Page 34 - Fundamentals of Physical Volcanology

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VOLCANIC SYSTEMS 11

SHALLOW MARINE AND CRATER LAKE ERUPTIONS
More dramatic hydromagmatic eruptions can occur
during eruptions which occur through water, either
through shallow seawater or through lakes which
are found in the craters at the summits of some
volcanoes.
A classic example of hydromagmatic interac-
tion in a shallow marine environment occurred at
Surtsey off the south coast of Iceland between 1963
and 1965. Eruptive activity was first noticed on
November 14, 1963 when the top of the volcano
was about 10 m below the water surface. A black
eruption cloud was initially seen just rising above
Fig. 1.17 Basaltic pillow lavas on the northeast rim of Lo'ihi
the sea surface. The cloud gradually grew to a
volcano, a submarine volcano located south of the island of
Hawai’I. Area shown is about 10 × 14 m. (Photograph taken height of ∼65 m. By the next day Surtsey had grown
in 1980 by A. Malahoff, University of Hawai’I, courtesy of above sea level and was erupting fairly constantly.
U.S. Geological Survey.) Scientists observing the eruption noted two domin-
ant styles of eruption. If seawater could flow into an
erupting vent, intermittent explosions occurred at
the coast and spill lava into the ocean. How the lava intervals of a few seconds to a few minutes. These
enters the sea affects the nature of the interaction explosions produced dark clouds of ash and steam
which occurs. In some cases the lava oozes out into which rose rapidly upwards and outwards from the
the sea and is rapidly cooled without an explosion vent producing what are known as cock’s tail
occurring, but in other cases the interaction is plumes or tephra jets (Fig. 1.19). The plumes rose
explosive and the fragments produced as the lava is to heights of ∼500 m, with individual bombs reach-
torn apart in the explosion are thrown into the air ing heights of ∼900 m. During the larger explosions,
and deposited on the shoreline forming a littoral base surges were generated. These are a kind of
cone (Fig. 1.18). pyroclastic cloud consisting of ash and steam which

Fig. 1.18 Lava from Kilauea volcano,
Hawai’I, entering the sea through a
lava tube and being torn apart
explosively. Chilled pyroclasts are
deposited on the shoreline forming a
littoral cone. Photograph by Pete
Mouginis-Mark, University of Hawai’I.