Mars is now a dry planet with most of its water either tied up in a deep permafrost or lost to outer space. However, images gathered by Mars Observer and earlier space craft such as the Viking orbiters, showed evidence of water channels, rivers, and water erosion. The most striking evidence consists of wide enormous flood plains in the Valles Marineris area.

Dykes are created when magma from deep inside the planet swells upwards and deforms the surface. The dykes on Mars are in the Tharis bulge, a region of the Martian surface that has a large volcanic plume underneath it. These dykes are 20 times bigger than anything seen on the Earth.

McKenzie and Nimmo calculated the amount of heat required to melt the Martian permafrost and modelled their results on a computer. They discovered the dykes produced enough heat to melt at least 7500 km3 of water - enough to have radically changed the surface temperature and humidity on the planet, and produced the water erosion seen in the region.