2. Volcanoes


2. Why Do Volcanoes Erupt?

See also Articles from 2002–2007

Non-chronological links:

Earthquake Resources

Volcano Resources

Internal Earth Processes - 36 multimedia resources from Teachers' Domain Earth and Space Science multimedia resources (movies and interactives).

Website discussing the origin of hot spot vulcanism.

Plate tectonic, continental drift animations from UC Berkeley Museum of Paleontology

Subduction in a Nutshell

USGS Hazards Gateway - about earthquakes, floods, hurricanes, landslides, tsunamis, and volcanoes.

USGS Volcano site

Volcano Observatories


Articles from 2008–present

2021-06-14. [https://eos.org/research-spotlights/magma-pockets-lie-stacked-beneath-juan-de-fuca-ridge] - Magma Pockets Lie Stacked Beneath Juan de Fuca Ridge. Source: By Sarah Stanley, Eos/AGU. Excerpt: Off the coast of the U.S. Pacific Northwest, at the Juan de Fuca Ridge, two tectonic plates are spreading apart at a speed of 56 kilometers per 1 million years. As they spread, periodic eruptions of molten rock give rise to new oceanic crust. Seismic images captured by Carbotte et al. now provide new insights into the dynamics of magma chambers that feed these eruptions. ...Sites of fast and intermediate spreading are typically fed by a thin, narrow reservoir of molten magma—the axial melt lens—that extends along the ridge at an intermediate depth in the oceanic crust, but still well above the mantle. ...some seafloor spreading sites around the world contain additional magma chambers beneath the axial melt lens. These additional chambers are stacked one above another in the “crystal mush zone,” an area of the actively forming oceanic crust that contains a low ratio of melted rock to crystallized rock. Beneath the Axial Seamount portion of the Juan de Fuca Ridge ...a 2020 investigation showed evidence of stacked magma chambers in the crystal mush zone beneath the large magma reservoir that underlies this on-axis hot spot. ...These findings...suggest that these stacked chambers are short-lived and may arise during periods when the crystal mush zone undergoes compaction and magma is replenished from the mantle below. The chambers do not cool and crystallize in place, but instead are tapped and contribute magma to eruptions and other crust-building processes.... 

2021-05-14. [https://eos.org/articles/high-school-junior-builds-cheap-earthquake-warning-device] - High School Junior Builds Cheap Earthquake Warning Device. Source: By Jack Lee, Eos/AGU. Excerpt: A Southern California high school junior has developed a low-cost seismometer using parts that total less than $100—a fraction of the cost of a scientific-grade system. ...“It’s small and cheap and accessible,” said Vivien He, a student at Palos Verdes Peninsula High School in Rolling Hills Estates, Calif. In April, she presented her work at the 2021 Annual Meeting of the Seismological Society of America. ...When an earthquake occurs, it generates compressional (P) waves and shear (S) waves, which emanate from the epicenter through Earth. Sensors that detect P waves can provide a warning before slower—but more destructive—S waves arrive. “Even with just a few seconds of warning, we can provide a useful alert to people: that they can do something…to protect themselves,” said Angie Chung, a seismologist at the Berkeley Seismological Laboratory in Berkeley, Calif. For instance, someone could duck under a table for protection from falling objects.... 

2021-02-25. Fleets of radar satellites are measuring movements on Earth like never before. By Julia Rosen, Science Magazine. Excerpt: East Africa ...the geologically active region has also given birth to dozens of volcanoes. Few have been monitored for warnings of a potential eruption, and until recently, most were believed to be dormant. Then, Juliet Biggs decided to take a closer look—or rather, a farther look. Biggs, a geophysicist at the University of Bristol, uses a technique called interferometric synthetic aperture radar (InSAR) to detect tiny movements of Earth’s surface from space. In a series of studies, she and her co-authors analyzed satellite data on the East African volcanoes. According to their latest results, which were published last month, 14 have been imperceptibly growing or shrinking in the past 5 years—a clue that magma or water is moving underground and that the volcanoes are not completely asleep. ...After data showed that the Corbetti volcano, which abuts the fast-growing city of Hawassa, Ethiopia, is inflating steadily at a rate of 6.6 centimeters per year, Biggs’s Ethiopian colleagues included it in the country’s geological hazard monitoring network. ...Individual GPS stations can track surface movements of less than 1 millimeter, but InSAR can measure changes almost as subtle across a swath hundreds of kilometers wide. ...With InSAR, scientists are tracking how ice streams flow, how faults slip in earthquakes, and how the ground moves as fluids are pumped in or out.... [https://www.sciencemag.org/news/2021/02/fleets-radar-satellites-are-measuring-movements-earth-never] See also A technique to track Earth’s subtle movements with orbiting radars is heating up, by Meagan Cantwell, Science Magazine, Mar 5, 2021.

2020-10-15. What Controls Giant Subduction Earthquakes? By Patricia Waldron, Eos/AGU. Excerpt: Subduction zones with a low dipping angle and thick sediments can produce giant earthquakes; this finding lets researchers estimate worst-case scenarios for coastlines around the world. Giant earthquakes—those greater than magnitude 8.5—are rare. ...Two of the largest earthquakes (and subsequent tsunamis) ever observed occurred in the past 2 decades, the 2004 Sumatra earthquake and the 2011 Tohoku earthquake. Both had an estimated magnitude of 9.1, which surprised scientists. “No one expected such large earthquakes at those places,” said Sobolev. Influential research dating back to 1980 proposed that earthquake magnitude depended on the age of the subducting plate and the rate of subduction. Specifically, a young oceanic plate with a rapid rate of subduction was estimated to produce the biggest earthquakes. But conditions at the Sumatran and Japanese subduction zones didn’t fit into this classical view. ...Now, a new study that models seismic activity in subduction zones has pinpointed the factors responsible for Earth’s largest earthquakes. ...Iskander Muldashev, a geophysical modeler at Bremen University, and Stephan Sobolev, a geodynamic modeler at GFZ Helmholtz Centre Potsdam, developed numerical models that simulate seismic cycles for subduction zones [paper]. The models showed that a shallow angle of subduction for the sinking oceanic plate and a thick layer of sediments in the trench where it meets the continental plate were the most important factors in creating a large rupture zone, leading to giant subduction earthquakes.... [https://eos.org/articles/what-controls-giant-subduction-earthquakes]  

2020-07-13. Desert quakes may have boosted chances of ‘big one’ striking California. By Roland Pease, Science Magazine. Excerpt: A pair of earthquakes that struck the remote California desert 1 year ago have raised the risk of “the big one” hitting Southern California, according to a new study. The research finds that the 2019 Ridgecrest, California, quakes shifted underground stresses, making the San Andreas fault—the state’s longest and most dangerous fault—three times more likely to rupture.... [https://www.sciencemag.org/news/2020/07/desert-quakes-may-have-boosted-chances-big-one-striking-california]  

2020-05-18. A Plate Boundary Emerges Between India and Australia. By Katherine Kornei, Eos/AGU. Excerpt: Tectonic plates blanket the Earth like a patchwork quilt. Now, researchers think they’ve found a new plate boundary—a line of stitching in that tectonic quilt—in the northern Indian Ocean. This discovery, made using bathymetric and seismic data, supports the hypothesis that the India-Australia-Capricorn plate is breaking apart, the team suggests. ...In 2012, two enormous earthquakes occurred near Indonesia. But these massive temblors—magnitudes 8.6 and 8.2—weren’t associated with the region’s notorious Andaman-Sumatra subduction zone. Instead, they struck within the India-Australia-Capricorn plate, which made them unusual because most earthquakes occur at plate boundaries. These earthquakes “reactivated the debate” about the India-Australia-Capricorn plate, said Aurélie Coudurier-Curveur, a geoscientist at the Institute of Earth Physics of Paris. Some scientists have proposed that this plate, which underlies most of the Indian Ocean, is breaking apart. That’s not a wholly unexpected phenomenon because this plate is being tugged in multiple directions, said Coudurier-Curveur.... [https://eos.org/articles/a-plate-boundary-emerges-between-india-and-australia] . 

2020-05-18. Mount St. Helens 40 years later: what we’ve learned, and still don’t know. By Warren Cornwall, Science Magazine. Excerpt: Charlie Crisafulli first visited Mount St. Helens 2 months after the 18 May 1980 eruption that ripped the top off the volcano, obliterated 600 square kilometers of forests, killed 57 people, and coated much of the Pacific Northwest in ash. He was a 22-year-old with an undergraduate degree in ecology.... Since then, Crisafulli—now an ecologist at the U.S. Forest Service’s Pacific Northwest Research Station—has spent much of each summer taking the mountain’s pulse as life returns. He recently spoke with ScienceInsider about the 40th anniversary of the eruption that has defined his scientific career, and shaped people’s understanding of how ecosystems respond to such devastation. ...Q: Are you still monitoring some of those same plots? A: There’s pieces of rebar that form the boundaries of plots I pounded in when I was 22 years old. I’m 62 now, and I’ve returned to those plots every year. And so for many of these things, there’s a tremendous amount of attachment to them. ...Q: What are some of the key scientific insights from the work? A: The initial impression was that nothing could have survived this level of disturbance and that the regeneration of the area’s ecology is going to come from the edges and from distant source populations. Instead what we found is that, in some 90% of the landscape, the rule was survivorship, albeit at greatly reduced numbers and in isolated refugias. ...What we’ve learned is that incredibly complex, early seral habitats [woodlands dominated by shrubs and grasses] developed that are food rich.... Even from space today, Mount St. Helens jumps out at you as this huge patch of something that’s different. What you’re looking down on is a landscape that supports a tremendous biomass of neotropical migrant birds, such as yellow warblers, orange-crowned warblers and willow flycatchers, and very diverse small mammal communities that are fundamentally different from adjacent old growth forests.... [https://www.sciencemag.org/news/2020/05/ecologist-has-been-studying-mount-st-helens-it-erupted-40-years-ago]  

2020-05-08. Are We Seeing a New Ocean Starting to Form in Africa? By Erik Klemetti, Eos/AGU. Excerpt: ...The entire Afar region in eastern Africa finds itself in the middle of changes that could split the continent, forming a new ocean basin. The magmatism at Erta Ale might be offering signs of this switch by mimicking the characteristics of a mid-ocean ridge. ... What we will be able to see standing on top of Erta Ale will change dramatically in 5 million, 50 million, or 100 million years. The question is whether Erta Ale and the Afar region will become a new ocean, or whether ongoing tectonic collisions to Africa’s north and east will prevent this transition from occurring.... [https://eos.org/articles/are-we-seeing-a-new-ocean-starting-to-form-in-africa

2020-01-06. Earthquake Strikes Puerto Rico, Toppling a Well-Known Natural Wonder. By Alejandra Rosa and Patricia Mazzei, The New York Times.

2019-12-26. Seismic Sensors in Orbit. By Timothy I. Melbourne, Diego Melgar, Brendan W. Crowell, and Walter M. Szeliga, Eos/AGU. 

2019-08-16. Sinking Wastewater Triggers Deeper, Stronger Earthquakes. By Mary Caperton Morton, Eos/AGU. 

2019-07-26. Sea of Galilee earthquakes triggered by excessive water pumping. By Michael Price, Science Magazine. 

2019-06-03. Déjà Vu: Understanding Subduction Zones’ Cycle of Seismicity. By Terri Cook, Eos/AGU. 

2019-01-25. Earth’s Devastating Power, Seen by Satellite. By Kimberly M. S. Cartier, Eos/AGU. 

2018-11-01. California’s new earthquake warnings deliver critical seconds of notice. By Paul Voosen, Science Magazine. 

2018-05-03. Vanuatu plans to permanently evacuate entire volcanic island. By Associated Press. 

2018-03-30. Are We Prepared for the Next Mega Eruption? By Fabio Florindo, AGU-Eos. 

2018-03-12. After a Volcano’s Ancient Supereruption, Humanity May Have Thrived. By Shannon Hall, The New York Times. 

2018-02-09. At Site of Japanese Volcano’s Supereruption, an Immense Lava Dome Lurks. By Nicholas S. Fleur, The New York Times. 

2017-12-27. Scientists Discover Stromboli-Like Eruption on Volcanic Moon. By JoAnna Wendel, Eos/AGU. 

2017-10-17. How to Trigger a Massive Earthquake. By Lucas Joel, Eos/AGU. 

2017-10-10. A Surprise From the Supervolcano Under Yellowstone. By Shannon Hall, The New York Times. 

2017-09-22. Scientists Closing in on the Dawn of Plate Tectonics. By Shannon Hall, Scientific American. 

2017-06-29. Homemade Lava Flows Fuse Science with Art on Video. By Lauren Lipuma and Derek Sollosi, Earth & Space Science News (EoS, AGU). 

2017-06-26. New Volcanic Island Unveils Explosive Past. By Shane J. Cronin, Marco Brenna, Ian E. M. Smith, Simon Barker, Manuela Tost, Murray Ford, Sisi Tonga’onevai, Taaniela Kula, and Rennie Vaiomounga, Earth & Space Science News (EoS, AGU

2017-06-22. “Fingerprinting” Volcanic Tremors May Help Forecast Eruptions. By Lucas Joel, for Earth & Space Science News, EoS, AGU. 

2017-04-13. What Led to the Largest Volcanic Eruption in Human History? By Sarah Witman, Earth & Space Science News (AGU). 

2016-01-04. Pinpointing the Trigger Behind Yellowstone’s Last Supereruption. By Aylin Woodward, EoS - Earth & Space Science News, AGU.

2016-11-18. Fracking can prime faults for subsequent quakes. By Ian Randall, Science.

2016-11-09. An Ancient Tsunami That Ended a Civilization Gets Another Look. By Henry Fountain, The New York Times.

2016-10-20. This volcano stopped an earthquake in its tracks, scientists say. By Ian Randall, Science.

2016-07-18. Spring tides trigger tremors deep on California’s San Andreas fault. By Eric Hand, Science.

2016-06-02. A New View of the Plate Dynamics Behind Earthquakes in Ecuador. By Sarah Stanley, EoS-Earth & Space Science News, AGU.

2016-05-17. Rumbling under the Volcanoes. By UC Berkeley Seismological Laboratory.

2016-05-16. Understanding Volcanic Eruptions Where Plates Meet. By Raffaele Azzaro and Rosanna De Rosa, EoS-Earth & Space Science News (AGU).

2016-04-26. Crowdsourced Seismology. By Elizabeth Deatrick, EoS Earth and Space Science News (AGU).

2016-01-15. Quake or Bomb? Seismic Waves Speak Truth, Even If Nations Don't. By Cody Sullivan, Earth & Space News (EoS; AGU).

2016-01-12. The 40,000-Mile Volcano. By William J. Broad, The New York Times.

2015-11-12. Better Forecasting for the Next Volcanic Eruption. By Valerio Acocella and Giovanni Chiodini. EoS Earth & Space Science News, AGU.

2015-08-24. How a Volcanic Eruption in 1815 Darkened the World but Colored the Arts. By William J. Broad, The New York Times.

2015-05-01. Nepal disaster presages a coming megaquake. By Eric Hand and Priyanka Pulla, Science.

2015-04-23. Two huge magma chambers spied beneath Yellowstone National Park. By Eric Hand, Science (AAAS).

2015-04-23. Oil and gas operations could trigger large earthquakes. By Eric Hand, Science (AAAS).

2015-03-23. No Need to Run in Hawaii: The Lava Is Coming, but Very Slowly. By Diane Cardwell, The New York Times.

2013-03-20.  Scientists Discover Layer of Liquified Molten Rock in Earth's Mantle | NSF Press Release 13-045. Relevant to GSS Energy Flow chapter 2. Excerpt: Scientists have discovered a layer of liquified molten rock in Earth's mantle that may be responsible for the sliding motions of the planet's massive tectonic plates. The finding may carry far-reaching implications, from understanding basic geologic functions of the planet to new insights into volcanism and earthquakes. ...The scientists discovered the magma layer at the Middle America trench off Nicaragua's shores. Using advanced seafloor electromagnetic imaging technology pioneered at SIO [Scripps Institution of Oceanography], the scientists imaged a 25-kilometer- (15.5-mile-) thick layer of partially melted mantle rock below the edge of the Cocos plate where it moves beneath Central America. ...For decades scientists have debated the forces that allow the planet's tectonic plates to slide across the Earth's mantle. ..."One of the longer-term implications of our results is that we are going to understand more about the plate boundary, which could lead to a better understanding of earthquakes," said Key. The researchers are now trying to find the source that supplies the magma in the newly discovered layer. See full article at http://www.nsf.gov/news/news_summ.jsp?cntn_id=127315&WT.mc_id=USNSF_51&WT.mc_ev=click.

2012 Oct 22. Italy Orders Jail Terms for 7 Who Didn't Warn of Deadly Earthquake. By Elisabetta Povoledo and Henry Fountain, The NY Times. Excerpt: ROME — Seven prominent Italian earthquake experts were convicted of manslaughter on Monday and sentenced to six years in prison for failing to give adequate warning to the residents of a seismically active area in the months preceding an earthquake that killed more than 300 people...The verdicts jolted the international scientific community, which feared they might open the way to an onslaught of legal actions against scientists who evaluate the risks of natural hazards….

2012 Feb 13.  Growth Spurt at a Bolivian Volcano Is Fertile Ground For Study.  By Jean Friedman-Rudovsky, The NY Times.  Excerpt:  …the 43-mile-long stretch of rocky soil is now an object of international scientific fascination. Satellite measurements show that the hill has been rising more than half an inch a year for almost 20 years, suggesting that the volcano, which last erupted more than 300,000 years ago, is steadily inflating….
…Taken together with other new research … the inflation means “we could be witnessing the development of a new supervolcano,” [said Oregon State University geologist Shanaka de Silva].
Such a volcano could produce an eruption of ash, rock and pumice 1,000 times the strength of the 1980 eruption of Mount St. Helens in Washington State, the worst volcanic event in modern American history, and 10,000 times that of the Icelandic eruptions in 2010 that paralyzed global air traffic for weeks.
Luckily, while the planet has 30 to 40 supervolcanoes — 10 of them potentially active — supereruptions occur only every 100,000 years or so….

2011 Dec. Insights from the great 2011 Japan earthquake.  By Thorne Lay and Hiroo Kanamori, Physics Today, page 33. On 11 March 2011, the nation of Japan and geophysicists around the world received a terrible surprise: A huge earthquake, significantly stronger than people had anticipated or prepared for in the region, struck off the northeastern shore of Honshu. Shear sliding on the fault where the Pacific Plate thrusts below Japan lasted for 150 anxiety-filled seconds, shifted the coast of Japan up to 5 m eastward, and lifted the sea floor by as much as 5 m over 15,000 km^2, an area comparable to the state of Connecticut. Displacements as large as 60 to 80 m—the largest ever measured for an earthquake—occurred near the subduction trench, and a total strain energy equivalent to a 100-megaton explosion was released during the sliding. This was the great 2011 Tohoku-oki earthquake, so-named for the region it struck. …The sudden sea-floor displacement generated a massive tsunami that swept onto hundreds of kilometers of coastline along the islands of Honshu and Hokkaidō. Tsunami waves 3–15 m high overtopped harbor-protecting tsunami walls and coastal margins and penetrated as far as 10 km inland along the coastal plain. The flood destroyed many small towns and villages, killed some 20,000 people, and initially displaced nearly half a million; six months later, tens of thousands were still living in high school gymnasiums and other temporary quarters (see PHYSICS TODAY, November 2011, page 20). …Researchers estimate its moment magnitude Mw at 9.0….

2011 Dec 5.  NASA RELEASE 11-405: NASA Finds 'Merging Tsunami' Doubled Japan Destruction.  Excerpt:  NASA and Ohio State University researchers have discovered the major tsunami generated by the March 2011 Tohoku-Oki quake centered off northeastern Japan was a long-hypothesized "merging tsunami."...
Data from NASA and European radar satellites captured at least two wave fronts that day. The fronts merged to form a single, double-high wave far out at sea. This wave was capable of traveling long distances without losing power. Ocean ridges and undersea mountain chains pushed the waves together along certain directions from the tsunami's origin.
The discovery helps explain how tsunamis can cross ocean basins to cause massive destruction at some locations while leaving others unscathed. The data raise hope that scientists may be able to improve tsunami forecasts….

2011 June 17.  From Devastation in Japan, Vital Data.  By Sindya N. Bhanoo, The NY Times. Excerpt: The earthquake in Japan earlier this year was massive and devastating, but it also provided researchers with an unprecedented amount of data, thanks to Japanese investment in earthquake-monitoring technology.
Writing in the journal Nature, Japanese scientists from the Geospatial Information Authority of Japan used the data to determine that the earthquake’s slip was unusually large in comparison with its rupture area, estimated to be 150,000 by 400,000 yards….

2011 March 12. Quake Moves Japan Closer to the U.S. and Alters Earth's Spin. By Kenneth Chang, The NY Times. Excerpt: The magnitude-8.9 earthquake that struck northern Japan on Friday not only violently shook the ground and generated a devastating tsunami, it also moved the coastline and changed the balance of the planet.
Global positioning stations closest to the epicenter jumped eastward by up to 13 feet.
...Meanwhile, NASA scientists calculated that the redistribution of mass by the earthquake might have shortened the day by a couple of millionths of a second and tilted the Earth’s axis slightly...

2010 October 18.  In Studying Haiti, a New Angle on an Earthquake's Intensity.  By Henry Fountain, The New York Times. Excerpt: ...A new study finds that in addition to the underlying geology, the geometry of local surface features contributed to the earthquake’s intensity as well. Susan E. Hough, a seismologist with the United States Geological Survey, and her colleagues found evidence that the shaking was amplified along a narrow ridge of hard rock south of the central city. The ridge was home to a popular hotel and other relatively well-built structures that were destroyed...

2010 June 23. NASA RADAR IMAGES SHOW HOW MEXICO QUAKE DEFORMED EARTH. NASA News. NASA has released the first-ever airborne radar images of the deformation in Earth's surface caused by a major earthquake -- the magnitude 7.2 temblor that rocked Mexico's state of Baja California and parts of the American Southwest on April 4. The data reveal that in the area studied, the quake moved the Calexico, Calif., region in a downward and southerly direction up to 80 centimeters (31 inches). The maps can be seen here.

2010 June 16. Volcanic Eruptions in North America Were More Explosive in Ancient Past. By Cheryl Dybas, National Science Foundation. Excerpt: …The researchers found the remains--deposited in layers of rocks--of eruptions of volcanoes located on North America's northern high plains that spewed massive amounts of sulfate aerosols into the atmosphere 40 million years ago. The scientists conducted their research at Scotts Bluff National Monument, Neb., and in surrounding areas.
…Volcanic eruptions may have significant impacts on the environment, Bao says, citing the 1991 Mt. Pinatubo and more recent Iceland volcanic eruptions.
…In the Nature paper, he and colleagues show that past sulfate aerosol formed in a different way than it does today, indicating a change from atmospheric conditions then to now.
…A similar volcanic event to the long-ago past likely will happen again, Bao says: in the next Yellowstone eruption.
…The closest analog, Bao believes, is the 1783 Laki, Iceland, eruption and the subsequent "dry fogs" in continental Europe.
…That event devastated Iceland's cattle population. People with lung problems suffered the worst, he says.
…In North America, the very next year's winter, that of 1784, was the longest and one of the coldest on record. The Mississippi River froze as far south as New Orleans. The French Revolution in 1789 may have been triggered by the poverty and famine caused by the eruption, scientists believe.

2010 April 29. Quake analysis rewrites history books. By Richard A. Lovett, Nature. Excerpt: A series of earthquakes that hit the North American heartland nearly 200 years ago were considerably smaller than reported in the history books, according to research presented at a meeting this week.
The quakes struck the New Madrid fault zone 200 kilometres south of St Louis, Missouri, in 1811 and 1812, long before modern seismometers allowed accurate measurements of their intensity. In the 1980s, however, some scientists estimated that the magnitudes of these quakes were over 8.0, says Susan Hough, a seismologist at the US Geological Survey's Pasadena office in California.
...To determine the most likely magnitude of the earthquake, Hough assembled historic accounts of the shaking, and asked experts in Canada, Italy, the United States and India to estimate the magnitude of the earthquake that produced them. "There were 300, maybe 400 accounts that had to be gone through carefully," she says.
..."The older the account and the more fragmentary, the easier it is to exaggerate," she says. "You have an account that says people were frightened and ran outside and chimneys came down. It's all breathless, but the bottom line may be that it was just a couple of chimneys."
Her experts fairly consistently estimated the magnitude of the New Madrid temblors at about 7.0....
...Still, a magnitude-7 earthquake isn't to be sneered at. "Haiti was a magnitude 7, and it's clear what that did in a region that wasn't prepared," says Hough....

2010 Mar 23. Quake-Catcher Network - Laptop Computers as Earth Quake Detectors.

2009 December 23, 2009. Sun, moon tug at San Andreas fault. John Wildermuth, SF Chronicle. Excerpt: Parts of the San Andreas fault are so sensitive to stress that the faint gravitational tug of the sun and the moon may be enough to cause tiny tremors 15 miles underground, a team of UC Berkeley seismologists has found. Water under extremely high pressure apparently acts as a lubricant for the rock, allowing even the smallest stresses to cause a measurable slippage. "For the first time we're getting a picture of what's going on beneath where earthquakes are happening," said Robert Nadeau of the Berkeley Seismological Laboratory, one of the authors of a report appearing Thursday in the journal Nature.
"... Unlike earthquakes, which can be large and generally short-lived jolts, the non-volcanic tremors deep underground may last for many tens of minutes at the level of a magnitude one earthquake, making them detectable only with sensitive instruments.
...Using years of readings from Parkfield and other sites, Nadeau, along with Roland Bürgmann, a UC Berkeley professor of earth and planetary science, and Amanda Thomas, a UC Berkeley graduate student, found that tremor activity varied with the effects of the sun, the moon and the ocean tides, which are driven by the moon.
...Since the strongest effects were seen when the pull of the moon and the sun was aligned with the direction of the fault's break (Los Angeles toward San Francisco in the case of the San Andreas Fault), the researchers reasoned that water trapped deep underground was the likely explanation for the tremors, lubricating the rock to make it move easier. The tremors so far have only been found in a relatively small number of fault zones, suggesting that underground water isn't found everywhere.

2009 April 13. Earthquakes’ Many Mysteries Stymie Efforts to Predict Them. By Kenneth Chang, The NY Times. Excerpt: Almost all earthquakes are small. A small segment of a fault, miles underground, jerks a little, the rumble imperceptible at the surface. But with a few quakes, the fault continues breaking, the ground jumps several feet and the world shakes in cataclysm.
“How does a rupture go from an inch a year to 3,000 miles per hour in a few seconds?” asked Ross S. Stein, a geophysicist at the United States Geological Survey.
No one knows.
This gap in knowledge makes earthquake prediction a frustrating and chancy exercise, and complicates the effort to calculate the risk that a human construction like a water reservoir or a geothermal power plant could inadvertently set off a deadly quake.
Last month, Giampaolo Giuliani, a technician who works on a neutrino experiment at the Gran Sasso National Laboratory in Italy, issued an urgent warning that a large earthquake was about to strike the Abruzzo region. The prediction was based on measurements he had made of high levels of radon gas, presumably released from rocks that were being ground up by the stresses of an incipient quake.
On April 6, a magnitude 6.3 earthquake hit L’Aquila in central Italy, killing almost 300 people. Mr. Giuliani claimed vindication for his prediction, which had been discounted by officials.
But earthquake experts like Dr. Stein are skeptical. Scientists studied radon as a possible earthquake warning signal as far back as the 1970s, and while they found convincing cases of radon releases before some earthquakes, ...the correlations were not strong enough or clear enough for useful predictions.
...“You can’t hang your hat on it unless it’s a reliable precursor and it happens before most earthquakes and it doesn’t happen at other times,” said Susan Hough, a seismologist at the geological survey.
To complicate matters, Mr. Giuliani’s prediction was off in time and place. He had predicted that the quake would hit a week earlier in a town 30 miles away....

2009 March 19. Underwater volcano erupts off Tongan coast. The Guardian. Video: Smoke fills the sky as an undersea volcano erupts off the coast of Ha'apai in Tonga.

2009 January 16. Heads Up for Earthquakes. ScienceMatters@Berkeley, Volume 6, Issue 40. Excerpt: ...Unlike hurricanes or volcanic eruptions, earthquakes can't be forecast days or weeks in advance. The next best solution, says seismologist Richard Allen, is an earthquake early warning system. "If there was an earthquake now, we'd want to know how much it's going to shake here, and how much time we have," says Allen, a Berkeley professor of earth and planetary sciences.
Allen is in the process of implementing an earthquake early warning system in temblor-prone California. Called ElarmS, the system is designed to detect the imminent arrival of a strong earthquake and then warn a vulnerable public.
...the ElarmS system operates much like a spider's silken web. An existing network of seismographs around the state continuously transmits earth movements to several central processing hubs. Just as a spider uses vibrations to judge the size and location of trapped insects, modeling programs at the centers use this ground shaking data to calculate how serious any tremor is likely to be. If the quake looks to be a whopper, the models will generate a map of the most serious shaking areas. Civil safety systems can then alert the public to the danger.
...As is, ElarmS has already proved its mettle. On October 30, 2007, just 20 days after ElarmS went online for testing in Northern California, the magnitude 5.4 Alum Rock earthquake rippled across urban San Jose. ElarmS accurately estimated the magnitude and the extent of ground shaking for San Francisco two seconds before the temblor reached city limits. Being in test mode slowed the system's responses. If ElarmS had been running normally, the warning time would have been closer to ten seconds-long enough for most people to reach safer ground....

2008 January 17. NASA Tsunami Research Makes Waves in Science Community. Excerpt: PASADENA, Calif. - A wave of new NASA research on tsunamis has yielded an innovative method to improve existing tsunami warning systems, and a potentially roundbreaking new theory on the source of the December 2004 Indian Ocean tsunami. In one study, published last fall in Geophysical Research Letters, researcher Y. Tony Song of NASA's Jet Propulsion Laboratory, Pasadena, Calif., demonstrated that real-time data from NASA's network of global positioning system (GPS) stations can detect ground motions preceding tsunamis and reliably estimate a tsunami's destructive potential within minutes, well before it reaches coastal areas. The method could lead to development of more reliable global tsunami warning systems, saving lives and reducing false alarms. ..."Tsunamis can travel as fast as jet planes, so rapid assessment following quakes is vital to mitigate their hazard," said Ichiro Fukumori, a JPL oceanographer not involved in the study. "Song and his colleagues have demonstrated that GPS technology can help improve both the speed and accuracy of such analyses."
...Scientists have long believed tsunamis form from vertical deformation of seafloor during undersea earthquakes. However, seismograph and GPS data show such deformation from the 2004 Sumatra earthquake was too small to generate the powerful tsunami that ensued. Song's team found horizontal forces were responsible for two-thirds of the tsunami's height, as observed by three 

Alfred Wegener proposed the theory of continental drift - long before the idea was commonly accepted.