How can a glacier erode below sea level but streams and rivers cannot?

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ncchemist eNotes educator| Certified Educator

A glacier is a giant mass of ice that has accumulated for many years and moves slowly from higher elevations to lower elevations and sometimes sea level.  Due to its immense bulk, a glacier will take a very long amount of time to melt even when it reaches the ocean.  As a result, it will continue to erode the ocean floor as it moves into the ocean.  Fjords are a perfect example of erosion at and below sea level as a glacier moves into the ocean.  Rivers and streams, on the other hand, are already liquid water.  When the moving water from them reaches the ocean, it quickly disperses into a large, open body of water.  As a result, the force of the flowing water very quickly disappears once it hits the ocean.  That is why rivers and streams don't erode below sea level but glaciers do.