Geology topics

Richard W. Hazlett

Publications and source records attributed to Richard W. Hazlett.

6 recordsLinked to original sources

USGS2024

Tracking magma pathways and surface faulting in the Southwest Rift Zone and the Koaʻe fault system (Kīlauea volcano, Hawai ‘i) using photogrammetry and structural observations

Volcanic islands are often subject to flank instability, resulting from a combination of magmatic intrusions along rift zones and gravitational spreading causing extensional faulting at the surface. Here, we study the Koaʻe fault system (KFS), located south of the summit caldera of Kīlauea volcano in Hawaiʻi, one of the most active volcanoes on Earth, prone to active faulting, episodic dike intrusions, and flank instability. Two rift zones and the KFS are major structures controlling volcanic flank instability and magma propagation. Although several magmatic intrusions occurred over the KFS, the link between these faults, two nearby rift zones and the flank instability, is still poorly studied. To better characterize the KFS and its structural linkage with the surrounding fault and rift zones, we performed a detailed structural analysis of the extensional fault system, coupled with a helicopter photogrammetric survey, covering part of the south flank of Kīlauea. We generated a high-resolution DEM (~ 8 cm) and orthomosaic (~ 4 cm) to map the fracture field in detail. We also collected ~ 1000 ground structural measurements of extensional fractures during our three field missions (2019, 2022, and 2023). We observed many small, interconnected grabens, monoclines, rollover structures, and en-echelon fractures that were in part previously undocumented. We estimate the cumulative displacement rate across the KFS during the last 600 ~ 700 years and found a decrease toward the west of the horizontal component from 2 to 6 cm per year, consistent with GNSS data. Integrating morphology observations, fault mapping, and kinematic measurements, we propose a new kinematic model of the upper part of the Kīlauea’s south flank, suggesting a clockwise rotation and a translation of a triangular wedge. This wedge is bordered by the extensional structures (ERZ, SWRZ, and the KFS), largely influenced by gravitational spreading. These findings illustrate a structural linkage between the two rift zones and the KFS, the latter being episodically affected by dike intrusions.

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USGS2024

Origins and nature of large explosive eruptions in the lower East Rift Zone of Kīlauea volcano, Hawaii: Insights from ash characterization and geochemistry

Several powerful explosive eruptions have taken place in the populated lower East Rift Zone of Kīlauea within the past ∼750 years. These have created distinctive landforms, including a tephra rim enclosing Puʻulena Crater immediately south of the Puna Geothermal Venture power station, a tuff cone at Kapoho Crater near the eastern cape of the Island of Hawaiʻi, and a set of littoral cones, the Sand Hill in Nānāwale, where the 1840 lava flow poured into the ocean. Kapoho Crater tuff cone is the largest of these recent pyroclastic features. Mineral, glass, and melt inclusion analyses of tuff cone ash and later fissure-related scoriaceous materials also found within the crater indicate slightly evolved basaltic magmas (1120–1130 °C) that are compositionally similar to parts of the effusive lower East Rift Zone eruptions in 1955 and 2018. Tuff cone magmas were stored at depths of ∼2.5–3.5 km and had pre-eruptive volatile contents (0.5–0.8 wt% H 2 O, 280–340 ppm CO 2 , 1400–1800 ppm S) similar to other Kīlauea eruptions (e.g., 1959, 1960), suggesting that internal magma properties were unlikely to account for the unusual explosiveness of this eruption. Tephra componentry, grain-size analyses, and field observations confirm that the cone grew during a phreatomagmatic eruption mostly of vitric ash, probably where a fissure opened across the coastline or shallow ocean floor nearby. Supporting this hypothesis is the identification of at least two genera of marine diatoms within tuff cone strata. Sand Hill littoral cone ash is also vitric like that of Kapoho Crater, but distinctly coarser with abundant fluidal ejecta represented. In contrast, the Puʻulena Crater eruption deposited lithic ash and related blocks with minor juvenile magmatic contribution; a phreatomagmatic eruption that was dominantly phreatic. Differences in eruption styles are related to unique mechanics that tephra analyses help us interpret. While powerful explosive eruptions in the lower East Rift Zone are rare, they present a definite future hazard for inhabitants in this part of Hawaii.

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USGS2023

Chemistry and petrography of early 19th century basaltic andesites and basalts from the Kamakaiʻa Hills in the Southwest Rift Zone of Kīlauea volcano, Hawaiʻi

Kīlauea is a frequently active, open-system volcano on the Island of Hawaiʻi known for erupting olivine-dominated tholeiitic basalt compositions. On rare occasions it erupts more differentiated magmas (<1% of erupted volume), such as basaltic andesites and andesites, from its rift zones. These differentiated magmas offer an opportunity to understand better the petrology, magma storage, magma mixing, and eruptive triggers that occur in Kīlauea's rift zone reservoirs. This study focuses on an eruption from the Southwest Rift Zone of Kīlauea, which is dominantly basaltic andesite with subordinate basalt. This eruption originated at the Kamakaiʻa Hills during the early 19th century and has two eruptive phases: 1) an early ‘a‘ā phase that is primarily exposed in the eastern part of the flow field, with minor western lobes, and 2) a late pāhoehoe phase that makes up most of the western part of the flow field. The early ‘a‘ā phase covers at least 5.8 km 2 with an erupted volume of ∼150 × 10 6 m 3 and consists of uniform composition basaltic andesites with 3.72–4.15 wt% MgO over its ∼7 km flow length. The late pāhoehoe phase reached >10 km from its vent, covers an area of ∼7.1 km 2 , has a volume of ∼100 × 10 6 m 3 , and initially erupted basaltic andesite near its vent (4.50–5.64 wt% MgO extending to 3.8 km from vent) with channel and tube-fed basalt (6.21–12.38 wt% MgO sampled at >3.8 km from vent) emplaced during its waning stages. Most Kamakaiʻa Hills lavas are crystal-poor, containing ≤1.5% glomerocrysts and individual phenocrysts of plagioclase + clinopyroxene + Fe Ti oxides ± orthopyroxene, as well as olivine in lavas with >6 wt% MgO. Major-oxide and trace-element concentrations throughout the Kamakaiʻa Hills lavas demonstrate the involvement of three distinct magmatic processes. First, the basaltic andesites of the early ‘a‘ā phase are the products of fractionation of plagioclase + clinopyroxene + Fe Ti oxides ± orthopyroxene, indicative of magmas that have been stored in rift zone reservoirs for decades or longer. Second, the near-vent (within ∼400 m of vent) basaltic andesites of the late pāhoehoe phase yield chemical concentrations that indicate magma mixing with a more differentiated magma (of a similar evolved composition to basaltic andesites at ∼55–56 wt% SiO 2 and ∼3.4–4.1 wt% MgO that erupted in the lower East Rift Zone in 2018). Third, the progressively more mafic magma (containing olivine + plagioclase + clinopyroxene) that continued to erupt throughout the waning stages of activity suggests an eruptive triggering process whereby an intruding summit or uprift reservoir basalt overpressurized and forced out the stored, differentiated magma of the Kamakaiʻa Hills rift zone reservoir.

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USGS2021

Correcting the historical record for Kīlauea Volcano's 1832, 1868, and 1877 summit eruptions

Three fissure eruptions are known to have occurred along the northeastern edge of Kīlauea's summit caldera in the 19th century—in the years 1832, 1868, and 1877. Modern portrayal of these eruptions on maps and in written sources indicates that the 1832 eruption was from a fissure on the side of the Poliokeawe scarp south of Byron Ledge, the 1868 eruption was from a fissure on the southern wall of Kīlauea Iki Crater and fed a lava flow that covered the bottom of that crater, and the eruption in 1877 occurred on the floor of Keanakākoʻi Crater, as well as from a fissure of uncertain location on the east wall of the caldera below Byron Ledge. New geologic mapping and a review of historical documents and maps contradict these views. We find, instead, that: (1) the 1832 eruption discharged from a fissure on Byron Ledge (not Poliokeawe scarp), from another fissure on the southwestern wall of Kīlauea Iki Crater, and from at least one fissure along the east side of Kīlauea caldera below Byron Ledge; (2) the 1868 lava erupted through the floor of Kīlauea Iki Crater, not from a fissure in its southwestern wall; and (3) the 1877 lava erupted from Kīlauea Iki Crater's mid-wall fissure (until now believed to have opened in 1868), from the fissure previously assigned an 1832 date on Poliokeawe escarpment, and from a precisely relocated vent on the northeastern wall of the caldera. Finally, no conclusive first-hand accounts of the late 19th century eruption in Keanakākoʻi Crater were identified, leaving in doubt the often-inferred 1877 date for this event. Possible alternative dates include 1868, 1879, and 1881.

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USGS2019

Undocumented late 18th- to early 19th-century volcanic eruptions in the Southwest Rift Zone of Kīlauea Volcano, Hawai‘i

The historical record of volcanic activity at Kīlauea Volcano on the Island of Hawaiʻi begins with the phreatomagmatic blasts of 1790. Three decades later, in 1823, the first party of non-Hawaiian visitors, organized by the English Reverend William Ellis, reached Kīlauea’s summit. A detailed narrative by Ellis includes an account of an eruption in Kīlauea’s Southwest Rift Zone that occurred shortly before his visit. In the absence of other source materials, the interval between the eruptions of 1790 and 1823 has been overlooked by geologists working at Kīlauea, with the presumption that little if anything took place volcanically outside of the summit caldera during that time. Careful stratigraphic observations combined with radiocarbon dating demonstrate that during these years a set of Southwest Rift Zone eruptions took place, including two that were long-lasting (weeks to months). Inclusion of these events gives a more complete historical (post-1790) record for Kīlauea and a better understanding of its eruptive behavior.

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USGS1983

Thermal areas on Kilauea and Mauna Loa Volcanoes, Hawaii

Active thermal areas are concentrated in three areas on Mauna Loa and three areas on Kilauea. High-temperature fumaroles (115-362°C) on Mauna Loa are restricted to the summit caldera, whereas high-temperature fumaroles on Kilauea are found in the upper East Rift Zone (Mauna Ulu summit fumaroles, 562°C), middle East Rift Zone (1977 eruptive fissure fumaroles), and in the summit caldera. Solfataric activity that has continued for several decades occurs along border faults of Kilauea caldera and at Sulphur Cone on the southwest rift zone of Mauna Loa. Solfataras that are only a few years old occur along recently active eruptive fissures in the summit caldera and along the rift zones of Kilauea. Steam vents and hot-air cracks also occur at the edges of cooling lava ponds, on the summits of lava shields, along faults and graben fractures, and in diffuse patches that may reflect shallow magmatic intrusions.

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