Iceberg size and transport distance
This image came to my attention the other day via Lutz's Geoberg blog. It's one of the high-res images provided by the newly-launched satellite, the GeoEye-1, which is supplying new images to Google*. The image shows a marginal lake associated with an alpine glacier in Kenai Fjords National Park, Alaska (just south of Seward):
The top of the above image is not north; it's southwest. Mentally rotate it, and you can see that the resolution is a lot better than the current level on Google Earth and Google Maps:
The thing that struck me about the new GeoEye image, aside from its beauty, is the distinct pattern of iceberg sizes in the lake: freshly calved off the glacier, the biggest icebergs are close to their source, while further away the icebergs are smaller. This pattern struck me as being analogous to sediment. Fresh from its source, sedimentary particles are at their largest size, and the further away they travel, the more weathering they experience. This weathering (in particular of the physical variety) tends to break them down into smaller pieces. Adjacent to an orogenic belt, for instance, you tend to find deposition of sedimentary particles shed off the uplifting mountains. As a general rule, these are of the largest sizes and the greatest volume closest to the source, and then particle size and stratum thickness both diminish with increasing distance from the orogen.
For a North American example, consider the Catskill Clastic Wedge, a tick pile of sediments shed off the late Devonian Acadian Orogeny along the east coast. Here's a cross-sectional view** (pre-Alleghany Orogeny deformation) of the wedge, running from the Bay of Fundy west to Michigan:
Same pattern! Coarse stuff, and more volume of stuff, close to the source. Finer stuff, and less volume of stuff, further from the source. Just like the iceberg, except the weathering of the icebergs is mainly thermal, while the weathering of the sediments is physical, accompanied by depositional sorting by the transporting currents of water.
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* An original version of this post misidentified Google as the owners of the GeoEye-1, as opposed to the company called GeoEye, which sells images to Google. Thanks to Bruce Haley for the correction. (updated 8:14AM eastern time on Dec. 9, 2008)
** Image redrawn (by me) from an original in Prothero & Dott (2003).
The top of the above image is not north; it's southwest. Mentally rotate it, and you can see that the resolution is a lot better than the current level on Google Earth and Google Maps:
The thing that struck me about the new GeoEye image, aside from its beauty, is the distinct pattern of iceberg sizes in the lake: freshly calved off the glacier, the biggest icebergs are close to their source, while further away the icebergs are smaller. This pattern struck me as being analogous to sediment. Fresh from its source, sedimentary particles are at their largest size, and the further away they travel, the more weathering they experience. This weathering (in particular of the physical variety) tends to break them down into smaller pieces. Adjacent to an orogenic belt, for instance, you tend to find deposition of sedimentary particles shed off the uplifting mountains. As a general rule, these are of the largest sizes and the greatest volume closest to the source, and then particle size and stratum thickness both diminish with increasing distance from the orogen.
For a North American example, consider the Catskill Clastic Wedge, a tick pile of sediments shed off the late Devonian Acadian Orogeny along the east coast. Here's a cross-sectional view** (pre-Alleghany Orogeny deformation) of the wedge, running from the Bay of Fundy west to Michigan:
Same pattern! Coarse stuff, and more volume of stuff, close to the source. Finer stuff, and less volume of stuff, further from the source. Just like the iceberg, except the weathering of the icebergs is mainly thermal, while the weathering of the sediments is physical, accompanied by depositional sorting by the transporting currents of water.
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* An original version of this post misidentified Google as the owners of the GeoEye-1, as opposed to the company called GeoEye, which sells images to Google. Thanks to Bruce Haley for the correction. (updated 8:14AM eastern time on Dec. 9, 2008)
** Image redrawn (by me) from an original in Prothero & Dott (2003).
Labels: alaska, analogies, art, canada, glacial landforms, glaciation, maine, michigan, mountains, new york, satellite imagery, sediment
3 Comments:
There may be something to your observation, but I don't think this locality is the best test of the hypothesis. Because the body of water in this view is a lake which presumably shallows towards its margins, I would imagine that the larger bergs would ground themselves before they could get very far from the terminus of the glacier - after all 9/10 of the ice is below the surface. A better test would be to see the distribution of bergs in a deep water fjord.
Excellent point. Plus it's just a lake, not an elongated feature (like a fjord) more akin to a lake.
Need to correct your second sentence, "It's one of the high-res images provided by Google's new satellite, the GeoEye."
The satellite is not Google's. The name of the satellite is GeoEye-1 which is owned by GeoEye. Google buys images from GeoEye. Have a great day.
Bruce Haley
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