Glacier runoff is the water that flows downhill from the melting of a glacier. This runoff flows into rivers, lakes, and oceans, changing their shape, depth, span, flow rates, chemistry, environment, and more. 

Runoff matters for many reasons. For example, many animal and human communities depend on runoff to reliably fill rivers, lakes, and reservoirs for drinking water. If there’s too much runoff water coming from a glacier, it can cause downstream flooding. Even more severe flooding can result from a glacial lake outburst flood (GLOF), when a natural dam bursts and releases glacial runoff. GLOF flooding can be catastrophic for communities downstream. 

The time of year when a glacier is melting and producing runoff is important, too. Because of climate change, many glaciers are melting earlier in the spring, swelling rivers sooner than usual, which can alter seasonal habitat, animal behavior, and spawning patterns. It can also lead to earlier or more severe spring floods.

Researchers and planners can use NASA’s data to measure the volume and timing of glacier runoff to determine what it means for the form and function of Earth’s landscapes and waterways.