and channel-fed flows indicates lava viscosities within the range of typical basalts (between 100 and 1 million Pa s−1). Calculated flow rates are also lower than originally thought, ranging from 10 to 1.3 million m3 per second. The lower range of eruption rates for Alba Mons is within the range of the highest terrestrial volcanic flows, such as the 1984 Mauna Loa, North Queensland (McBride Province), and the Columbia River basalts. The highest range is several orders of magnitude higher than the effusive rates for any terrestrial volcano. Since the late 1980s, some researchers have suspected that Alba Mons eruptions included a significant amount of pyroclastics (and therefore explosive activity) during early phases of its development. The evidence was based on the presence of numerous valley networks on the volcano's northern flanks that appeared to be carved by running water (see below). This evidence combined with thermal inertia data, which indicated a surface dominated by fine-grained materials, suggested an easily erodible material, such as volcanic ash, was present. The volcano's extremely low profile is also more easily explained if the edifice were built largely from pyroclastic flow deposits (ignimbrites). More recent data from Mars Global Surveyor and the Mars Odyssey spacecraft have shown no specific evidence that explosive eruptions ever occurred at Alba Mons. An alternative explanation for the valley networks on the north side of the volcano is that they were produced through sapping or melting of ice-rich dust deposited during a relatively recent, Amazonian-aged glacial epoch. In summary, current geologic analysis of Alba Mons suggests that the volcano was built by lavas with rheological properties similar to basalts. If early explosive activity happened at Alba Mons, the evidence (in the form of extensive ash deposits) is largely buried by younger basaltic lavas. Tectonic Features The immense system of fractures surrounding Alba Mons is perhaps the most striking feature of the volcano. The fractures are tectonic features indicating stresses in the planet's lithosphere. They form when the stresses exceed the yield strength of rock, resulting in the deformation of surface materials. Typically, this deformation is manifested as slip on faults that are recognizable in images from orbit. Alba's tectonic features are almost entirely extensional, consisting of normal faults, graben and tension cracks. The most common extensional features on Alba Mons (and Mars in general) are simple graben. Graben are long, narrow troughs bound by two inward-facing normal faults that