As we've previously noted, mars hasn't always been as wild and desolate as it appears today. There are many indications that, not only was its atmosphere hotter and wetter, but it also sported a much larger magnetic field and much more geological activity than it does now. Amongst the best evidence for this are the vast martian lava beds and the presence of the single largest volcano in the solar system, Olympus Mons (depicted right). Olympus Mons is remarkable, not only because its height, but as it also provides a deep insight into the inner working of the planet. On Earth, large volcanoes of Olympus Mons' size are unable to form due to the movement of tectonic plates, shifting the peak of the mountain away from the lava upwelling that causes the volcano to build in height. Mars' lack of tectonic activity has allowed Olympus Mons to build in height in exactly the same place over billions of years creating the gigantic mountain we know today.
However, we're not quite certain how active mars is at the moment. New images constantly reveal new information about the surface and some of the newest images received (shown left) suggest that lava has flown across the martian surface as little as 20 million years ago (the blink of an eye on stellar timescales). The skin-like patterns are caused by the cooling and settling of the lava flows in the chill martian atmosphere, and the spirals that are visible are similar to those seen near some of the Hawaiian volcanoes on Earth. The martian spirals are far larger that Earth ones, the biggest an estimated 30 meters across, possibly due to the lower gravity on mars. Lava flows cover much of mars' surface, in fact all the darker splotches (seen in the top image on this page), which for a long time were thought to be forests, are lava beds the size of Australia!