Recent Research - Mars Related Projects
Mars Topic 1: Paleotopography analysis of lava flows around Olympus Mons, Mars
Mars possesses a number of immense shield volcanoes: tall and broad structures comprising myriad long lava flows. Imaging and topography data show us their majestic current shapes and states, but we would also like to have some sense of how they grew and changed over time. Learning something about the supply rates of lava (called "magma" when it is still beneath the surface) to the volcano would help in this regard.
One way to figure out volcano growth rates is to look at places where lava flows are apparently not oriented in the current downhill direction. This sort of approach is known as "paleotopgraphy", with "paleo" indicating "old". Since lava reliably flows downhill, seeing flows that are not oriented downhill tells us that the topography changed between the time the flows were emplaced (possibly hundreds of millions of years ago) and now. Figure 1 shows some lava flows (traced by blue lines) south of Olympus Mons that are not proceeding in the expected direction (at a 90 degree angle to the white dashed topographic contours).
Figure 1: Plot comparing lava flow directions and downhill direction.
A likely way to change topography under a growing volcano is lithospheric flexure, or downward deflection of the strong outer layer of a planet. If Olympus Mons added material to its edifice, the weight would bend the lithosphere downward in a characteristic pattern that depends on the distribution of the lava and the thickness of the lithosphere. By running hundreds of models of this flexure, we can subtract out this loading effect to see what the downhill direction was before loading. For one such model (Figure 2) we see that our corrected downhill directions (green arrows) match the current orientations of the lava flows (black lines) quite well. In this way, we can estimate the lava flow volumes, that we can combine with estimates of the ages of the lava flows in Figure 1 to create estimates of lava flow rates.
Figure 2: Paleotopographic model of Olympus Mons edifice loading: after and before.
Reference: This work was published in JGR-Planets in 2015: Chadwick, J., P. McGovern, M. Simpson, and A. Reeves (2015), Late Amazonian subsidence and magmatism of Olympus Mons, Mars, J. Geophys. Res., 120, doi:10.1002/2015JE004875.
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