Complex sentence: Crevasses often have vertical or near-vertical walls, which can then melt and create seracs, arches, etc.; these walls sometimes expose layers that represent the glacier's stratigraphy.
Split into simpler sentences: Crevasses often have vertical or near-vertical walls, which can then melt and create seracs, arches, and other ice formations. These walls sometimes expose layers that represent the glacier's stratigraphy.