Volcano dome dynamics at Mount St. Helens: Deformation and intermittent subsidence monitored by seismicity and camera imagery pixel offsets

Abstract

The surface deformation field measured at volcanic domes provides insights into the effects of magmatic processes, gravity‐ and gas‐driven processes, and the development and distribution of internal dome structures. Here we study short‐term dome deformation associated with earthquakes at Mount St. Helens, recorded by a permanent optical camera and seismic monitoring network. We use Digital Image Correlation (DIC) to compute the displacement field between successive images and compare the results to the occurrence and characteristics of seismic events during a 6 week period of dome growth in 2006. The results reveal that dome growth at Mount St. Helens was repeatedly interrupted by short‐term meter‐scale downward displacements at the dome surface, which were associated in time with low‐frequency, large‐magnitude seismic events followed by a tremor‐like signal. The tremor was only recorded by the seismic stations closest to the dome. We find a correlation between the magnitudes of the camera‐derived displacements and the spectral amplitudes of the associated tremor. We use the DIC results from two cameras and a high‐resolution topographic model to derive full 3‐D displacement maps, which reveals internal dome structures and the effect of the seismic activity on daily surface velocities. We postulate that the tremor is recording the gravity‐driven response of the upper dome due to mechanical collapse or depressurization and fault‐controlled slumping. Our results highlight the different scales and structural expressions during growth and disintegration of lava domes and the relationships between seismic and deformation signals.

Load Stress Controls on Directional Lava Dome Growth at Volcán de Colima, Mexico

“…Dome growth at Soufrière Hills, Montserrat, between 1995 and 1998 produced several oblique spines in different directions (Watts et al, 2002). Similar observations were made during the 2004-2006 dome extrusion of Mount St. Helens, USA, which also produced directional spines likely originating from the same vent (Vallance et al, 2008), episodically extruding, spreading and sliding laterally (Walter, 2011;Salzer et al, 2016). At Chaiten, Chile, such spines eventually collapsed in 2008 and produced far reaching PDCs (Pallister et al, 2013b).…”

The Relationship Between Lava Fountaining and Vent Morphology for the 2014–2015 Holuhraun Eruption, Iceland, Analyzed by Video Monitoring and Topographic Mapping

“…To monitor eruption sites and venting activity at high spatial and temporal resolution, video monitoring and computer vision tools (i.e., quantitative video analysis tools) are essential. Volcano monitoring has been achieved with thermal cameras (e.g., James et al, 2006;Patrick et al, 2007;Stevenson and Varley, 2008), highspeed cameras (e.g., Taddeucci et al, 2012b), and time-lapse cameras (Walter, 2011;Salzer et al, 2016). These observations have been made from safe distances at various types of volcanoes, such as at Etna, Italy (e.g., Behncke et al, 2006;Scollo et al, 2014), Stromboli, Italy (e.g., Andronico et al, 2013), Mount Saint Helens, USA (Major et al, 2009), and Kilauea, Hawai'i (e.g., Patrick et al, 2010).…”

Absence of Detectable Precursory Deformation and Velocity Variation Before the Large Dome Collapse of July 2015 at Volcán de Colima, Mexico

“…The integration of new observations and analysis methods to the monitoring system may also help detecting forthcoming eruptions. For example, pixel offsets tracking methods applied to optical images acquired at small distance from the dome might bring useful information regarding the dome growth rate (Salzer et al, 2016) while high resolution SAR images can provide information on the dome deformation in quiescent periods (Salzer et al, 2017). Indeed, a hypothetical observation of both summit deformation and velocity variations, with amplitude larger than the usual fluctuations (i.e., >0.2%) and not related with strong tectonic earthquakes, could indicate a possible impending eruption and should be taken into account by the warning system of Volcán de Colima.…”