rivulets in the fields, rill erosion takes place. Such erosion is also common on barren slopes where all vegetation has been destroyed.
When rills can no longer be obliterated by normal agricultural operations, they are called gullies. In turn, these are widened by the monsoon rains to become nalas, which carry soil, stones and boulders downhill, thus damaging the slopes. This also silts up stream beds, reducing their capacity to carry runoff water and sediments, and consequently causing fast-flowing waters to cut into and erode banks.
GHNP is also affected by glacial erosion. Around 16% of the park’s conservation area is snowbound, and its mountain slopes are the source of avalanches which form glaciers down below. Glacial ice is abrasive and carries rock downhill to form moraines, which can block the courses of streams, thus forming lakes ‒ as in the upper reaches of Parvati Valley.