Icy volcanic breccia
This is beautiful:
That's an image by Chris Waythomas of the USGS, hosted by the Alaska Volcano Observatory website. It shows a cutbank (river-eroded alluvium deposit) along Rust Slough, south of the Drift River Oil Terminal, northeast of Redoubt Volcano. The sediments exposed were deposited on March 22, 2009 by a lahar (volcanic mudflow). The lahar deposit is 2.5 m thick. When I saw this image tonight (as I was searching for another shot), I was particularly struck by the subrounded clasts of ice in the mud. Here is ice acting the part that chunks of rock usually play. Technically, ice is a mineral, and so these chunks are sedimentary clasts much like any other... But to me there's something distinctly different about seeing ice cobbles and pebbles included in a sedimentary deposit. On a planet as warm as Earth, this sort of thing isn't likely to be preserved in the geologic record. It would melt! ...And that gets me thinking about other planets and planet-like objects, like Titan. The Huygens probe took pictures of sedimentary clasts, presumably of ice, on the surface of that moon. Other cold locations could have CO2 ice ("dry ice"): That makes for the sort of rock specimen that would be really difficult to keep on your shelf as a 'deskcrop'...
An additional thought: how could the former presence of icy clasts have influenced the geologic record? Perhaps ice clasts were an integral part of a deposit as it was laid down... but then later the ice melts away. How could we detect and control for this?
That's an image by Chris Waythomas of the USGS, hosted by the Alaska Volcano Observatory website. It shows a cutbank (river-eroded alluvium deposit) along Rust Slough, south of the Drift River Oil Terminal, northeast of Redoubt Volcano. The sediments exposed were deposited on March 22, 2009 by a lahar (volcanic mudflow). The lahar deposit is 2.5 m thick. When I saw this image tonight (as I was searching for another shot), I was particularly struck by the subrounded clasts of ice in the mud. Here is ice acting the part that chunks of rock usually play. Technically, ice is a mineral, and so these chunks are sedimentary clasts much like any other... But to me there's something distinctly different about seeing ice cobbles and pebbles included in a sedimentary deposit. On a planet as warm as Earth, this sort of thing isn't likely to be preserved in the geologic record. It would melt! ...And that gets me thinking about other planets and planet-like objects, like Titan. The Huygens probe took pictures of sedimentary clasts, presumably of ice, on the surface of that moon. Other cold locations could have CO2 ice ("dry ice"): That makes for the sort of rock specimen that would be really difficult to keep on your shelf as a 'deskcrop'...An additional thought: how could the former presence of icy clasts have influenced the geologic record? Perhaps ice clasts were an integral part of a deposit as it was laid down... but then later the ice melts away. How could we detect and control for this?
Labels: alaska, CO2, ice, satellite imagery, sediment, volcano
2 Comments:
One summer when I was working, we brought up a sed core with solid gas hydrate. As the gas dissociates from the sediments with the melting of the ice/increase in pressure, it makes a very distinct texture, it's kind of...frothy? Spongy is what they called it here: http://www.netl.doe.gov/technologies/oil-gas/FutureSupply/MethaneHydrates/projects/DOEProjects/40920_HydrateCenterCore.jpg
While our sediments were fresh, it was pretty easy to point out where the dissociation had taken place, but I imagine there isn't much textural evidence left after consolidation/compaction.
I'd imagine the only signs that might be left were if cavities/vugs left by melting ice were filled in with finer sediment before compaction - which could be detected through geopetal structures. I'm not sure whether formerly ice bearing sediments would be particularly noteworthy in this regard, although it's an interesting thought (especially since I'm working on sequences with allegedly glacial deposits)...
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