I only have 1 point.. They're melting. As the ends break off and melt, the glacier gets shorter.
Glaciers melt because of climate warming.
And because of the "Albedo effect" That is: If there is ice, there is white surface. The white surface reflects sunlight --> place cold. If there is no ice, sunlight shines on darker surfaces, such as Rock --> place warms up --> more ice melts --> more dark surface --> place warm up more --> and so on.
The global warming.