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.

Caldera-forming eruptions are among Earth’s most hazardous natural phenomena, yet the architecture of subcaldera magma reservoirs and the conditions that trigger collapse are poorly understood. Observations from the formation of a 0.8–cubic kilometer basaltic caldera at Kīlauea Volcano in 2018 included the draining of an active lava lake, which provided a window into pressure decrease in the reservoir. We show that failure began after <4% of magma was withdrawn from a shallow reservoir beneath the volcano’s summit, reducing its internal pressure by ~17 megapascals. Several cubic kilometers of magma were stored in the reservoir, and only a fraction was withdrawn before the end of the eruption. Thus, caldera formation may begin after withdrawal of only small amounts of magma and may end before source reservoirs are completely evacuated.

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For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit http://www.usgs.gov or call 1-888-ASK-USGS (1-888-275-8747) For an overview of USGS information products, including maps, imagery, and publications, visit http: //www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.Suggested citation: Poland, M.P., Takahashi, T.J., and Landowski, C.M., eds., 2014, Characteristics of Hawaiian volcanoes: U.S. Geological Survey Professional Paper 1801, 428 p., http://dx.doi.org/10.3133/pp1801. ForewordThe Hawaiian Islands and their volcanoes have featured prominently in the history of the United States Geological Survey (USGS) nearly back to the 1879 founding of the organization. In 1882, USGS Director John Wesley Powell sent Captain Clarence E. Dutton, an officer in the United States Army who was detailed to the USGS, to Hawai'i-then still an independent kingdom-to study its volcanic geology in preparation for mapping in the Cascade Range. Dutton was an inspired choice for the assignment. He was already well known for his explorations in the western United States, thanks in large part to his vivid written accounts of the Grand Canyon region, and his observations of the volcanoes, land, and people of Hawai'i after 4 months of field work (published as part of the "4th Annual Report of the U.S. Geological Survey" in 1884) are no less engaging. Dutton's experience in Hawai'i was a great aid to his subsequent assignment as the head of the USGS Division of Volcanic Geology, which mapped volcanoes throughout California, Oregon, Washington, Utah, Arizona, and New Mexico. USGS work in Hawai'i subsequently shifted toward water resources, especially as related to agricultural development. In 1909, USGS geologist Walter Mendenhall toured the islands and established a framework for systematic observations that were eventually assumed by what had become the Territory of Hawaii. In 1919, the Territory requested a comprehensive assessment of the geology and water resources of the entire island chain. One of the main participants in this work was USGS geologist Harold T. Stearns. Over the ensuing 30 years, Stearns published 12 comprehensive reports (Hawaii Division of Hydrography Bulletins) covering the characteristics of every major Hawaiian island (except Kauai, which was covered in 1960 in volume 13 by another longtime USGS geologist, Gordon Macdonald). The work of Stearns and his colleagues has stood the test of time and is still an important resource for geologists working throughout the State.In 1924, the USGS took over operation of th...

The results of geodetic monitoring since 2002 at Sierra Negra volcano in the Galápagos Islands show that the filling and pressurization of an ϳ2-km-deep sill eventually led to an eruption that began on 22 October 2005. Continuous global positioning system (CGPS) monitoring measured Ͼ2 m of accelerating inflation leading up to the eruption and contributed to nearly 5 m of total uplift since 1992, the largest precursory inflation ever recorded at a basaltic caldera. This extraordinary uplift was accommodated in part by repeated trapdoor faulting, and coseismic CGPS data provide strong constraints for improved deformation models. These results highlight the feedbacks between inflation, faulting, and eruption at a basaltic volcano, and demonstrate that faulting above an intruding magma body can relieve accumulated strain and effectively postpone eruption.

Sierra Negra volcano began erupting on 22 October 2005, after a repose of 26 years. A plume of ash and steam more than 13 km high accompanied the initial phase of the eruption and was quickly followed by a~2-kmlong curtain of lava fountains. The eruptive fissure opened inside the north rim of the caldera, on the opposite side of the caldera from an active fault system that experienced an m b 4.6 earthquake and~84 cm of uplift on 16 April 2005. The main products of the eruption were an`a`a flow that ponded in the caldera and clastigenic lavas that flowed down the north flank. The`a`a flow grew in an unusual way. Once it had established most of its aerial extent, the interior of the flow was fed via a perched lava pond, causing inflation of the`a`a. This pressurized fluid interior then fed pahoehoe breakouts along the margins of the flow, many of which were subsequently overridden by`a`a, as the crust slowly spread from the center of the pond and tumbled over the pahoehoe. The curtain of lava fountains coalesced with time, and by day 4, only one vent was erupting. The effusion rate slowed from day 7 until the eruption's end two days later on 30 October. Although the caldera floor had inflated by~5 m since 1992, and the rate of inflation had accelerated since 2003, there was no transient deformation in the hours or days before the eruption. During the 8 days of the eruption, GPS and InSAR data show that the caldera floor deflated~5 m, and the volcano contracted horizontally~6 m. The total eruptive volume is estimated as being~150×10 6 m 3 . The opening-phase tephra is more evolved than the eruptive products that followed. The compositional variation of tephra and lava sampled over the course of the eruption is attributed to eruption from a zoned sill that lies 2.1 km beneath the caldera floor.

After 53 years of quiescence, Mount Agung awoke in August 2017, with intense seismicity, measurable ground deformation, and thermal anomalies in the summit crater. Although the seismic unrest peaked in late September and early October, the volcano did not start erupting until 21 November. The most intense explosive eruptions with accompanying rapid lava effusion occurred between 25 and 29 November. Smaller infrequent explosions and extrusions continue through the present (June 2019). The delay between intense unrest and eruption caused considerable challenges to emergency responders, local and national governmental agencies, and the population of Bali near the volcano, including over 140,000 evacuees. This paper provides an overview of the volcanic activity at Mount Agung from the viewpoint of the volcano observatory and other scientists responding to the volcanic crisis. We discuss the volcanic activity as well as key data streams used to track it. We provide evidence that magma intruded into the mid-crust in early 2017, and again in August of that year, prior to intrusion of an inferred dike between Mount Agung and Batur Caldera that initiated an earthquake swarm in late September. We summarize efforts to forecast the behavior of the volcano, to quantify exclusion zones for evacuations, and to work with emergency responders and other government agencies to make decisions during a complex and tense volcanic crisis.

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