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This paper is the first to compile the accounts of Western explorers to Hawai'i who used volcanic heat. During the 1800s, Western explorers used volcanic heat when climbing and surveying Kīlauea and Mauna Loa volcanoes in Hawai'i. The explorers cooked food on steam vents and lava streams. They drank condensed water from volcanic steam and bathed in a warm basin and warm springs. They warmed themselves near steam cracks and a lava stream, lit cigarettes with Kīlauea's lava lake, and collected rocks. To confirm the presence of volcanic heat, this study uses geothermal resource maps and data from the Hawai'i Play Fairway project. The areas where the explorers used volcanic heat have a probability of volcanic heat of 0.7 to 1.0, and elevated temperatures in nearby water wells indicate heat sources. Kīlauea and Mauna Loa erupted numerous times, and the surrounding areas experienced volcanic steam releases and lava flows. The explorers used volcanic heat to facilitate not only their survival but also the Western exploration and scientific investigation of Kīlauea and Mauna Loa volcanoes. [ABSTRACT FROM AUTHOR]

"Surges" in magma supply from the mantle can lead to significant changes in eruptive behavior, thus their early identification is critical to long‐term eruption forecasting. Here, we document and analyze two order‐of‐magnitude increases in seismicity in the upper mantle beneath southern Hawaiʻi between 2015 and 2020. We interpret the anomalous seismicity, which involved the rapid formation of new multiplets and a change in fault‐plane solution orientations relative to pre‐2015 events, as reflecting a substantial increase, or "surge" in mantle‐derived magma, and we suggest that the intruded magma has been driving concurrent unrest at Mauna Loa, Kīlauea, and Lōʻihi Volcanoes through mechanical stress transfer. Plain Language Summary: The rate of earthquakes in the upper mantle beneath the southern part of the Island of Hawaiʻi increased strongly in 2015, and again in 2019. The characteristics of the earthquakes that occurred between 2015 and 2020 indicate that they are caused by the emplacement of new magma deep beneath Hawai'i. The timing of unrest at the neighboring volcanoes Kīlauea, Mauna Loa, and Lōʻihi is coincident with the increases in deep earthquake activity, indicating that the newly emplaced magma is squeezing the plumbing systems of the neighboring volcanoes and causing them to deform and have more shallow earthquakes. Key Points: The rate of deep earthquakes beneath southern Hawai'i increased significantly in 2015, and again in 2019The 2015–2020 deep earthquakes are consistent with magma intrusionIncreases in seismicity are coincident with unrest at Mauna Loa, Kīlauea, and Lōʻihi Volcanoes, indicating a possible causal relationship [ABSTRACT FROM AUTHOR]

Ferric/ferrous ratios have been used to estimate the oxygen fugacity of lavas erupted in 1984 on Mauna Loa Volcano, Hawaii. Rapidly quenched lavas erupted close to vents are less oxidized than rapidly quenched lavas scooped from lava flows several kilometers away from the vents. These results demonstrate that sampling is of critical importance in determining the oxidation state of lava. The oxidation state of the vent lavas, below or at magnetite–wüstite (MW), is significantly lower than that previously reported for Hawaiian lavas (~FMQ). Similarly, rapidly quenched lavas from the ongoing Kilauea eruption and Loihi seamount, all have oxygen fugacities that are close to MW and on the low side of the range previously reported for Hawaiian lavas. From this we conclude that the initial oxygen fugacity of parental Hawaiian magmas is close to MW, not FMQ, and that previous estimates of the oxidation state of Hawaiian lavas may have been too high. This implies that the plume source of these magmas is also at or below MW, but not as reduced as the mantle source of mid-ocean ridge basalts. Additionally, Mauna Loa lavas appear to be slightly more reduced than Kilauea or Loihi lavas, perhaps indicating heterogeneous oxidation within the Hawaiian plume. [ABSTRACT FROM AUTHOR]

Two picrite flows from the SW rift zone of Mauna Loa contain xenoliths of dunite, harzburgite, lherzolite, plagioclase-bearing lherzolite and harzburgite, troctolite, gabbro, olivine gabbro, and gabbronorite. Textures and olivine compositions preclude a mantle source for the xenoliths, and rare earth element concentrations of xenoliths and clinopyroxene indicate that the xenolith source is not old oceanic crust, but rather a Hawaiian, tholeiitic-stage magma. Pyroxene compositions, phase assemblages and textural relationships in xenoliths indicate at least two different crystallization sequences. Calculations using the pMELTS algorithm show that the two sequences result from crystallization of primitive Mauna Loa magmas at 6 kbar and 2 kbar. Independent calculations of olivine Ni–Fo compositional variability in the plagioclase-bearing xenoliths over these crystallization sequences are consistent with observed olivine compositional variability. Two parents of similar bulk composition, but which vary in Ni content, are necessary to explain the olivine compositional variability in the dunite and plagioclase-free peridotitic xenoliths. Xenoliths probably crystallized in a small magma storage area beneath the rift zone, rather than the large sub-caldera magma reservoir. Primitive, picritic magmas are introduced to isolated rift zone storage areas during periods of high magma flux. Subsequent eruptions reoccupy these areas, and entrain and transport xenoliths to the surface. [ABSTRACT FROM PUBLISHER]