Do corners move?
I’ve been asked that a few times and my answer is a conditional yes.
So I’m doing a survey right now that is in lowlands along a large river. Ground is mostly glacial silt and wind blown loess. Some of the best farmland in the State of Alaska. I have work in the area going back to 2004 but the most recent work in the area was done in 2016/2017. As a side, it’s along the 4th Standard Parallel so staggered sections. Not many of the original GLO 1914 corners remain. I went back this week and using the same control point for the base, found I was missing everything tied in the area by .3-.4′ in a north/south direction. First inclination was that our control point had been disturbed. A lengthy static session showed it to be stable with very little discrepancy from past sessions. So what gives? Well, as best I can figure, back on November 30, 2018, we had a 7.1 earthquake and given the water saturated soils, as far as I can tell, that entire body of land moved south a bit under half a foot. Kind of cool having a ring side seat and being in a position to be able to actually measure that change. In other areas some distance from this location, I’ve had control points that were shifted, I assume by the same quake, by upwards a foot horizontally. Terra firma ain’t all that firm.
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