The expanse of the lava is so great that the plains show subdued swells dozens of km long from compression and brickling. The volcanoes found on Mars are almost all shield volcanoes. These are created by convection currents beneath the surface of the planet, hot, buoyant mantle rises to the surface as hot spots. This occurs on the Earth as well, in areas such as Hawaii and Bermuda. Martian volcanoes do resemble Hawaiian shield volcanoes in many ways, their eruptions are effusive and therefore quiet, they are basaltic in nature showing that the magma has reached the surface quickly and has not had long enough to partially crystallise to any extent.
Shield volcanoes have calderas and typically long lava flow channels.
In fact the main difference between shield volcanoes on Earth and those on Mars is size, Martian volcanoes are 10 - 100 times larger. Hot spots do not just form volcanoes, if they occur under a thick continental plate, as they most commonly do, the forces are sometimes sufficient to tear the crust apart forming rifts or graben. These faults occur when crust moves in opposite direction, leaving the land in the middle to drop down. On Earth this can be seen in the East Africa Rift, on Mars there is Valles Marineris . On Mars, rifting has occurred, creating an immense valley like a scar on the Martian landscape, out of proportion to anything on Earth.