The glacier dog sledding tours operate on the upper part of the glacier where the surface is packed snow. All other glacier walk tours take place lower on the glacier where you'll encounter different features in the ice. The surface is wet, a little bit dirty, and uneven with crevasses and seracs (towers/fins of ice). It is wet due to melting ice and from the meandering melt-water streams. It is dirty due to the movement of the glacier scraping the sides of the mountains, winds blowing dust and debris onto the ice, and 150 years worth of atmospheric dust settling onto the glacier. To prevent us from sliding while walking on the ice, we wear micro-spikes.