Groundwater level changes in a deep well in response to a magma intrusion event on Kilauea Volcano, Hawai'i

[1] On May 21, 2001, an abrupt inflation of Kilauea Volcano's summit induced a rapid and large increase in compressional strain, with a maximum of 2 μstrain recorded by a borehole dilatometer. Water level (pressure) simultaneously dropped by 6 cm. This mode of water level change (drop) is in contrast to that expected for compressional strain from poroelastic theory, and therefore it is proposed that the stress applied by the intrusion has caused opening of fractures or interflows that drained water out of the well. Upon relaxation of the stress recorded by the dilatometer, water levels have recovered at a similar rate. The proposed model has implications for the analysis of ground surface deformation and for mechanisms that trigger phreatomagmatic eruptions.