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Ascraeus Mons Lava Flow
Figure 1. Flow margin and channel outlines of the Ascraeus Mons flow. Flow sections (proximal, medial, distal), distances from inferred source area, and previous topography (dome, crater) are labeled. Outline is of a mosaic of non map-projected THEMIS daytime infrared images. (b) Locations of THEMIS and MOC visible images listed by figure number.1
Longer than any known lava flow on Earth, the channeled lava flow of Ascraeus Mons Volcano, Mars is 690 km (429 miles) long1. Though enormous compared to terrestrial counterparts, the Ascraeus Mons flow has similar morphological features to the 1907 flow on Mauna Loa Volcano and the Mana flows of Mauna Kea Volcano, Hawaii1. Combining field work data from the Hawaiian field sites, orbital images of Ascraeus Mons, and experimental modeling, we were able to measure the width, length, and volume at different points along the Ascraeus Mons flow, calculate effusion rates, estimate the flow's duration, and interpret the formation processes for the flow's morphologic features.
The Ascraeus Mons lava flow is situated in the saddle region between Pavonis Mons and Ascraeus Mons1. The source volcano, Ascraeus Mons, is one of the four large Tharsis shield volcanoes and measures 375 km by 870 km at the base and is 15 km high1. The lava flow has flow thickness =110 m and a =,35 m deep channel. We calculated effusion rates of 19,000-29,00m m3/s and eruption durations over 3 to 7 Earth months, assuming a constant eruption and effusion rate1. In comparison, the 1907 Mauna flow lasted 15 days, reach a total length of ~222 km along the eastern limb, had a channel depth of 2 to 7 m, and an average effusion rate of ~119 m3/s 2. See more information about the 1907 Mauna Loa flow.
The two flows are quantitatively different as demonstrated by the at least one order of magnitude difference in flow dimensions and eruption parameters. When comparing the morphologic features, however, qualitative similarities are apparent. Both flows have three distinct regions: the proximal, medial, and distal zones. The proximal section has an indistinct or very thin flow margin present, the medial section has well-defined levees and a flow margin, meanwhile the distal section is a wide, thick non-channeled lobe1. The flow width increased downstream at the boundary of the medial and distal zones for the Ascraeus Mons flow, 1907 flow, and the experimental wax flows1. Also, the island structured observed within the channel of the medial section of the Ascraeus Mons flow resemble island feature sin the Mauna Loa flow and most likely formed during surges of lava in the channel as observed during the 1984 eruption on Mauna Lao.
Another aspect of the research included determining why a portion of the martian lava channel within the medial section cuts off and then appears again further downstream, creating a section along the "channeled" portion of the flow where no channel is present (Figure 1a). Three potential mechanisms have been suggested based on observations of terrestrial lava channels: 1) roofing of the channel, 2) the stalled and solidified remnant lava in the channel, or 3) lava backed up behind a dam that formed within the channel1.
Overall, understanding the morphology of the Ascraeus Mons lava flow on Mars propels our knowledge of the emplacement processes and eruption conditions on Ascraeus Mons volcano and the other Tharsis volcanoes, allowing us to envision what it was like on the surface as these volcanoes formed.
1. Garry et al. (2007), Morphology and emplacement of a long channeled lava flow near Ascraeus Mons Volcano, Mars.
2. Zimbelman et al. (2008) 1907 paper in press.
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