Geology of Nepal

The geology of Nepal is shaped by the Himalaya, the world’s highest and youngest mountain range. The Himalayas are very active and help scientists understand how continents crash into each other. This mountain chain stretches about 2,400 kilometers from Nanga Parbat by the Indus River in northern Pakistan to Namche Barwa by the gorge of the Tsangpo-Brahmaputra in eastern Tibet. About 800 kilometers of this great range lies in Nepal, with the rest in Bhutan and parts of Pakistan, India, and China.

About 55 million years ago, the Indian subcontinent crashed into Eurasia, starting a process called the Himalayan orogeny. This crash made the Indian crust much thicker, reaching about 70 kilometers today. Before this big crash, the northern edge of India had thin land with layers of old sand and other sediments on it.

Morpho-tectonic division of Nepal Himalaya

The rocks of the Himalaya in Nepal can be divided into five main zones from south to north. These are the Gangetic plain (Terai), the Sub Himalayan (Chure or Siwalik), the Lesser Himalayan (Mahabharat Mountain Range), the Greater Himalayan, and the Tibetan Himalayan zones.

The Gangetic plain, also called the Terai, is a fertile land in southern Nepal. It is made of soft soil and sand brought down from the northern mountains. This area is part of a larger plain that stretches into India and Bangladesh.

The Sub Himalayan zone, also known as the Siwaliks, is a belt of rocks and soil along the southern edge of the Himalayas. It contains layers of sand, mud, and rocks from rivers.

The Lesser Himalaya lies between the Sub Himalayas and the Higher Himalayas. It is made of many types of rocks, including shale, sandstone, and limestone. The rocks here have been folded and pushed by the moving mountains.

The Higher Himalaya zone contains thick layers of strong, crystalline rocks. These rocks have been changed by heat and pressure over time.

The Tibetan-Tethys zone is the northernmost part of the Himalaya in Nepal. It contains layers of shale, sandstone, and limestone that have not been changed much by heat and pressure.