PYROCLASTIC ACTIVITY AND VENT STRUCTURES ON HAWAIIAN VOLCANOES Scott K. Rowland, University of Hawai‘i at Manoa -

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Presentation transcript:

PYROCLASTIC ACTIVITY AND VENT STRUCTURES ON HAWAIIAN VOLCANOES Scott K. Rowland, University of Hawai‘i at Manoa -

ERUPTION STYLES AND VENT FORMS

The intersection of a dike with the Earth’s surface: a curtain of “fire” (actually lava) 1971 eruption viewed from the Hawaiian Volcano Observatory, photo by Hawai‘i Volcanoes National Park staff

Expanding gas drives a lava fountain. The highest fountains in Hawai‘i are >500 m Technically, the base of the fountain is where the gas becomes 75% by volume, and this is usually 10s to 100s of meters below the vent rim.

Pu‘u ‘O‘o scoria cone (in the early 1990s) - -

Scoria cones on the lower south flank of Mauna Kea

~2 cm Typical high-fountaining pyroclasts: reticulite, scoria, Pele’s tears, and Pele’s hair

Crude layering in a typical high-fountaining deposit

Pele’s hair - produced in high fountains and skylights

Blanket of scoria downwind from Pu‘u ‘O‘o - -

Crude bedding and large bombs in a quarried scoria cone ~2 m

Cow dung bomb, Kilauea Iki (1959) pyroclastic deposit -

Large spindle bomb, East Maui Volcano, SW rift zone

low fountaining, spatter cones, and spatter ramparts (from Volcanoes in the Sea)

Spatter is fluid when it lands ~20 cm

~2 m-wide spatter cone, flank of Pu‘u ‘O‘o scoria cone behind - -

photo by P. Mouginis-Mark A line of spatter cones forms a spatter rampart

photo by P. Mouginis-Mark Satellitic shields, from eruptions with ~no pyroclastic activity

Mauna Iki satellitic shield, Kilauea SW rift zone -

- Kupaianaha lava pond and shield, with Pu‘u ‘O‘o scoria cone in the background - -

Kupaianaha lava pond, Kilauea ( ) - - ~20 m

(Kapoho, 1960) HYDROMAGMATIC ERUPTIONS

May 1924 phreatic eruption, Halema‘uma‘u view from Volcano House hotel, photo by Tai Sing Loo

Koko Rift rejuvenation-stage volcanism, Ko‘olau volcano, O‘ahu: -most of these eruptions occurred off the shoreline at the time -tuff cones, many nested and/or coalesced, resulted

from Volcanoes in the Sea (Macdonald et al. 1983) Molokini Islet, post-shield alkalic series, E. Maui Volcano

“surge” deposits, from lateral, turbulent deposition

Accretionary lapilli: liquid water in the eruption cloud

If you find footprints, do not do this ! They are fragile.

Keanakako‘i hydromagmatic ash, SW of Kilauea caldera lava

Keanakako‘i hydromagmatic ash, SW of Kilauea caldera - -

photo by P. Mouginis-Mark Keanakako‘i tephra exposed in upper SW rift zone fractures -

PAU