Monday, December 9, 2013

Gopher Camp and Mima Mounds

The gopher camp for Mima Mound formation has another paper out Biotic origin of Mima Mounds supported by numerical modeling.

Mima Mounds are named for Washington States Mima Praire south of Olympia. However, Mima Mounds are found in many other areas including extensive areas in eastern Washington. They have been driving geologists crazy for 100 years or more.

Gophers have been suggested for the formation of the mounds. Not a single gopher wanting to build a large mound, but multiple generations of gophers moving soil in a preferential manner as described in the paper linked above. The idea has been around for some time and for many mound sites it makes sense and actually seems very likely. However, the Mima Mound Prairie itself as well as other nearby prairies in southwest Washington with and without mounds presents some still unresolved challenges to the gopher camp.

There are still other competing theories for the southwest Washington prairies and some relatively new information on the the geology of the underlying gravel units (Goldstein, Pringle and Futornick, 2002).

(Washburn, 1988) provides an excellent overview of the Mima Prairie and other nearby prairies and has a matrix of the various proposals for mound formation which leans to a sediment anchoring model. Given the newer data and particularly the LiDAR imagery of the southwest Washington prairies a revised matrix after Washburn might be an interesting exercise.       


magmatist said...

Yur post on the new 'gopherist' article is thought provoking. You conclude by calling for a renewed matrix of causes. I include such an updated matrix in the Mima Mounds chapter in my book, Geology Underfoot in Western Washington.
The book should be out in early fall 2014.
Dave Tucker

susan said...

I wonder why there has to be only one origin for mima mounds. I like the seismic explanation for some of them. Maybe gophers for others. Perhaps peri-glacial where it might apply (not Texas, e.g.)

Dan McShane said...

DT: Looking forward to that book and your take on the matrix.
Susan: I am in the various explanations camp and strongly suspect part of the challenge is that multiple factors are at play for some mound sites. At the very least some thought must be given to other soil moving forces than simply one. One reason the gopher theory is appealing is it provides a counter force to soil moving processes that would destroy the mounds. But as you note, Texas is a lot different than say the high plains of eastern Washington which is in turn a lot different that the gravel prairies of southwest Washington.