Estimates of rheologic properties for flows on the Martian volcano Ascraeus Mons

Abstract

Morphological measurements on six well‐defined volcanic flows near the summit of the Martian volcano Ascraeus Mons were used to calculate the yield strength and viscosity of the lavas. The yield strength estimates range from 3.3×104 to 8.3×104 Pa (N m−2), with an average value of 2.1×104. These values are similar to yield strengths calculated for other flows on Martian and terrestrial shield volcanoes, but they are an order of magnitude less than the value for terrestrial andesite flows and two orders of magnitude greater than values for lunar flood basalts. Lengths of the Ascraeus Mons flows indicate lower limits on the effusion rate of 18–60 m3 s−1, with an average value of 35. Effusion rate and yield strength are used to calculate upper limits on the lava viscosity of 6.4×105 to 2.1×108 Pa‐s, with an average value of 2.3×107 (equivalent to 2.3×108 poise). Ridges on one flow indicate a viscosity lower limit of 1.1×108 Pa‐s for a ridge growth time of one hour. The estimated rheologic properties of the Ascraeus Mons flows are most consistent with basaltic or basaltic andesite lavas, but some individual flows may consist of more highly evolved lavas.

Arecibo radar imagery of Mars: The major volcanic provinces

“…This bright feature is consistent with studies based on orbiter imagery, which reveal a dense array of fresh-appearing lava flow channels extending from the caldera rim to well down the upper flanks of the shield (Mouginis-Mark, 1981, 1982bZimbelman and Greeley, 1983;Zimbelman, 1985a;Zimbelman and McAllister, 1985;Mouginis-Mark and Christensen, 2005;Hiesinger et al, 2007). Rheological studies of the Ascreaus summit flows suggest that the lavas are likely to have a basaltic/ andesitic composition and an a'a flow texture (Zimbelman, 1985b;Zimbelman and McAllister, 1985;Hiesinger et al, 2007). Such a rough texture would be consistent with a radar-bright feature, although the extreme brightness and high circular polarization ratios suggest that the flow texture is likely to be blockier than is typical of a'a lavas (see Section 7).…”

Minimum estimates of the amount and timing of gases released into the martian atmosphere from volcanic eruptions

“…Leveed, channelized flows with lobate fronts also resemble basaltic lava flows. Models relating the morphometry of these flows to rheologic properties suggest that they are basaltic to basaltic andesite in composition (Hulme, 1976;Schaber et al, 1978;Moore et al, 1978;Zimbelman, 1985). (2) Comparison of global Thermal Emission Spectrometer (TES) data with terrestrial rock samples indicates that most of the martian surface is basaltic in composition (Bandfield et al, 2000).…”

Volcanism on the Red Planet: Mars

“…What is the topography of Martian volcanoes and lava flows? The slope and thickness of individual flows are very poorly constrained and estimates of lava rheology (e.g., Zimbelman, 1985;Cattermole, 1987;Lopes and Kilbum, 1990;Glaze and Baloga, 1998) at the time of emplacement may be significantly in error. Similarly, the summit caldera volumes and edifice heights might also be in error, which has important implications for the volume of the magma chamber, the size of a caldera-forming event (Zuber and Mouginis-Mark, 1992), and the dynamics that initiated the eruption (Wilson and Head, 1994).…”

“…The appearance of most volcanoes and lava flows is consistent with low-viscosity basaltic volcanism (Blasius and Cutts, 1981;Hodges and Moore, 1994). Attempts to derive compositionally dependent parameters by matching flow morphology to rheology suggest compositions ranging from basalt to andesite (Hulme, 1976;Malin, 1977;Moore et al, 1978;Zimbelman, 1985). Landforms suggestive of silicic volcanism are represented by a few highland structures resembling volcanic domes, a possible composite volcano (Greeley and Spudis, 1978), and festooned flows (Fink, 1980;Hodges and Moore, 1994).…”