Frequently asked questions
Why are eruptions in the submarine environment still poorly understood?
Primarily because there have been no direct observations of submarine lava emplacement, and only limited observations near shore where lava is entering the sea from subaerial eruptions. Our inferences, therefore, have to be made from observations and samples of older, inactive flows and vents. Similarly, the composition of magmas in the mantle or magma chambers have never been directly observed.
A submarine volcanic eruption has finally been witnessed. Scientists using the ROV Ropos to study the subduction-arc volcanoes of the Northern Mariana Islands in April 2004 dove into "Brimstone Pit", where they were engulfed in billowing, sulfurous smoke. They returned to the area in spring 2006 and witnessed red-hot rock erupting.
Why do submarine lava samples offer advantages over samples from land?
Because molten lava chills rapidly underwater, trapping gases and preventing further crystallization, and because the rocks are not exposed to acidic rain and rapid weathering as they are on land. The outer glassy rinds retain the composition of the melt and interior crystals often remain in good condition, so we can tell eruption temperatures and depth, differentiation due to storage in magma chambers, which volcano produced the flow, what evolutionary stage the volcano was in at the time, and possibly the age of the flow.
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Pillow lava rind from the Juan de Fuca Ridge, a spreading center off the northwestern US. The surface is glassy (black and shiny in the rock above) because it chilled quickly against the cold seawater and crystals had no time to form. The interior is crystalline (dull in the rock above) because it cooled more slowly. The ruler is one foot long. |
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Photomicrograph showing the glass rind from a lava pillow. This slice of rock is about 4 cm (~1.5 inches) long. The volcanic glass is the root beer colored layer above the dark, crystalline interior. It is transparent and pale brown when seen under a microscope. The white dots are vesicles left by gas bubbles in the lava. The very top dark layer is manganese oxide, which is precipitated from seawater over time, and just inside that layer is orange palagonite, produced from alteration of the volcanic glass. |
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Photomicrograph showing the crystalline interior of a lava flow. The tiny white lines are plagioclase feldspar crystals less than 1 mm long. |
Some on-line resources on plate tectonics, volcanoes, and earthquakes
- Information and tutorials on plate tectonics
- Glossary of volcanic and geologic terms (Volcano World)
- Submarine Volcanoes (Volcano World)
- Volcanoes for Kids (Volcano World)
- Smithsonian Global Volcanism Program
- USGS Hawaii Volcano Observatory
- USGS Earthquake Hazards Program
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Questions? Comments? Please contact Jenny Paduan