PYROCLASTIC ACTIVITY AND VENT STRUCTURES

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PYROCLASTIC ACTIVITY AND VENT STRUCTURES ON
HAWAIIAN VOLCANOES
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ERUPTION STYLES AND VENT FORMS
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The intersection of a dike with the Earths
surface a curtain of fire (actually lava)
1971 eruption viewed from the Hawaiian Volcano
Observatory, photo by Hawaii Volcanoes National
Park staff
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Expanding gas drives a lava fountain. The
highest fountains in Hawaii are gt500 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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Scoria cones on the lower south flank of Mauna Kea
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Typical high-fountaining pyroclasts reticulite,
scoria, Peles tears, and Peles hair
2 cm
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Crude layering in a typical high-fountaining depos
it
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Peles hair - produced in high fountains and
skylights
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Crude bedding and large bombs in a quarried
scoria cone
2 m
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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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A line of spatter cones forms a spatter rampart
photo by P. Mouginis-Mark
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Satellitic shields, from eruptions with no
pyroclastic activity
photo by P. Mouginis-Mark
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-
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20 m
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HYDROMAGMATIC ERUPTIONS
(Kapoho, 1960)
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May 1924 phreatic eruption, Halemaumau
view from Volcano House hotel, photo by Tai Sing
Loo
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Eruption of Capelinhos, Azores, 1957. Note the
base surges spreading laterally from the base
of the column.
http//volcanology.geol.ucsb.edu/surgecap.gif
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Eruption of Taal, Philippines, 1966. Note the
base surges spreading laterally from the base
of the column.
http//assets.nydailynews.com/img/2009/02/03/gal_v
olcano_1965_taal.jpg
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Koko Rift rejuvenation-stage volcanism, Koolau
volcano, Oahu -most of these eruptions
occurred off the shoreline at the time -tuff
cones, many nested and/or coalesced, resulted
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Molokini Islet, post-shield alkalic series, E.
Maui Volcano
from Volcanoes in the Sea (Macdonald et al. 1983)
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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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1971 lava
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photo by P. Mouginis-Mark
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Did all this happen in a few hundred years? A
few years?
Diagram from McPhie et al. (1990)
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PAU