1. Department of Geophysics, Mitchell Building, Stanford University, Stanford, California 94305-2215, USA
2. US Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, Hawaii 96718, USA
3. US Geological Survey, Cascades Volcano Observatory, 5400 MacArthur Blvd, Vancouver, Washington 98661, USA

Correspondence to: Peter Cervelli^1,2 Correspondence and requests for materials should be addressed to P.C. (e-mail: Email: cervelli@sumo.wr.usgs.gov).

One of the greatest hazards associated with oceanic volcanoes is not volcanic in nature, but lies with the potential for catastrophic flank failure^{1, 2}. Such flank failure can result in devastating tsunamis and threaten not only the immediate vicinity, but coastal cities along the entire rim of an ocean basin³. Kilauea volcano on the island of Hawaii, USA, is a potential source of such flank failures^{3, 4} and has therefore been monitored by a network of continuously recording geodetic instruments, including global positioning system (GPS) receivers, tilt meters and strain meters. Here we report that, in early November 2000, this network recorded transient southeastward displacements, which we interpret as an episode of aseismic fault slip. The duration of the event was about 36 hours, it had an equivalent moment magnitude of 5.7 and a maximum slip velocity of about 6 cm per day. Inversion of the GPS data reveals a shallow-dipping thrust fault at a depth of 4.5 km that we interpret as the down-dip extension of the Hilina Pali–Holei Pali normal fault system. This demonstrates that continuously recording geodetic networks can detect accelerating slip, potentially leading to warnings of volcanic flank collapse.