Glaciers are normally described as a mass of ice slowly moving down a gradient. A glacier consists of ice crystals, water and rock debris. Out of this, ice is an essential part of a glacier. Based upon morphological characteristics of glaciers they can be grouped into classes such as ice sheet, ice cap, and glacier constrained by topography. Ice sheet and ice cap are formed when underlying topography is fully submerged by ice and glacier flow is not influenced by topography. On the other hand, when glaciers are constrained by surrounding topography and the shape of valley influences their flow, then such glacier are classified as valley glaciers, cirque glaciers and ice fields. Himalayan glaciers are constrained by topography and are predominantly of valley type.

 

 

  

 

 

There are 84 glacier present in the Tista basin. This covers an area of 440.300 sq.km. The total Areal extent of permanent snowfields has been measured as 251.224 sq.km. This makes total area under glaciers and permanent snowfields as 691.525 sq.km. in the Tista basin . The permanent snow cover and glaciers are distributed in 12 subbasins. the total glacier and permanent snow cover-stored water in the Tista basin is estimated as 145.05 cu km. Most of the glaciers of Tista basin have an area less than 5 sq.km. There are only two glaciers having an area more than 20 sq.km. and most of the permanent snowfields have an area of less than 1 sq.km.