High-Resolution Topographic Analyses of Mounds in Southern Acidalia Planitia, Mars: Implications for Possible Mud Volcanism in Submarine and Subaerial Environments

Ryodo Hemmi,Hideaki Miyamoto

doi:10.3390/geosciences8050152

Abstract

A northern ocean of Mars is still debated and, if it existed, it may have accompanied valley networks and/or outflow channels, which may have led to the emplacement of a large amount of water to the northern lowlands during the Noachian and/or Hesperian times. However, it is unclear how and under what conditions (submarine or subaerial) geologic features such as mounds and giant polygons formed in the northern lowlands. The densely-distributed mounds in Chryse and Acidalia Planitia, >1000 km-wide basins of the northern plains, were suggested to be ancient mud volcanoes formed in an aqueous setting, which is controversial (i.e., mud vs. igneous and submarine vs. subaerial). However, these mounds have not been quantitatively well characterized, particularly with respect to their detailed topography. Here we generated forty digital elevation models (DEMs) with resolution of up to 1 m/pixel from High Resolution Imaging Science Experiment (HiRISE) stereo image pairs, and we accurately measured the morphometric parameters of ~1300 mounds within the southern part of the Acidalia basin. Their heights and diameters resulted in good accordance with those of mud and igneous volcanoes in submarine/subaerial settings on Earth. Maximum depths of their source reservoirs vary from ~30 to ~450 m for a subaqueous setting and from ~110 to ~860 m for a subaerial setting, both of which are consistent with fluid expulsion from the ~100–4500 m-thick flood deposits (Vastitas Borealis Formation, VBF). On the basis of the morphometric values, we estimated rheological properties of materials forming the mounds and found them consistent with a mud flow origin, which does not rule out an igneous origin. The conditions of possible submarine mud or igneous volcanoes may have harbored less hazardous environments for past life on Mars than those on an ocean-free surface.

Highlights

While liquid surface water is physically not stable under the current Martian climate, the former presence of a northern ocean has been proposed for the northern lowlands since either the Noachian [1,2] or the Hesperian [2,3,4]
Previous studies, such as the photoclinometric analysis of over 400 pitted mounds within Cydonia Mensae, part of the Acidalia basin, and Chryse Planitia [23,45] and mound heights derived from three Mars Orbiter Laser Altimeter (MOLA) track data in Acidalia [25], are fairly comparable to our results
The exception being that a 3D photogrammetric analysis of High Resolution Imaging Science Experiment (HiRISE) stereo pairs involving two pitted mounds by Oehler and Allen [21] resulted in heights of up to 180 m, which are an order of magnitude larger than those of our results (30.8 and 31.6 m in height)

Summary

Introduction

While liquid surface water is physically not stable under the current Martian climate, the former presence of a northern ocean (or northern oceans) has been proposed for the northern lowlands since either the Noachian [1,2] or the Hesperian [2,3,4]. There are two major views: (1) the valley networks, formed by the long-term hydrological cycle of a warm, wet climate during the Noachian, may have been associated with a persistent ocean [1]; (2) the Hesperian-aged cataclysmic floods, suggested by outflow channels debouching into the northern lowlands [5], may have left behind large amounts of water and sediments forming the northern ocean [6]. Geosciences 2018, 8, 152 marine sediments comes from the Vastitas Borealis Formation (VBF)—a roughly uniform sedimentary. Hesperian-aged indicates that the minimum average thickness with an extent approximatelyridged equal toplains the northern lowlands [7,8,9].

Results

Discussion

Conclusion