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Extensometer - Aquifer Compaction

Detailed Description

A borehole extensometer is an instrument that measures vertical land motion caused by changes in aquifer thickness. A borehole is drilled through the entirety of an aquifer system and the steel pipe is anchored at the base to the basement rock. Aquifer compaction is measured by the change in the length of the extensometer pipe which protrudes above the ground surface.

When an aquifer compacts and the land surface subsides, more of the static extensometer pipe protrudes above ground. Meanwhile, the instrument table sinks along with the land surface. This change is measured and recorded by instruments such as linear potentiometers.

Based on the USGS extensometer at Nansemond, Virginia (USGS 365337076251606 59D 39).


Public Domain.