enclose a downfaulted block of crust (pictured right). Alba has perhaps the clearest display of simple graben on the entire planet. Alba's graben are up to long, and have a width on the order of –, with depths of –. Tension cracks (or joints) are extensional features produced when the crust is wrenched apart with no significant slippage between the separated rock masses. In theory they should appear as deep fissures with sharp V-shaped profiles, but in practice they are often difficult to distinguish from graben because their interiors rapidly fill with talus from the surrounding walls to produce relatively flat, graben-like floors. Pit crater chains (catenae), common within many graben on Alba's flanks, may be the surface manifestation of deep tension cracks into which surface material has drained. The graben and fractures around Alba Mons (hereafter simply called faults unless otherwise indicated) occur in swarms that go by different names depending on their location with respect to Alba's center. South of the volcano is a broad region of intensely fractured terrain called Ceraunius Fossae, which consists of roughly parallel arrays of narrow, north-south oriented faults. These faults diverge around the flanks of the volcano, forming an incomplete ring about in diameter. The set of faults on Alba's western flank is called Alba Fossae and the one on the eastern flank Tantalus Fossae. North of the volcano, the faults splay outward in a northeasterly directions for distances of many hundreds of kilometers. The pattern of faults curving around Alba's flanks has been likened in appearance to the grain of a piece of wood running past a knot. The entire Ceraunius-Alba-Tantalus fault system is at least long and – wide Several causes for the faults have been suggested, including regional stresses created by the Tharsis bulge, volcanic dikes, and crustal loading by Alba Mons itself. The faults of Ceraunius and Tantalus Fossae are roughly radial to the center of Tharsis and are likely a crustal response to the sagging weight of the Tharsis bulge. The faults ringing Alba's summit region may be due to a combination of loading from the Alba edifice and magma uplift or underplating from the underlying mantle. Some of the fractures are likely the surface expression of gigantic dike swarms radial to Tharsis. An image from High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) shows a line of rimless pit craters in Cyane