Moraine
Topic: Landforms and their Evolution: Rivers, Groundwater, Glaciers, Waves and Wind · NCERT: Class 9, Ch 2 "Shaping of the Earth's Surface"; Class 11, Ch 6 "Landforms and their Evolution"
Meaning
A moraine is a ridge or sheet of glacial till, the unsorted, angular debris that glacier ice drops directly. Glaciers pick up rock by plucking and abrasion and carry it along. When the ice melts, it leaves this debris behind as moraines. The main types are:
- Terminal moraine: lies across the valley at the glacier's end.
- Lateral moraine: lies along the valley's sides.
- Medial moraine: runs down the middle where two glaciers merge.
- Ground moraine: an uneven sheet of till over the valley floor.
Moraines can dam lakes that supply water and hydropower. They also matter for hazards, because a weak moraine dam can burst.
Example
South Lhonak lake in Sikkim is held back by a moraine. In October 2023 the moraine dam gave way, and the lake burst out as a glacial lake outburst flood (GLOF), sending a flood down the Teesta valley.
Don't confuse with
- Esker: an esker is a winding ridge of sorted gravel laid by meltwater streams under the ice. A moraine is unsorted till dropped by the ice itself.
Related concepts
- Glacial till
- Outwash deposit
- Terminal moraine
- Lateral moraine
- Medial moraine
- Esker
- Outwash plain
- Drumlin