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The role of magma-flux on eruptive behaviour during the formation of the monogenetic Ubehebe volcanic centre, Death Valley, California.

Rachael J. M. Baxter1, James D. L. White1, Judy Fierstein2, Greg Valentine3, Javiera Ruz Ginouves1, Caroline Bélanger1

  • Affiliations:  1 Department of Geology, University of Otago, Dunedin, New Zealand; 2 Volcano Science Center, U.S. Geological Survey, Moffett Field, California, USA; 3 Department of Geology, University at Buffalo, Buffalo, New York, USA. 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 15

  • Programme No: 3.7.22

  • Theme 3 > Session 7

Abstract

Phreatomagmatic eruption styles are often attributed to the presence or absence of water, but we propose that magma delivery rates play a greater role in controlling eruptive styles and fragmentation depths. Low magma flux or magma withdrawal favours subsurface phreatomagmatic explosions and cratering, while higher fluxes feed fountains and high plumes with widespread fallout. The Ubehebe crater cluster in Death Valley, USA, showcases how changes in magma supply shaped the weeks-to-months-long eruption from at least 14 vents ~ 2.1 ka. The eruption began with spattering and sporadic weak explosions along a N-S vent chain, ejecting large composite bombs (up to 2 m) along trend. As magma flux decreased, phreatomagmatic cratering formed the southern Amphitheatre Crater and emplaced surge deposits to the north. Renewed magma supply focused to the north, draining magma from the southern fissure and initiating phreatomagmatic explosions that extended the Amphitheatre northward, before driving violent strombolian activity that constructed a scoria cone and deposited fall material over ~93 km². Subsequent magma withdrawal renewed excavation of the Northern Amphitheater crater, truncating the scoria cone. Briefly increased magma supply then fed fire fountaining that formed the Little Hebe spatter cone. Later, E-W aligned craters formed orthogonally to the Amphitheatre craters. Overlapping deposits from these craters were capped by a ~9 km² fall deposit from Crater P, before formation of the Ubehebe Crater maar, the final and largest crater, as magma continued to withdraw.  This study highlights how magma delivery, rather than surficial hydrological changes, governs eruption progression and magma-water interactions.