Permafrost measurements on thermokarst shore in Alaska. Researcher measuring the depth to permafrost along a thermokarst lake shore. Thermokarst lakes form from meltwater as the permafrost slowly thaws. The presence of the water keeps the underlying ground warmer, and the lakes gradually deepen over time. These features are being studied for how they are affected by climate change and how they can contribute to global warming by directly and indirectly releasing gases such as methane and carbon dioxide. Photographed in Alaska, USA, on 11 August 2015.