Geology topics

Julia E. Hammer

Publications and source records attributed to Julia E. Hammer.

3 recordsLinked to original sources

USGS2025

Crustal to mantle melt storage during the evolution of Hawaiian volcanoes

As the Pacific Plate migrates over the mantle plume below Hawaiʻi, magma flux decreases, resulting in changes in eruptive volume, style, and composition. It is thought that melt storage becomes deeper and ephemeral with the transition from highly voluminous tholeiitic (shield stage) to the less voluminous alkaline (post-shield and rejuvenation stages) magmatism. To quantitatively test this, we applied high-precision fluid inclusion barometry via Raman spectroscopy to samples from representative volcanoes of different evolutionary stages. This suggests an evolution from shield-stage shallow magma storage (~1 to 2 kilometers) for Kīlauea to a post-shield stage that includes crustal magma storage within the volcanic edifice (~2 kilometers) and deeper storage below the Moho (~20 to 27 kilometers) for Haleakalā. The rejuvenation stage (Diamond Head) displays mantle-dominated storage (~22 to 30 kilometers). High melt fluxes likely form stable conduits from the mantle to a shallow reservoir in the shield volcanoes. As melt flux decreases, the Moho becomes the boundary controlling melt stagnation and evolution.

Hawaii↗

USGS2021

Evaluating lava flow propagation models with a case study from the 2018 eruption of Kīlauea Volcano, Hawai'i

The 2018 lower East Rift Zone (LERZ) eruption of Kīlauea, Hawai’i, provides an excellent natural laboratory with which to test models of lava flow propagation. During early stages of eruption crises, the most useful lava flow propagation equations utilize readily determined parameters and require fewer a priori assumptions about future behavior of the flow. Here, we leverage the numerous observations of lava flows collected over the duration of the eruption crisis at Kīlauea in 2018 to test simple lava flow propagation models. These models track the one-dimensional propagation of the flows according to three main rheological restraining forces: bulk viscosity, yield strength, and growth of a surface crust. We calculate the predicted changes in length through time of three flows that vary in bulk composition, crystal content, and total flow length. Cooler flows that are more crystal-rich tend to be more dominated by crust growth, though early stages of propagation can be controlled by bulk viscosity. We find that variations in effusion rate significantly impact flows that are short-lived; flows that are produced during steady-state effusion are readily approximated by average values for the entire flow. Thus, accurate knowledge of variations in effusion rate are critical to accurate lava flow propagation forecasting.

Hawaii↗

USGS2006

Submarine sliver in North Kona: A window into the early magmatic and growth history of Hualalai Volcano, Hawaii

Two manned submersible dives examined the Hualalai Northwest rift zone and an elongate ridge cresting at 3900 mbsl during a 2002 JAMSTEC cruise. The rift zone flank at dive site S690 (water depth 3412–2104 m) is draped by elongated and truncated pillow lavas. These olivine-rich tholeiitic lavas are compositionally indistinguishable from those examined further south along the bench, except that they span a wider range in dissolved sulfur content (200–1400 ppm). The elongate ridge investigated in dive S692, located at the base of the bench, is a package of distinct lithologic units containing volcaniclastic materials, glassy pillow breccias, and lava blocks; these units contain a range of compositions including tholeiitic basalt, transitional basalt, and hawaiite. The textures, compositions, and stratigraphic relationships of materials within the elongate ridge require that a variety of transport mechanisms juxtaposed materials from multiple eruptions into individual beds, compacted them into a coherent package of units, and brought the package to its present depth 10 km from the edge of the North Kona slump bench. Sulfur-rich hawaiite glasses at the base of the elongate ridge may represent the first extant representatives of juvenile alkalic volcanism at Hualalai. They are geochemically distinct from shield tholeiite and post-shield alkalic magmas, but may be related to transitional basalt by high-pressure crystal fractionation of clinopyroxene. Tholeiitic glasses that compose the majority of the exposed outcrop are similar to Mauna Kea tholeiites and other Hualalai tholeiites, but they differ from younger basalts in having greater incompatible element enrichments and higher CaO for a given MgO. These differences could arise from small extents of partial melting during the transition from alkalic to shield stage magmatism. Low sulfur contents of most of the volcaniclastic tholeiites point to early emergence of Hualalai above sea level relative to the development of the midslope slump bench.

Hawai'i↗