Topography of Small Volcanoes at the Margin of the Mars North Polar Cap

Putative volcanic craterforms have been observed in the north polar region of Mars since Mariner 9. Hodges and Moore described some of these features for the region they called the 'Borealis Volcanic Field', and suggested that several were formed as a consequence of magma-ice or magmawater interactions. Mars Orbiter Laser Altimeter (MOLA) topographic measurements confirm suggest that the features are unlikely to be of impact origin, and that there are many more of them present around the north polar cap than suspected from images alone. Analysis of one of the larger features--suggested by Hodges and Moore to represent a hydromagmatic explosion crater or maar--showed topographic characteristics more similar to a terrestrial small basaltic shield volcano, possibly of recent origins. Recent work with the MOLA topography has also suggested that the possible volcanic extent of the Borealis Field is substantially larger in both number and range than previously mapped. Since the majority of these features are within 100 km of the present edge of the northern residual polar cap, and several extend into the Chasma Boreale cap re-entrant, they are some of the best Mars candidates for possible magma-water or magma-ice interactions. However, so far, these features have not displayed the expected average slope or other characteristics predicted for martian hydrovolcanic features, or even martian explosive volcanic features. Here, we show some of the range of feature types observed in the topography, along with their characteristic topographic measurements, and compare them to terrestrial and martian volcanic features. Additional information is contained in the original extended abstract.