In 2018, Kīlauea Volcano experienced its largest lower East Rift Zone (LERZ) eruption and caldera collapse in at least 200 years. After collapse of the Pu‘u ‘Ō‘ō vent on 30 April, magma propagated downrift. Eruptive fissures opened in the LERZ on 3 May, eventually extending ~6.8 kilometers. A 4 May earthquake [moment magnitude (Mw) 6.9] produced ~5 meters of fault slip. Lava erupted at rates exceeding 100 cubic meters per second, eventually covering 35.5 square kilometers. The summit magma system partially drained, producing minor explosions and near-daily collapses releasing energy equivalent toMw4.7 to 5.4 earthquakes. Activity declined rapidly on 4 August. Summit collapse and lava flow volume estimates are roughly equivalent—about 0.8 cubic kilometers. Careful historical observation and monitoring of Kīlauea enabled successful forecasting of hazardous events.

[1] The current eruption at Mount St. Helens is characterized by dome building and shallow, repetitive, long-period (LP) earthquakes. Waveform cross-correlation reveals remarkable similarity for a majority of the earthquakes over periods of several weeks. Stacked spectra of these events display multiple peaks between 0.5 and 2 Hz that are common to most stations. Lower-amplitude very-long-period (VLP) events commonly accompany the LP events. We model the source mechanisms of LP and VLP events in the 0.5-4 s and 8-40 s bands, respectively, using data recorded in July 2005 with a 19-station temporary broadband network. The source mechanism of the LP events includes: 1) a volumetric component modeled as resonance of a gently NNW-dipping, steam-filled crack located directly beneath the actively extruding part of the new dome and within 100 m of the crater floor and 2) a vertical single force attributed to movement of the overlying dome. The VLP source, which also includes volumetric and single-force components, is 250 m deeper and NNW of the LP source, at the SW edge of the 1980s lava dome. The volumetric component points to the compression and expansion of a shallow, magmafilled sill, which is subparallel to the hydrothermal crack imaged at the LP source, coupled with a smaller component of expansion and compression of a dike. The single-force components are due to mass advection in the magma conduit. The location, geometry and timing of the sources suggest the VLP and LP events are caused by perturbations of a common crack system.

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The Yellowstone hotspot resulted from interaction of a mantle plume with the overriding North America plate highly modifying the lithosphere by magmatic-tectonic processes and producing the 17 Ma Yellowstone-Snake River Plain (YSRP) volcanic system. The accessibility of the YSRP has allowed largescale geophysical experiments to seismically image the hotspot and to evaluate its kinematic and dynamic properties using geodetic measurements. Tomography reveals a Yellowstone crustal magma body with 8-15% melt that is fed by an upper-mantle plume extending from 80 km to 660 km deep and tilting 60º west. Contemporary deformation of the Yellowstone caldera is dominated by SW-extension at up to ~3 mm/yr, a fourth of the total Basin-Range opening rate, but with superimposed volcanic uplift and subsidence at decade scales, averaging ~2 cm/yr and unprecedented caldera uplift from 2004-2008 at up to 7 cm/yr. Convection models reveal eastward upper-mantle flow beneath Yellowstone at relatively high rates of 5 cm/yr and opposite in direction to the overriding N. American Plate. This strong flow deflects the ascending plume melt into a tilted configuration, i.e., the plume is caught in a mantle "wind". Dynamic models of the Yellowstone plume revealed relatively low excess temperatures, up to 120°K, with up to 1.5% melt, properties consistent with a weak buoyancy flux of ~0.25 Mg/s. The flux is several times smaller than for oceanic plumes, but it produced a ~600-km wide topographic ~300-m high swell. Employing the plume-geometry we extrapolated the location of the Yellowstone mantle-source southwestward to its initial position at 17 million years beneath eastern Oregon and the southern edge of the LIP Columbia Plateau basalt field suggesting a common origin. Our model suggests that the original plume head rose vertically behind the subducting Juan de Fuca plate, but at ~12 Ma it lost the protection of the subducting plate and encountered cooler, thicker continental lithosphere and became affected by the eastward upper-mantle flow. Regionally, excess gravitation potential energy of the swell drives the SW motion of the YSRP lithosphere that becomes part of a general clockwise rotation pattern of intraplate western U.S. tectonism. Our models thus demonstrate that plume-plate processes of the YSRP have "continentalized" oceanic lithosphere enhancing intraplate extension and highly modifying topography, deep into the continental interior. Our results demonstrate that the dynamic properties of the Yellowstone hotspot deserved its recognition as a "window into the Earth's interior". JVGR

[1] Recently developed UV cameras offer improvement in remote sensing of volcanic SO 2 , with temporal resolutions of ∼1 Hz and synoptic plume views. Integrated UV camera and seismic measurements recorded in January 2009 at Fuego volcano, Guatemala, provide new insight into the system's shallow conduit processes. High temporal resolution SO 2 data reveal patterns of SO 2 emission rate relative to explosions and seismic tremor that indicate tremor and degassing share a common source process. Progressive decreases in emission rate appear to represent inhibition of gas loss from magma as a result of rheological stiffening in the upper conduit. Measurements of emission rate from two closely-spaced vents, made possible by the high spatial resolution of the camera (1024 × 1024 pixels), help constrain this model. This inter-disciplinary approach illuminates eruptive processes at Fuego and holds promise for gaining similar understanding at other volcanic systems.

Fuego volcano, Guatemala is a high (3,800 m) composite volcano that erupts gas-rich, high-Al basalt, often explosively. It spends many years in an essentially open vent condition, but this activity has not been extensively observed or recorded until now. The volcano towers above a region with several tens of thousands of people, so that patterns in its activity might have hazard mitigation applications. We conducted 2 years of continuous observations at Fuego (2005Fuego ( -2007 during which time the activity consisted of minor explosions, persistent degassing, paroxysmal eruptions, and lava flows. Radiant heat output from MODIS correlates well with observed changes in eruptive behavior, particularly during abrupt changes from passive lava effusion to paroxysmal eruptions. A short-period seismometer and two low-frequency microphones installed during the final 6 months of the study period recorded persistent volcanic tremor (1-3 Hz) and a variety of explosive eruptions. The remarkable correlation between seismic tremor, thermal output, and daily observational data defines a pattern of repeating eruptive behavior: 1) passive lava effusion and subordinate strombolian explosions, followed by 2) paroxysmal eruptions that produced sustained eruptive columns, long, rapidly emplaced lava flows, and block and ash flows, and finally 3) periods of discrete degassing explosions with no lava effusion. This study demonstrates the utility of lowcost observations and ground-based and satellite-based remote sensing for identifying changes in volcanic activity in remote regions of underdeveloped countries.

[1] The current activity at Fuego volcano, Guatemala, is characterized by frequent explosions, intermittent lava flows, and persistent degassing. Seismic and infrasound data of explosive activity recorded over 19 days in January 2009 on a temporary broadband network show that explosive intensity is highly variable. However, the seismic expression of the largest explosions includes similar very long period (VLP) earthquakes for each explosion. Waveform modeling in the 10-30 s band constrains the source centroid to a position 300 m below and 300 m west of the summit crater. The calculated moment tensor indicates a volumetric source, which is modeled as a near-vertical dike feeding a SW dipping (35°) sill. The sill is the dominant component, and its projection to the surface nearly intersects the summit crater. The deformation history of the sill is interpreted as (1) an initial inflation that is due to pressurization, followed by (2) a rapid deflation as overpressure is explosively released, and finally (3) a reinflation as fresh magma flows into the sill and degasses. This cycle is attributed to the development of a brittle plug at the top of the magma column and effective sealing of degassing pathways that is due to degassing crystallization as water exsolves and the magma is undercooled. Data from apparent tilt, SO 2 concentrations, and infrasound records support this interpretation. The VLP source location suggests the magma pathway may be migrating westward, which has hazard implications for populations living on the flanks of Fuego.

[1] During the early stages of the [2004][2005][2006][2007][2008] Mount St. Helens eruption, the source process that produced a sustained sequence of repetitive long-period (LP) seismic events also produced impulsive broadband infrasonic signals in the atmosphere. To assess whether the signals could be generated simply by seismic-acoustic coupling from the shallow LP events, we perform finite difference simulation of the seismo-acoustic wavefield using a single numerical scheme for the elastic ground and atmosphere. The effects of topography, velocity structure, wind, and source configuration are considered. The simulations show that a shallow source buried in a homogeneous elastic solid produces a complex wave train in the atmosphere consisting of P/SV and Rayleigh wave energy converted locally along the propagation path, and acoustic energy originating from the source epicenter. Although the horizontal acoustic velocity of the latter is consistent with our data, the modeled amplitude ratios of pressure to vertical seismic velocity are too low in comparison with observations, and the characteristic differences in seismic and acoustic waveforms and spectra cannot be reproduced from a common point source. The observations therefore require a more complex source process in which the infrasonic signals are a record of only the broadband pressure excitation mechanism of the seismic LP events. The observations and numerical results can be explained by a model involving the repeated rapid pressure loss from a hydrothermal crack by venting into a shallow layer of loosely consolidated, highly permeable material. Heating by magmatic activity causes pressure to rise, periodically reaching the pressure threshold for rupture of the ''valve'' sealing the crack. Sudden opening of the valve generates the broadband infrasonic signal and simultaneously triggers the collapse of the crack, initiating resonance of the remaining fluid. Subtle waveform and amplitude variability of the infrasonic signals as recorded at an array 13.4 km to the NW of the volcano are attributed primarily to atmospheric boundary layer propagation effects, superimposed upon amplitude changes at the source.Citation: Matoza, R.