The weight of the ice on top of Lake Vostok is believed to add to the high concentration of oxygen. Oxygen from the ice gets dissolved into the water of the lake. Deposits of oxygen and other gases are trapped in the lake as well. The structure that traps them is called a clathrate. Gases trapped in clathrates are enclosed in ice and look like packed snow. These structures form at the high-pressure depths of Lake Vostok; they would become unstable if brought to the surface.