To measure deformation over a large area at an active volcano, instruments and techniques are borrowed from surveying and geodesy. We discuss several methods employed at the Cascades Volcano Observatory for installing bench marks and reflector prisms used to measure deformation. We emphasize a versatile system designed for ease of portability, compatibility of components, and quick and easy installation on restless volcanoes.
Instrument bench marks and reflector prisms are installed into bedrock by drilling holes or into unconsolidated substrate by constructing concrete foundations.
Backsights, lines measured away from the volcano to areas presumed more stable, are used to test the stability of EDM bench marks and are included in deformation networks to provide a means of checking the relative stability of the bench marks. Careful site selection, building as much redundancy as is practical into deformation networks, and frequent measurements provide a check on reflector site stability.
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