PYROCLASTIC ACTIVITY AND VENT STRUCTURES ON HAWAIIAN VOLCANOES

Scott K. Rowland, University of Hawai‘i at Manoa-

ERUPTION STYLES ANDVENT 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 layeringin a typicalhigh-fountainingdeposit

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 conein the background

--

Kupaianaha lava pond, Kilauea (1986-1992)- -

~20 m

(Kapoho, 1960)

HYDROMAGMATIC ERUPTIONS

May 1924 phreatic eruption, Halema‘uma‘u

view from Volcano House hotel, photo by Tai Sing Loo

Eruption of Capelinhos, Azores, 1957. Note the “base surges” spreadinglaterally from thebase of the column.

http://volcanology.geol.ucsb.edu/surgecap.gif

Eruption of Taal, Philippines, 1966. Note the “base surges” spreadinglaterally from thebase of the column.

http://assets.nydailynews.com/img/2009/02/03/gal_volcano_1965_taal.jpg

Koko Rift rejuvenation-stagevolcanism, 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--

1971 lava

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

photo by P. Mouginis-Mark

Keanakako‘i tephra exposed in upper SW rift zone fractures-

Diagram from McPhie et al. (1990)

Did all this happenin a few hundredyears? A few years?

Painting of Keoua’s warriors, killedby an explosive eruption.

-

~1500 AD

~1700 AD

~1790 AD

Age dates byDon Swanson,USGS HVO

PAU