PYROCLASTIC ACTIVITY AND VENT STRUCTURES ON HAWAIIAN VOLCANOES Scott K. Rowland, University of...
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Transcript of PYROCLASTIC ACTIVITY AND VENT STRUCTURES ON HAWAIIAN VOLCANOES Scott K. Rowland, University of...
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PYROCLASTIC ACTIVITY AND VENT STRUCTURES ON HAWAIIAN VOLCANOES
Scott K. Rowland, University of Hawai‘i at Manoa-
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ERUPTION STYLES ANDVENT FORMS
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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
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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.
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Pu‘u ‘O‘o scoria cone (in the early 1990s)--
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Scoria cones on the lower south flank of Mauna Kea
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~2 cm
Typical high-fountaining pyroclasts: reticulite, scoria, Pele’s tears, and Pele’s hair
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Crude layeringin a typicalhigh-fountainingdeposit
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Pele’s hair - produced in high fountains and skylights
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Blanket of scoria downwind from Pu‘u ‘O‘o--
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Crude bedding and large bombs in a quarried scoria cone
~2 m
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Cow dung bomb, Kilauea Iki (1959) pyroclastic deposit-
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Large spindle bomb,East Maui Volcano,SW rift zone
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low fountaining, spatter cones, and spatter ramparts
(from Volcanoes in the Sea)
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Spatter is fluid when it lands
~20 cm
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~2 m-wide spatter cone, flank of Pu‘u ‘O‘o scoria cone behind--
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photo by P. Mouginis-Mark
A line of spatter cones forms a spatter rampart
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photo by P. Mouginis-Mark
Satellitic shields, from eruptions with ~no pyroclastic activity
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Mauna Iki satellitic shield, Kilauea SW rift zone-
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-Kupaianaha lava pond and shield, with Pu‘u ‘O‘o scoria conein the background
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Kupaianaha lava pond, Kilauea (1986-1992)- -
~20 m
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(Kapoho, 1960)
HYDROMAGMATIC ERUPTIONS
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May 1924 phreatic eruption, Halema‘uma‘u
view from Volcano House hotel, photo by Tai Sing Loo
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Eruption of Capelinhos, Azores, 1957. Note the “base surges” spreadinglaterally from thebase of the column.
http://volcanology.geol.ucsb.edu/surgecap.gif
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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
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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
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from Volcanoes in the Sea (Macdonald et al. 1983)
Molokini Islet, post-shield alkalic series, E. Maui Volcano
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“surge” deposits, from lateral, turbulent deposition
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Accretionary lapilli: liquid water in the eruption cloud
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If you find footprints, do not do this ! They are fragile.
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Keanakako‘i hydromagmatic ash, SW of Kilauea caldera--
1971 lava
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Keanakako‘i hydromagmatic ash, SW of Kilauea caldera--
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photo by P. Mouginis-Mark
Keanakako‘i tephra exposed in upper SW rift zone fractures-
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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
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PAU