VOLCANO MADNESS: Re: [Geology2] Re: Nearly 3,900 New Maps in Time for Summer

Friday, August 2, 2013

Re: [Geology2] Re: Nearly 3,900 New Maps in Time for Summer

Thanks for the follow-up comment!

On Thu, Aug 1, 2013 at 10:59 AM, Clay Chesney <fossrme@yahoo.com> wrote:

Talking about grabens reminds me of some research work that a prof was doing at one of the colleges where I taught. He would spend hours in the basement of the geology building creating physical models of geologic structures. One of his most interesting ones simulated horst and graben structure by using simple wooden blocks floating in water. He cut a 2x4 crosswise with angled cuts to make v-shaped wedges, half of them pointing up and half pointing down. When the board, cut this way, was put into water the wedges with the broad base floated upwards and the ones with the broad side on top moved down. It was a very simple demonstration that vertical movement on landmasses doesn't require vertical tectonic forces; if the crust is fractured in the right way the blocks will move up or down because they are resting on a plastic zone below and isostasy will cause them to adjust vertically.

I thought this was a clever illustration of how isostasy works and how something like the basin-and-range area of the western US formed. The professor, John Sales, went off to work for one of the oil companies and I never heard of him again, which is probably to be expected because I didn't work in the area of structural geology. His model really belonged with the earlier era of structural geology that dealt with forces and land movements in the broadest sense. By the time he developed it the science had moved on to more sophisticated analysis, but I think he added something important to the basic understanding of how and why crustal units move. I would be interested to know if that conceptual model became embedded in the science.