Thanks for your question. Many people are surprised to hear that there is a lot of water movement beneath the Antarctic ice sheet. The first thing one needs to understand is that ice is melting at the bottom in many places; where there is sufficient heat. There are two heat sources, one is the geothermal flux of heat from deep Earth interior and the other one is heat produced by friction during ice motion. The rates of melting are about a fraction of an inch per year. This is ten to hundred times less than rainfall on normal continents. However, it’s enough to feed a sluggish subglacial water system. After it’s generated, subglacial meltwater flows, just like water on surface of the Earth does. It can form streams, rivers, and lakes or flow through pore spaces and fractures in rocks and sediments. The one big difference is that water on the surface of the Earth always flows down slope. However, subglacial water sometimes flows uphill because it is pressurized by the weight of ice up above. In fact, subglacial water flow follows mostly the slope of ice surface, rather than the slope of the bedrock underneath the ice sheet. In places where the ice surface slope is gentle, like near ice divides or beneath some ice streams, subglacial meltwater gets trapped in closed bedrock basins and forms subglacial lakes. Hence, the subglacial water system in Antarctica is in many ways similar to the water systems on other continents, except that it exists beneath thousands of feet of ice.