Ice has many different forms. Sea ice forms on the surface of the sea in cold regions. Once it forms it can last just a few hours or it can last for several years before it finally moves into warmer waters and melts. If it lasts several years it can be several meters thick. Snow that falls on the land in cold regions and in mountains can accumulate over many years to form glacial ice.
Some glaciers are very large.
At NASA, we are trying to understand more about these remote regions of the planet and because these regions are so remote the best way to do this is by using satellites. For instance, one thing we would like to know is whether these ice sheets are growing or shrinking. If they are changing then they could alter sea level. I hope you find this information helpful. Thank you for your interest in the NASA Earth Science Enterprise.