Have you ever seen dark cavities on glaciers, which are also referred to as “cryoconites”? These holes, which can be meters deep,are created from debris on top of glaciers. Dark-colored debris, including soot, dust, and pollen, speed up the melting process of glacial ice as a consequence of their low reflectivity to incoming sunlight. In some cases, glacial surface debris can also form pits in the ice through chemical melting. Hence, most of the glacial thaw holes are filled with melt-water, which become home to cyanobacteria, fungi, and other microbes. However, some large solid debris, in particular boulders, will prevent the ice beneath from melting as surrounding ice, forming glacier tables. Here are some photographs of cryoconites and glacier tables.
Learn more about glacial surface debris here.