Most small glaciers in the world are not as exciting as surge and tidewater glaciers. They may form on the tops of mountains and slowly make their way over hundreds of years through valleys and across plains. A change in the yearly temperature around a glacier can cause it to expand or contract.
Some glaciers tend to extend in many different directions.
As they melt, one part may retract and another part may stay put. If scientists were to travel to the glacier and measure just this section, they could be deceived. Measurements have to be made regularly at every extension of the ice cap to see if the glacier as a whole is melting, Hall said. While this may be feasible for one glacier, it is nearly impossible to measure a hundred glaciers this way. Satellite sensors such as those on Landsat 5 and Landsat 7 allow scientists to measure the entire rim of any glacier on an annual basis, cloud cover permitting.