Maunaloa This Week, April 16, 2021

Despite being more visible than the erupting Kīlauea on mainland news, Maunaloa is not erupting. USGS Hawaiian Volcano Observatory reports “no significant change in deformation rates or patterns that would indicate increased volcanic hazard at this time.” Last week on Maunaloa: -GPS distance across summit switches to extension, from temporary contraction since end of March -Ground tilt shows a small, but similar change -No SO2 emissions, fumarole temperatures stable below 100 degrees C / 212 deg F -220 small-magnitude earthquakes, all less than M2.5, 188 of them below the summit and upper-elevation flanks at depths of less than 8 km / 5 mi below ground level -Earthquakes spike 1 week ago on April 9 with ~70 events, otherwise all days since show background levels below ~30 events per day Monitoring signals and recent InSAR imagery suggest that magma continues to fill slowly underground (Figure 2), triggering the observed seismic adjustments on Maunaloa’s flanks over the past few weeks. Cycles of summit filling and flank adjustment are common on the volcano, and a switch back to the filling phase is consistent with GPS data. It would not be surprising to see the return of shallow seismicity around the volcano’s summit, along with some reduction of flank adjustment earthquakes in the short term, until the cycle repeats. For now, the deformation rates are not indicative of any rapid or imminent change towards an eruption on Maunaloa. Live video review of Maunaloa signals is broadcast at 5pm HST Fridays and archived, along with short video updates, on this channel - including monitoring signals, photos & videos, time-lapses, geologic context and annotation, and discussion of live viewer questions. #Maunaloa Figure 1: Capture from Maunaloa summit webcam courtesy of USGS-HVO on April 16, 2021, showing traces of recent snowfall. Figure 2: This image of the summit of Mauna Loa Volcano is derived from satellite-based interferometric synthetic aperture radar (InSAR) and is called an interferogram. Each cycle of colors from blue to green represent a change in the distance between the ground and the satellite (range change) of 1.55 cm. Interferograms are constructed from radar images taken on two different dates and show the amount deformation that occurred between the two acquisition dates. This image shows the overall inflation of Mauna Loa’s summit that occurred from November 2020 to March 2021. It also shows several fringes (color cycles) consistent with subsidence inside Moku‘āweoweo caldera and related to a shallow earthquake that was recorded on March 6, 2021. The red circles show the locations of earthquakes associated with that event as determined by HVO’s seismic network. Recent contraction that has been recorded on summit GPS stations has not yet been identified in any interferograms. (Image & caption: USGS-HVO)