Inflation/Deflation Cycles During the 2015 Activity of Fuego Volcano, Guatemala

Abstract:

Fuego is an active stratovolcano located 16 km west of the city of Antigua, Guatemala. It forms a part of a chain of volcanoes that are located within the Central American Volcanic Arc. Predominantly, the volcano exhibits vulcanian and strombolian eruptions with basalt to basaltic-andesite lava flows. Short-term studies with temporary broadband seismic stations deployed near the summit documented clear pre-eruption tilt signals. In these studies, tilt was derived from the horizontal components at periods below the instrument corner. The tilt was interpreted to reflect summit inflation beginning 20-30 minutes before the explosions.

In our study, we analyze the data recorded by a tiltmeter that was installed ~800 m north of the summit vents. The data was collected over a period of three and a half months from late September 2015 to mid-January 2016, providing a longer-term dataset than prior tilt studies at Fuego. We implemented template matching to identify the repetitive tilt signals. Two remarkable features of the earlier seismically-derived tilt studies are confirmed: the tilt starts 20 - 30 minutes before the onset of eruption and flattens or reverses in direction 1-2 minutes prior to the eruption; and the direction of maximum tilt is nearly tangential and perpendicular to the ridge that trends north from the Fuego summit. The maximum tilt occurs in the positive east direction at 0.45 microradians and is nine times greater than the tilt in the north direction. The tilt signals indicate that the rate of inflation is significantly larger than the deflation. Observations of pre-explosion tilt highlight a quasi-cyclic nature of Fuego activity. The relatively long-term record of tilt allows for a description of changes in eruption style, where days to weeks of less frequent explosions build to periods of more frequent, more explosive eruptions with short-lived lava flows approximately monthly.