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-
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
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