The Baltoro Glacier, at 63 km (39 mi) in length, is one of the longest glaciers outside the polar regions. The glacier gives rise to the Shigar River, which is a tributary of the Indus River. It’s located in the Gilgit-Baltistan region of Pakistan, home to some of the world’s highest mountains. The glacier runs through part of the region’s Karakoram mountain range, near a mountain known as K2. The trough of this glacier is very wide. Small valley glaciers form ice falls where they meet the trunk glacier. The sidewalls vary from very steep to precipitous. The glacier has carved striations on the surrounding country rocks. Moving ice has formed depressions, which serve as basins for numerous glacial lakes.