Physics
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusm.p32a..06i&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #P32A-06
Physics
5480 Volcanism (8450), 8450 Planetary Volcanism (5480)
Scientific paper
Alba Patera (AP) is one of the largest shield volcanoes on Mars. Its aspect ratio is ~0.005-0.006, which is an order of magnitude smaller than the mean aspect ratio of Olympus Mons, ~0.04. We studied the region of AP using the new MOLA topographic map and Viking and MOC images in an attempt to reassess the sequence of major events at Alba with the new high resolution data. Topographically, the volcano of AP consists of two major parts, the distal apron of lava flows and the topographic anomaly of the volcano itself. Strong topographic asymmetry characterizes the AP construct. The volcano is on a regional slope (~0.2o) and has relatively steep (~1.3o) and steady northern slope ~5.2 km high. The southern slope is much shallower (~0.2o) and is ~1.5 km high. The summit area of the volcano is topped with a dome ~1.5 km tall with a summit depression. The volcano of AP has two previously unknown shoulder-like structures (lobes) at the western and eastern sides. The maximum height of the volcano is ~6.6 km. The principal sequence of events at Alba as seen in the Viking, MOC, and MOLA data appears to be as follows. The distal lava flow apron is the oldest feature of Alba. Later on, more concentrated eruptions (probably at lower rates) in the central area led to the growth of the main dome of AP. A more erodable material, the presence of which is manifested by the small valley networks, has been deposited on the slopes of the main dome of AP before the formation of the flanking lobes. Although the valley networks are abundant, they occur on slopes of the main dome only meaning that supply of the agent of erosion was rather limited. The lobes of Alba are relatively young features that may represent rift-like zones forming due to gravitational spreading of the edifice under its own weight when the rate of magma supply was still high. The recent interpretation of the new MGS data suggest that sublithospheric to intralithospheric loading may be responsible for the formation of circumferential graben at Alba. The caldera complex formation and tilting of the summit dome occurred at the very end of the evolution of AP. Effusive volcanism was predominant during almost the entire evolution of Alba. The presence of a dendritic system of valley networks has been cited as supporting the presence of plinian pyroclastic deposits from the vent within the caldera complex.
Head James W.
Ivanov Michael A.
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