A glacier is a big chunk of ice that is persistent, so it sticks around for a long period of time, rather than

forming and then melting back into water within just a few years or less.

It moves under its own weight, so it's not holding still, it's hanging out getting big,

and then eventually slowly shifting geographically because of how heavy all that ice it has accumulated

has become.

Glaciers are also distinct from sea and lake ice, which are sort of like glacier ice,

but based on water rather than on land.

Ice that forms on water tends to have more size and shape and weight variability because of the

nature of the water upon which it floats, and because it's more likely to move around a bit

because it's floating rather than holding still on relatively more stable land.

99% of glacial ice on Earth is located in what are sometimes called continental glaciers,

and sometimes referred to as ice sheets. These ice sheets are primarily based at the planet's poles,

because of how the globe is tilted, and thus where heat tends to aggregate. On average, more toward the equator, with less

sunlight delivered heat and fewer climactic systems moving and storing heat within the

Arctic and Antarctic regions.

But glaciers are also found elsewhere, especially in higher latitudes, because again, these are regions that tend to be

colder, and when it's consistently cold, these bodies of ice have the chance to form and then stick

around long enough to accumulate more and more ice, eventually becoming so big that their heft

causes them to start moving. Glacial ice holds

somewhere in the neighborhood of 69% of the planet's fresh water, and that's important

for many reasons, but most immediately, because runoff from these glaciers, water from portions

of them that melts and then reforms year after year, serve as a

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