Frequently asked questions
How might submarine volcanoes impact us, even though they are underwater?
The goal of our project is to better understand volcanic processes under different physical conditions, to gain insight into potentially destructive eruptions on land or in shallow water.
|Explosive eruptions: Explosive
fragmentation of lava to ash is a great hazard of volcanic eruptions on
land. Eruption under tremendous pressure of the deep sea limits gas
expansion and should limit lava fragmentation; yet we have found the
fragments there. Studying explosive eruptions under these confining
conditions may help us understand the processes closer to home.
Explosive eruptions in the deep sea are probably driven by magma that
is more gas-rich than previously recognized, and if so, could be an
additional source of gases that would add to the CO2 flux in the deep sea and affect pH near the eruption.
Read about explosive eruptions at Hot spot: Explosive eruptions and Flexural Arch, Mid-ocean ridges: Explosive eruptions, and Seamounts: Continental Margin Seamounts.
|Close to shore: Eruptions
offshore Hawaii, at Lo'ihi Seamount or other cones, are close enough to
shore that earthquakes would be felt, ejecta would cause turbidity in the water column, and the eruptions might even breach the surface. The seamounts off California are fairly
close to shore as well.
Read about Lo'ihi at Hot spot: Magmatic processes, Hydrothermal activity and Explosive eruptions, and the CA seamounts at Seamounts: Continental Margin Seamounts.
|Landslides trigger tsunamis: Enormous
landslides have occurred off all of the Hawaiian Islands and other
oceanic islands. On Oahu, half a volcano collapsed and the debris of
the Nuuanu Slide stretches for hundreds of kilometers. The tsunamis
generated by these slides would be devastating.
Read about landslides at Hot spot: Landslides, and evidence for large tsunami at Hot spot: Coral reefs.
|Extensive lava fields: Lava fields of the northeast and southwest flexural arches
off Hawaii are enormous in extent and eruption volume. The heat released during these eruptions would alter ocean circulation patterns and perhaps climate. We
don't know their distribution, how often they erupt, or what triggers them. We expect such immense eruptions to occur
Read about these flows at Hot spot: Flexural arch.
|Global climate change: Terraces off the Hawaiian Islands are ancient coral reefs
that drowned when sea level rose and the islands subsided. They record
glacial cycles from 15,000 (the shallowest reef off the Big Island) to
several million years ago (reefs off Oahu). They can help us understand
better the timing of glacial cycles and the changes to oceanic
conditions as climate changed.
Read about the reefs at Hot spot: Coral reefs.
|CA seamounts just dormant? Large volcanic seamounts (underwater mountains) occur off
the entire California coast. They represent a newly-recognized style of
volcanism: episodic magma emplacement through existing weak zones in
the crust. We have learned that they erupted sporadically over millions
of years, sometimes explosively. Even though they are not active at the
moment, we can't rule out future eruptions.
Read about these volcanoes at Seamounts: Continental Margin Seamounts .
|Release of methane: Slumping of unstable slopes may release significant
amounts of methane gas-hydrate, which would float upwards, decompose to
methane (a greenhouse gas), and be transferred to the atmosphere.
Read about slumps releasing methane in Margins: Gas hydrates and cold seeps.
Why are eruptions in the submarine environment still poorly understood?
Direct observations of submarine lava emplacement, until recently, were limited to observations near shore where lava entered the sea from subaerial eruptions. The composition of magmas in the mantle or magma chambers have never been directly observed. Our inferences, therefore, are predominantly made from observations and samples of older, inactive flows and vents.
Submarine volcanic eruptions now have 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, the first such observation. In May 2009 an expedition to the back-arc spreading center in the Lau Basin observed and mapped the West Mata eruption, the first deep-sea eruption ever seen.
- Lau Basin cruise log
- NOAA Explorations story 2006
- NOAA Explorations story 2004
- USGS newsletter story
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. From them 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.
||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.|
||Photomicrograph showing the glass rind from a lava pillow. This slice of rock is about 4 cm (~1.5 inches) long, seen under a microscope. The volcanic glass is the root beer colored layer above the dark, crystalline interior. 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, from alteration of the volcanic glass.|
||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 (under "Fun Stuff" at Volcano World)
and search online for "volcano lesson plans" or "volcano crafts" for many more
- Smithsonian Global Volcanism Program
- USGS Hawaii Volcano Observatory
- USGS Earthquake Hazards Program