Cordilleran Section - 115th Annual Meeting - 2019

Paper No. 11-11
Presentation Time: 9:00 AM-6:00 PM


WARREN, Sondra M., ERNST, Brianna M. and LUNDBLAD, Steven P., Dept. of Geology, Univ. of Hawaii at Hilo, 200 W. Kawili St., Hilo, HI 96720

The Koaʻe fault system is located south of the Kīlauea volcano summit on Hawai`i Island. It consists of thousands of ground cracks and is actively widening. The fault system runs ENE, is approximately 11 km long and 2-3 km wide. Measurements taken over the past 50 years show the Koaʻe fault system as a whole was widening at an average rate of ~4.5 cm per year. Individual faults move 1-5 mm per year. After the 2018 Kīlauea eruption, we remeasured the stations to establish a new baseline for future deformation. Movement along faults in the Koa’e system were significantly higher (cms to 10s of cms on individual faults) as a result of the 2018 Kīlauea eruption events.

Accompanying the eruption of ~1 billion cubic meters of lava that occurred in the Lower East Rift Zone (LERZ) covering ~35.5 square km, were a series of 62 collapse events at the Kīlauea summit and a M6.9 EQ centered beneath the south flank of the volcano. Collapse was likely caused by partial draining of the shallow summit magma chamber, as the volume of collapse is on the same order of magnitude as the volume of lava erupted in the LERZ. In the aftermath of the summit-area deformation, we measured 20 of the USGS-HVO crack stations from a network originally installed in the 1960s.

Beginning in September 2018 we measured relative motion across the cracks using the same methodology as past surveys, namely steel tape for horizontal distances and high-precision (approximating second order) line-leveling for elevation differences. Data was compared with that collected at irregular intervals over the past 20-50 years. Response along the Koa’e fault zone to collapse events at the summit varied with location showing both extension and compression on individual faults. The Kulanaokuaiki Pali, which is the southernmost fault, shows the largest amount of movement. Displacement increases from east to west along the pali. Horizontal extension ranges from 1.7 cm to 13.9 cm, while vertical displacement ranges from 3.2 cm to 17.3 cm. Total extension along the Koa`e system in this area ranges from 4.5 cm to 27 cm. This is an order of magnitude larger than past measurements along the fault.