Standing on a glacier, seeing the foot of a glacier oozing down the slope of a mountain or even seeing a photo of a glacier online there are a lot of cool things to notice that can tell you about that glacier.
This is a photo from the Matanuska Glacier in the Chugach Mountains of Alaska. What you are looking at is a small crevasse in the glacier, which is filled with meltwater. What I think is most interesting here is the glacial debris. As a glacier flows and deforms downslope under its own weight, it crushes and entrains the material below it. I like this picture because it shows how a glacier could come to have rock debris on top of it. If you look into the wall of that crack, you get to see a vertical cross-section of the glacier in which you see other entrained debris. As the glacier thins, the debris that was sparse in the glacier, piles up on top as the ice around it turns into meltwater. This is how you may come to have a glacier topped by a pile of glacial debris. This debris absorbs more short-wave solar radiation and reflects less long-wave radiation back to space, multiplying the melting, adding more debris creating a positive-feedback.
Have you ever bent something like a stick of gum and seen cracks form on the surface of the convex side of where it was being bent. That is essentially what is going on in crevasse formation, you have brittle deformation at the surface from shear stress in the interior of the glacier. This photo is of the Portage Glacier in Alaska. Glaciers in southern Alaska flow relatively fast downslope, which means there is more shear stress, which is why you generally see a lot of crevasses in Alaskan glaciers. What one can notice looking on at glaciers like these are where all of the crevasses are being formed. All of the dark ridges are places of high crevasse formation due to three main factors: steeper slopes, faster glacial flow and where ice is being stretched over larger basal topography.
Hi my name is Nilo Bill and I am a graduate student in Geology at Oregon State University College of Earth Ocean and Atmospheric Science