![]() The summit of Mauna Loa inflated during 2014–2020 at a rate of up to 6 cm/year in radar line-of-sight (LOS) direction (Fig. A 1950 flow reached the populated coastal area in 2–3 h after the eruption began 15.Īscending and descending Cosmo-Skymed InSAR time-series and daily GPS positions provide records about the changing deformation sources. Mauna Loa’s principal hazards are lava flows. Since the last eruption in 1984, the volcano has had at least two inflation periods 10, 13, one of them associated with deep (> 35 km) seismicity 14. There is stress feedback between rift intrusion and decollement motion, with one encouraging the other and vice versa 12. Mauna Loa, the largest volcano on Earth, grows by lava flows at the surface, by repeated magma intrusions into the southwest rift zone (SWRZ) and northeast rift zone (NERZ) and by seismic and aseismic motion along a low-angle, upward-dipping basal decollement fault under the volcanic pile 11. Here we demonstrate that Mauna Loa’s dike-like magma body evolves in response to changes in the pressurization rate, and that this response is shaped by topographic stresses and stress perturbations due to decollement slip, offering the opportunity to use stress field information for hazard assessment. Yet these studies were conducted after eruptions. Examples include, the encouragement and suppression of shallow magma accumulation under collapse calderas and volcanic edifices, respectively 4, 5, 6, the alignment of propagating dikes to the regional stress field immediately after dike injection 7, twisting of propagating sills to dikes due to unloading stresses from caldera collapse 5, in some settings widening of dikes in areas of reduced loading stress because of low topography 8‚ and dike intrusions following stress gradients due to previous intrusions and earthquakes 9, 10. One of the most significant advances in volcanology in the past decade are observations showing that the subsurface accumulation and migration of magma follows gradients in the stress field, following concepts of dike emplacement and growth put forward by Anderson 1, Delaney et al. Overall, the magma body widened about 4.5 m during 2002–2020. The evolution of the dike-like magma body including the reduction in vertical extent is consistent with a slowly ascending dike propagating laterally when encountering a stress barrier and freezing its tip when magma influx waned. Geodetic inversions reveal a 8 × 8.5, 10 × 3 and 9 × 4 km 2 dike-like magma body during the 2014–2015, 2015–20–2020 periods, respectively, and an average decollement slip of ~ 23 cm/year along a 10 × 5 km 2 fault. ![]() In 2017, deformation migrated back, and inflation continued at the pre-2015 location. Volcanoes commonly respond to magma pressure increase with the injection of a dike, but Mauna Loa responded with lateral growth of its magma body in the direction of decreasing topographic stress. The intrusion started after at least 4 years of decollement slip under the eastern flank creating > 0.15 MPa opening stresses in the rift zone favorable for magma intrusion. Space-geodetic observations of a new period of inflation at Mauna Loa volcano, Hawaii, recorded an influx of 0.11 km 3 of new magma into it’s dike-like magma body during 2014–2020.
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