A field of anomalous craterforms (termed Martion Cratered Cones MCCs) has been mapped in the Chasma Boreale region of Mars, and several authors [e.g., Hodges and Moore, 1994; Garvin et al., 2000] have suggested, based on images and topographic data, that these features are volcanic shields. This field lies directly in the path of the outflow of meltwater that may have formed Chasma Boreale [e.g. Clifford, 1993; Fishbaugh and Head, 2000].
The purpose of this paper will be to estimate the amount of melting of polar materials that could result from eruption of these shields and thus to assess whether these volcanoes of this size could produce a reentrant as large as Chasma Boreale (assuming that a similar field also lies beneath the cap in the Chasma Boreale region). Features similar to Chasma Boreale (but much smaller) have been formed on Earth due to subglacial eruption (e.g. of Grimsvotn in Iceland). Of course, if these features are volcanic shields, then the timing of their formation relative to that of Chasma Boreale is of crucial importance. If these volcanic features were formed after the Chasma Boreale outflow event, then they should have been modified by the outflow. I will characterize the morphology of several of these features and compare these observations with the expected morphology of shield volcanoes in that region [e.g. Wilson and Head, 1994] in order to understand whether the shields have been modified and by how much. There is also the possibility that these craterforms are not shield volcanoes at all but are instead impact craters that have been heavily eroded by outflow from the chasma. If I have time, I will compare the morphology of north polar region impact craters characterized by Garvin et al. [1998, 1999, 2000] to these features to assess whether the amount of fluvial erosion (volume percentage-wise) is the same as that estimated for erosion of shield volcanoes.