Wednesday, October 22, 2008

Saddle Butte Lake v. West Crater Lake

On my last field trip, I collected high precision GPS points on the highest evidence of overflow that I could find on each likely lava dam. In the case of the Saddle Butte lava dam (SBLD), there is evidence of shallow overflow over most of the extant dam crest...I had not realized this before. There are some photos of this in the recent album I posted. The highest overflow evidence was at 1044m (3425 ft). As for West Crater, the elevation of the first evidence for overflow (rounded basalt cobbles on the extant flow margin) is found at 1029 m (3375 ft)(*note that this is reported incorrectly in the figure caption). There is not nearly as clear a lava dam edifice here as there is at Saddle Butte, you may recall.

For what it is worth, the difference is more than expected or could be read from a topo map. As the figure indicates, a 15 m difference in depth has a locally significant effect on the extent of the lake. This is based, or course, on modern topography.

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