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] We present a reliable methodology to estimate the energy associated with the subaerial diffuse degassing of volcanic-hydrothermal fluids. The fumaroles of 15 diffuse degassing structures (DDSs) located in eight volcanic systems in the world were sampled and analyzed. Furthermore, each area was measured for soil temperature gradients and for soil CO 2 fluxes. The results show that each hydrothermal or volcanic system is characterized by a typical source fluid which feeds both the fumaroles and diffuse degassing through the soil. Experimental data and the results of physical numerical modeling of the process demonstrate that the heat released by condensation of steam at depth is almost totally transferred by conduction in the uppermost part of the soil. A linear relationship is observed between the log of the steam/gas ratio measured in the fumaroles and the log of the ratio between soil thermal gradient and soil-gas flux. The main parameter controlling this relation is the thermal conductivity of the soil (K c ). For each area, we computed the values of K c which range from 0.4 to 2.3 W m À1°CÀ1 . Using the CO 2 soil fluxes as a tracer of the deep fluids, we estimated that the total heat released by steam condensation in the systems considered varies from 1 to 100 MW.

[1] Two methods are used to estimate CO 2 degassing from the Yellowstone magmatic-hydrothermal system. The amount of magmatic CO 2 released as basaltic magma emplaces from the mantle into the crust beneath the Yellowstone caldera is calculated and compared to CO 2 fluxes measured in three different types of hydrothermal regions within Yellowstone. Comparison of modeled estimates with surface measurements suggests that 3.7 ± 1.3 Â 10 11 mol y À1 (45 ± 16 kt d À1) of CO 2 are released from Yellowstone due to diffuse degassing. Flux measurements suggest that the diffuse flux in acid-sulfate regions is significant in total calculations (>96% of the total), whereas the diffuse flux in neutral-chloride and travertine-precipitating areas is not significant. Analyses of carbon and helium isotopes suggest that $50% of the CO 2 emitted is derived from sedimentary sources at locations outside the caldera, whereas locations inside the caldera likely have sedimentary contributions <30%. In addition to release of CO 2 with emplacement, magma crystallization in the subsurface is thought to contribute significantly to the CO 2 emissions at the surface. The contribution of CO 2 from Yellowstone to global volcanic CO 2 emissions ($6-7 Â 10 12 mol y À1 ) is comparable to the CO 2 contribution from other large volcanic systems like Popocatepetl, Mexico and the combined contribution from the Hawaii hot spot. Likewise, the amount of CO 2 emitted per land area from Yellowstone (on average 10 8 mol CO 2 km À2 y À1) is comparable to other large volcanic and hydrothermal systems worldwide.

Volcanoes are the main pathway to the surface for volatiles that are stored within the Earth. Carbon dioxide (CO2) is of particular interest because of its potential for climate forcing. Understanding the balance of CO2 that is transferred from the Earth’s surface to the Earth’s interior, hinges on accurate quantification of the long-term emissions of volcanic CO2 to the atmosphere. Here we present an updated evaluation of the world’s volcanic CO2 emissions that takes advantage of recent improvements in satellite-based monitoring of sulfur dioxide, the establishment of ground-based networks for semi-continuous CO2-SO2 gas sensing and a new approach to estimate key volcanic gas parameters based on magma compositions. Our results reveal a global volcanic CO2 flux of 51.3 ± 5.7 Tg CO2/y (11.7 × 1011 mol CO2/y) for non-eruptive degassing and 1.8 ± 0.9 Tg/y for eruptive degassing during the period from 2005 to 2015. While lower than recent estimates, this global volcanic flux implies that a significant proportion of the surface-derived CO2 subducted into the Earth’s mantle is either stored below the arc crust, is efficiently consumed by microbial activity before entering the deeper parts of the subduction system, or becomes recycled into the deep mantle to potentially form diamonds.