Seismic survey at the Mariana trench will follow water dragged down into the Earth’s mantle

After the cruise some of the scientists set sail on a smaller boat to install seismometers on five islands surrounding the trench. The volcano that created one of these islands, Pagan, has erupted several times over the past 30 years. Fortunately it was only moderately active when the team was there, expelling steam that reflects the setting sun in this photo. -  Heather Relyea
After the cruise some of the scientists set sail on a smaller boat to install seismometers on five islands surrounding the trench. The volcano that created one of these islands, Pagan, has erupted several times over the past 30 years. Fortunately it was only moderately active when the team was there, expelling steam that reflects the setting sun in this photo. – Heather Relyea

Last month, Doug Wiens, PhD, professor of earth and planetary science at Washington University in St. Louis, and two WUSTL students were cruising the tropical waters of the western Pacific above the Mariana trench aboard the research vessel Thomas G. Thompson.

The trench is a subduction zone, where the ancient, cold and dense Pacific plate slides beneath the younger, lighter high-riding Mariana Plate, the leading edge of the Pacific Plate sinking deep into the Earth’s mantle as the plates slowly converge.

Taking turns with his shipmates, Wiens swung bright-yellow ocean bottom seismometers and hydrophones off the fantail, and lowered them gently to the water’s surface, as the ship laid out a matrix of instruments for a seismic survey on the trench.

The survey, which Wiens leads together with Daniel Lizarralde, PhD, of the Woods Hole Oceanographic Institution, will follow the water chemically bound to the down-diving Pacific Plate or trapped in deep faults that open in the plate as it bends. The work is funded by the National Science Foundation.

Scientists have only recently begun to study the subsurface water cycle, which promises to be as important as the more familiar surface water cycle to the character of the planet.

Hydration reactions along the subducting plate are thought to carry water deep into the Earth, and dehydration reactions at greater depths release fluids into the overlying mantle that promote melting and volcanism.

The water also plays a role in the strong earthquakes characteristic of subduction zones. Hydrated rock and water under high pressure are thought to lubricate the boundary between the plates and to permit sudden slippage.

Dropping the instruments

Between Jan. 26 and Feb. 9, working day and night, watch-on and watch-off, the Thompson laid down 80 ocean bottom seismometers and five hydrophones.

The hydrophones, which detect pressure waves and convert them into electrical signals, provide less information than the seismometers, which register ground motion, but they can be tethered four miles deep in the water column where the bottom is so far down seismometers would implode as they sank.

The Thompson sailed over some of the most famous real estate in the world, the Mariana trench, which includes the bathtub-shaped depression called the Challenger Deep, to which Avatar director James Cameron plans to plunge in a purpose-built one-man submersible called the Deep Challenger.

Seven miles down, the pressure in the Deep is 1,000 atmospheres (1,000 times the pressure at sea level on dry land) or roughly 8 tons per square inch. Seismometers, says Wiens, only go down four miles.

The trench is created by the subduction of some of the world’s oldest oceanic crust, which plunges underneath the Mariana Isalnds so steeply at places that it is going almost straight down.

The active survey

After the Thompson returned to Guam and Wiens flew back to St. Louis to resume his less romantic duties as chair of the Department of Earth and Planetary Sciences, the research vessel Marcus G. Langseth began to sail transects above the matrix of seismometers, firing the 36-airgun array on its back deck.

The sound blasts reflected from the boundaries between rock layers a few miles beneath the ocean floor were picked up by an five-mile-long “streamer,” or hose containing many hydrophones, towed just beneath the surface behind the ship.

This was the “active” stage of a seismic survey with a “passive” stage yet to come.

After the seismic survey, the Langseth returned to pick up 60 seismometers, leaving behind 20 broadband seismometers and the hydrophones that will listen for a year to the reverberations from distant earthquakes, allowing the seismologists to map structures as deep as 60 miles beneath the surface.

In the meantime Patrick Shore, a research scientist in earth and planetary science, and two Washington University students had set sail across the ocean in a tiny vessel, the Kaiyu III, to install seismometers on the Mariana islands that will also supply data for the “passive” stage of the survey.

Water, water everywhere

Water plays a completely different role at depth than it does on the surface of the Earth. Water infiltrating the mantle through faults hydrates the mantle rock on either side of the fault.

In a low temperature process called serpentinization, it transforms mantle rock such as the green periodotite into serpentinite, a rock with a dark scaly surface like a serpent’s skin.

As the slab plunges yet deeper, dehydration reactions release water, which at such great pressure and temperature exists as a supercritical fluid that can drift through materials like a gas and dissolve them like a fluid. The fluid rises into the overlying mantle where it lowers the melting point of rock and triggers the violent eruptions of magma that created the Mariana Islands, to which Shore was sailing.

“We think that much of the water that goes down at the Mariana trench actually comes back out of the earth into the atmosphere as water vapor when the volcanos erupt hundreds of miles away,” Wiens says.

The scientists will map the distribution of serpentinite in the subducting plate and overlying mantle, by looking for regions where certain seismicwaves travel more slowly than usual.

Tracing the water cycle within subduction zones will allow the scientists to better understand island-arc volcanism and subduction-zone earthquakes, which are among the most powerful in the world

But the role of subsurface water is not limited to these zones. Scientists don’t know how subduction got started in the first place, but water may be a necessary ingredient. Venus, which is in many ways similar to Earth, has volcanism but no plate tectonics, probably because it is bone dry.

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Seismologists have just returned from a cruise in the Western Pacific to lay the instruments for a seismic survey that will follow the water chemically bound to or trapped in the down-diving Pacific Plate at the Mariana trench, the deep trench to which Avatar director James Cameron is poised to plunge. This video combines an interview of co-PI Doug Wiens of Washington University in St. Louis and the videos he took on the cruise. – Doug Wiens/Clark Bowen/WUSTL

Scientists study earthquake triggers in Pacific Ocean

The CRISP research site is located 174 km (108 miles) off the coast of Costa Rica. -  Original is modified by IODP
The CRISP research site is located 174 km (108 miles) off the coast of Costa Rica. – Original is modified by IODP

New samples of rock and sediment from the depths of the eastern Pacific Ocean may help explain the cause of large, destructive earthquakes similar to the Tohoku Earthquake that struck Japan in mid-March.

Nearly 1500 meters (almost one mile) of core collected from the ocean floor near the coast of Costa Rica reveal detailed records of approximately 2 million years of tectonic activity along a seismic plate boundary.

The samples were retrieved with the scientific drilling vessel JOIDES Resolution during the recent month-long Integrated Ocean Drilling Program (IODP) Costa Rica Seismogenesis Project (CRISP) Expedition. Participating scientists aim to use the samples better understand the processes that control the triggering of large earthquakes at subduction zones, where one plate slides beneath another.

“We know that there are different factors that contribute to seismic activity – these include rock type and composition, temperature differences, and how water moves within the Earth’s crust,” explained co-chief scientist Paola Vannucchi (University of Florence, Italy), who led the expedition with co-chief scientist Kohtaro Ujiie (University of Tsukuba, Japan).

She added, “but what we don’t fully understand is how these factors interact with one another and if one may be more important than another in leading up to different magnitudes of earthquakes. This expedition provided us with crucial samples for answering some of these fundamental questions.”

More than 80% of global earthquakes above magnitude 8.0 occur along subduction zones. The Pacific Ocean is famous for these boundaries, known as convergent margins, which are found along the coasts of the East Pacific from Alaska to Patagonia, New Zealand, Tonga, Marianas all the way up to Japan and the Aleutians, making the margins of the world’s largest ocean basin a primary target for research into the triggering mechanisms of large quakes.

During four weeks at sea, the science party and crew successfully drilled four sites, recovering core samples of sand and clay-like sediment and basalt rock. In a preliminary report published this month, CRISP scientists say that they have found evidence for a strong subsidence, or sinking, of the Costa Rica margin combined with a large volume of sediment discharged from the continent and accumulated in the last 2 million years.

“The sediment samples provide novel information on different parameters which may regulate the mechanical state of the plate interface at depth,” said Ujiie. He adds, “knowing how the plates interact at the fault marking their boundary is critical to interpreting the behavior and frequency of earthquakes in the region.”

Vannucchi explains, “for example we now know that fluids from deeper parts of the subduction zone system have percolated up through the layers of sediment. Studying the composition and volume of these fluids, as well as how they have moved through the sediment helps us better understand the relationship between the chemical, thermal, and mass transfer activity in the seafloor and the earthquake-generating, or seismogenic, region of the plate boundary. They may be correlated.”

Cores from the CRISP Expedition are currently being further analyzed by different members of the research party at their home institutions. The scientists will meet beginning August 29 at Texas A&M University to share their initial results.

The CRISP Expedition is unique because it focuses on the properties of erosional convergent margins, where the overriding plate gets “consumed” by subduction processes. These plate boundaries are characterized by trenches with thin sediment cover (less than 400 meters), fast convergence between the plates (at rates greater than 8 centimeters per year), and abundant seismicity.

The seismically active CRISP research area is the only one of its kind that is accessible to research drilling. However, this subduction zone is representative of 50% of global subduction zones, making scientific insights gleaned here relevant to Costa Ricans and others living in earthquake-prone regions all around the Pacific Ocean. The recent Tohoku Earthquake in Japan was generated in an erosive portion of the plate interface.

Other geoscience research drilling programs, such as IODP’s Nankai Trough Seismogenic Zone Experiment (NantroSEIZE), near the southeast coast of Japan, focus on accretionary margins, where the front part of the overriding tectonic plate is built up by the subduction processes (sometimes forming mountains) and the plate boundary input is trench material. In these environments, the trench sediments are significantly thick (greater than 1000 meters or over a half a mile). Accretionary margins are known for their large earthquakes as the 1964 Alaska and the 2004 Sumatra quakes. Japan’s Nankai Trough itself was the center of two magnitude 8 earthquakes in 1944 and 1946.

The CRISP team hopes to return to the same drill site in the future to directly sample the plate boundary and fault zone before and after seismic activity in the region. Changes observed through this work may provide new insights into how earthquakes are generated.

Heavy metal meets hard rock: Battling through the ocean crust’s hardest rocks

350°C) water vents on the seafloor. – IODP/USIO”>
A granoblastic basalt viewed under the microscope (picture is 2.3 mm across). Magnification shows a rock formed of small rounded mineral grains annealed together (plagioclase: white, pyroxene: light green and light brown, and magnetite or ilmenite: black). They may look inoffensive, but these rocks are the hardest material ever drilled in more than four decades of scientific ocean drilling. The rocks are very abrasive and aggressive to the drilling and coring tools, and difficult to penetrate. However, the samples recovered provide a treasure trove of information, recording the rocks’ initial crystallization as a basaltic dike then their reheating at the top of the mid-ocean ridge magma chamber. These rocks represent the heat exchanger where thermal energy from the cooling and solidifying melt in the magma chamber below is exchanged with seawater infiltrating from the oceans, leading to the ‘black smoker-type’ hot (>350°C) water vents on the seafloor. – IODP/USIO

Integrated Ocean Drilling Program (IODP) Expedition 335 Superfast Spreading Rate Crust 4 recently completed operations in Ocean Drilling Program (ODP) Hole 1256D, a deep scientific borehole that extends more than 1500 meters below the seafloor into the Pacific Ocean’s igneous crust – rocks that formed through the cooling and crystallization of magma, and form the basement of the ocean floor.

An international team of scientists led by co-chief scientists Damon Teagle (National Oceanographic Center Southampton, University of Southampton in the UK) and Benoît Ildefonse (CNRS, Université Montpellier 2 in France) returned to ODP Hole 1256D aboard the scientific research vessel, JOIDES Resolution, to sample a complete section of intact oceanic crust down into gabbros.

This expedition was the fourth in a series and builds on the efforts of three expeditions in 2002 and 2005.

Gabbros are coarse-grained intrusive rocks formed by the slow cooling of basaltic magmas. They make up the lower two-thirds of the ocean crust. The intrusion of gabbros at the mid-ocean ridges is the largest igneous process active on our planet with more than 12 cubic kilometers of new magma from the mantle intruded into the crust each year. The minerals, chemistry, and textures of gabbroic rocks preserve records of the processes that occur deep within the Earth’s mid-ocean ridges, where new ocean crust is formed.

“The formation of new crust is the first step in Earth’s plate tectonic cycle,” explained Teagle. “This is the principal mechanism by which heat and material rise from within the Earth to the surface of the planet. And it’s the motion and interactions of Earth’s tectonic plates that drive the formation of mountains and volcanoes, the initiation of earthquakes, and the exchange of elements (such as carbon) between the Earth’s interior, oceans, and atmosphere.”

“Understanding the mechanisms that construct new tectonic plates has been a major, long-standing goal of scientific ocean drilling,” added Ildefonse, “but progress has been inhibited by a dearth of appropriate samples because deep drilling (at depths greater than 1000 meters into the crust) in the rugged lavas and intrusive rocks of the ocean crust continues to pose significant technical challenges.”

ODP Hole 1256D lies in the eastern equatorial Pacific Ocean about 900 kilometers to the west of Costa Rica and 1150 kilometers east of the present day East Pacific Rise. This hole is in 15 million year old crust that formed during an episode of “superfast” spreading at the ancient East Pacific Rise, when the newly formed plates were moving apart by more than 200 millimeters per year (mm/yr).

“Although a spreading rate of 200 mm/yr is significantly faster than the fastest spreading rates on our planet today, superfast-spread crust was an attractive target,” stated Teagle, “because seismic experiments at active mid-ocean ridges indicated that gabbroic rocks should occur at much shallower depths than in crust formed at slower spreading rates. In 2005, we recovered gabbroic rocks at their predicted depth of approximately 1400 meters below the seafloor, vindicating the overall ‘Superfast’ strategy.”

Previous expeditions to Hole 1256D successfully drilled through the erupted lavas and thin (approximately one-meter-wide) intrusive “dikes” of the upper crust, reaching into the gabbroic rocks of the lower crust. The drilling efforts of Expedition 335 were focused just below the 1500-meter mark in the critical transition zone from dikes to gabbros, where magma at 1200°C exchanges heat with super-heated seawater circulating within cracks in the upper crust. This heat exchange occurs across a narrow thermal boundary that is perhaps only a few tens of meters thick.

In this zone, the intrusion of magma causes profound textural changes to the surrounding rocks, a process known as contact metamorphism. In the mid-ocean ridge environment this results in the formation of very fine-grained granular rocks, called granoblastic basalts, whose constituent minerals recrystallize at a microscopic scale and become welded together by magmatic heat. The resulting metamorphic rock is as hard as any formation encountered by ocean drilling and sometimes even tougher than the most resilient of hard formation drilling and coring bits.

Expedition 335 reentered Hole 1256D more than five years after the last expedition to this site. The expedition encountered and overcame a series of significant engineering challenges, each of which was unique, although difficulties were not unexpected when drilling in a deep, uncased, marine borehole into igneous rocks.

The patient, persistent efforts of the drilling crew successfully cleared a major obstruction at a depth of 920 that had initially prevented reentry into the hole to its full depth of 1507 meters. Then at the bottom of the hole the very hard granular rocks that had proved challenging during the previous Superfast expedition were once more encountered. Although there may only be a few tens of meters of these particularly tenacious granoblastic basalts, their extreme toughness once more proved challenging to sample- resulting in the grinding down of one of the hardest formation coring bits into a smooth stump.

A progressive, logical course of action was then undertaken to clear the bottom of the hole of metal debris from the failed coring bit and drilling cuttings. This effort required the innovative use of hole-clearing equipment such as large magnets, and involved over 240 kilometers of drilling pipe deployments (trips) down into the hole and back onto the ship. (The total amount of pipe “tripped” was roughly equivalent to the distance from Paris to the English coast, or from New York City to Philadelphia, or Tokyo to Niigata). These efforts returned hundreds of kilograms of rocks and drill cuttings, including large blocks (up to 5 kilograms) of the culprit granoblastic basalts that hitherto had only been very poorly recovered through coring. A limited number of gabbro boulders were also recovered, indicating that scientists are tantalizingly close to breaking through into the gabbroic layer.

Expedition 335 operations also succeeded in clearing Hole 1256D of drill cuttings, much of which appear to have been circulating in the hole since earlier expeditions.

“We recovered a remarkable sample suite of granoblastic basalts along with minor gabbros, providing a detailed picture of a rarely sampled, yet critical interval of the oceanic crust,” Ildefonse observed. “Most importantly,” he added, “the hole has been stabilized and cleared to its full depth, and is ready for deepening in the near future.”

Hawaiian hotspot variability attributed to small-scale convection

Three-dimensional image showing predicted mantle temperatures (blue = warm, red = hot, white = hottest) and a plume of hot mantle rising beneath the Hawaiian hotspot. -  Maxim Ballmer, SOEST/ UHM
Three-dimensional image showing predicted mantle temperatures (blue = warm, red = hot, white = hottest) and a plume of hot mantle rising beneath the Hawaiian hotspot. – Maxim Ballmer, SOEST/ UHM

Small scale convection at the base of the Pacific plate has been simulated in a model of mantle plume dynamics, enabling reasearchers to explain the complex set of observations at the Hawaiian hotspot, according to a new study posted online in the June 26th edition of Nature Geoscience. “A range of observations cannot be explained by the classical version of the mantle plume concept,” says Maxim Ballmer, Post Doctoral Researcher in the Department of Geology and Geophysics in the School of Ocean and Earth Science and Technology (SOEST) at UHM. These observations include the occurrence of secondary volcanism away from the hotspot (e.g., Diamond Head, Punchbowl, Hanauma Bay), as well as the chemical asymmetry (Mauna Loa compared to Mauna Kea) and temporal variability (over timescales greater than 10,000,000 years) of hotspot volcanism itself.

Ballmer and colleagues, including advisor Garrett Ito, Associate Professor, in the Department of Geology and Geophysics in the SOEST at UHM, designed a geodynamic model of the mantle that successfully predicts a large range of observations thus providing insight into the composition and dynamics of the mantle. Ballmer says the findings of their model, “make an important contribution toward understanding the origin of volcanism away from plate boundaries. This is a long-standing question in our community that potentially provides general insight into the dynamics of our planet, and particularly into the make-up of the deepest mantle, from where mantle plumes originate. For many reasons, understanding the deepest mantle is relevant for questions about the early days of Earth, and the origin of water and life.”

These findings came as a bit of a surprise. Although small-scale convection was one hypothesis for explaining late-stage rejuvenated volcanism on the islands, Ito reports, “this study is the first to qualitatively explore this mechanism and to show that it can explain both rejuvenated as well as arch volcanism, well away from the islands.”

As a next step in understanding mantle dynamics, Ballmer hopes to explain some of the characteristics of the Hawaiian plume that have been revealed by SOEST – UHM colleague Cecily Wolfe using seismic earthquake tomography. To do this, he will simulate a thermochemical mantle plume, which in some ways behaves similarly to the upwellings in lava lamps. A thermochemical plume is a plume that is hot (i.e. thermally buoyant), but compositionally dense. Such a plume typically behaves more complicatedly than a classical plume.

The key role of the oceans’ subpolar regions in the climate control of the tropics is confirmed

An international team of researchers, led by the members of the Institut de Ciència i Tecnologia Ambientals (ICTA) at the Universitat Autònoma de Barcelona (UAB), has published the first registers of the evolution of Northern Pacific and Southern Atlantic sea-surface temperatures, dating from the Pliocene Era -some 3.65 million years ago- to the present. The data obtained in the reconstruction indicate that the regions closer to the poles of both oceans have played a fundamental role in climate evolution in the tropics.

This research solves another piece of the jigsaw puzzle that is the study of oceanic behavior and its influence on climate. The results are based on the doctoral thesis presented by Dr Alfredo Martínez-García (currently, a researcher with both the Swiss Federal Institute of Technology, ETH Zurich, and with the DFG-Leibniz Centre at the University of Postdam, Germany). The thesis was undertaken at the UAB and directed by Dr Antoni Rosell Melé, an ICTA ICREA researcher and adjunct professor with the Department of Geography. This work was carried out in collaboration with Dr Gerald H. Haug, of ETH and DFG-Leibniz Centre; Dr Erin L. McClymont of Newcastle University (UK); and Dr Rainer Gersonde, of the Alfred Wegener Institute (Germany).

The study of Pliocene climate has now been the object of intense research for several years, as this era represents-in the Earth’s history-the most recent climatic period in which, over a sustained period of time, average temperatures on the planet were significantly higher than those of the present. As a result, the Pliocene is thought of as a climatic period that might be representative of the Earth’s climate in future conditions of global warming.

In this study, the researchers analyzed marine sediment collected by the Integrated Ocean Drilling Program (an international initiative), and measured its composition of organic compounds termed alkenones.

Reconstruction of the surface temperature in the Northern Pacific and Southern Atlantic has enabled a simultaneous sea-surface cooling to be identified in the subpolar regions of the two hemispheres in the period between 1.8 and 1.2 million years ago. This finding coincides in time with the formation of the equatorial Pacific cold tongue-which currently almost disappears during the “El Niño” phenomenon.

Previous studies have shown that, during the warm conditions of the Pliocene, this cold tongue was not present; thus, conditions in the equatorial Pacific were similar to those of a permanent “El Niño” episode. Data obtained in this study indicate that the cooling and expansion of polar waters towards the tropics intensified atmospheric circulation. And this fact played a fundamental role in the equatorial Pacific, leading to the reduction in depth of the thermocline-the layer of ocean water in which the temperature fall rapidly-and therefore to the appearance of the equatorial cold tongue that we can currently observe.

The research undertaken provides empirical evidence, previously suggested by studies using climatic models, that the oceans in high latitudes may play a key role in the control of tropical climate and, most especially, in the thermocline depth in the equatorial Pacific.

The study contributes to the debate on which regions on the planet are those that, when their local climates change, give rise to processes of global change. It is often indicated that these regions are found in the tropics, since, when phenomena such as “El Niño” occur, they have global repercussions. This study provides evidence for the key role that may be played by the polar regions of the planet.

Currently, high latitudes are the ones that appear to be responding in the clearest way to global warming. Given the direct relationship established in this study between high-latitude climate variation and thermocline depth in the equatorial Pacific, it appears possible that the equatorial Pacific cold tongue will eventually respond to the current warming, giving rise to a climatic scenario similar to that of the Pliocene.

ROV images the discovery of the deepest explosive eruption on the sea floor

Oceanographers using the remotely operated vehicle (ROV) Jason discovered and recorded the first video and still images of a deep-sea volcano actively erupting molten lava on the seafloor. Jason, designed and operated by WHOI for the National Deep Submergence Facility, utilized a prototype, high-definition still and video camera to capture the powerful event nearly 4,000 feet below the surface of the Pacific Ocean, in an area bounded by Fiji, Tonga and Samoa.
Oceanographers using the remotely operated vehicle (ROV) Jason discovered and recorded the first video and still images of a deep-sea volcano actively erupting molten lava on the seafloor. Jason, designed and operated by WHOI for the National Deep Submergence Facility, utilized a prototype, high-definition still and video camera to capture the powerful event nearly 4,000 feet below the surface of the Pacific Ocean, in an area bounded by Fiji, Tonga and Samoa.

Oceanographers using the remotely operated vehicle (ROV) Jason discovered and recorded the first video and still images of a deep-sea volcano actively erupting molten lava on the seafloor.

Jason, designed and operated by the Woods Hole Oceanographic Institution for the National Deep Submergence Facility, utilized a prototype, high-definition still and video camera to capture the powerful event nearly 4,000 feet below the surface of the Pacific Ocean, in an area bounded by Fiji, Tonga and Samoa.

“I felt immense satisfaction at being able to bring [the science team] the virtual presence that Jason provides,” says Jason expedition leader Albert Collasius, who remotely piloted the ROV over the seafloor. “There were fifteen exuberant scientists in the control van who all felt like they hit a home run. “

Collasius led a team that operated the unmanned, tethered vehicle from a control van on the research vessel and used a joystick to “fly” Jason over the seafloor to within 10 feet of the erupting volcano. Its two robotic arms collected samples of rocks, hot spring waters, microbes, and macro biological specimens.

Through its fiber optic tether, ROV Jason transmitted-high definition video of
the eruption as it was occurring. The unique camera system, developed and operated by the Advanced Imaging and Visualization Lab at WHOI, was installed on Jason for the expedition to acquire high quality imagery of the seafloor. The AIVL designs, develops, and operates high resolution imaging systems for scientific monitoring, survey, and entertainment purposes. AIVL imagery has been used in several IMAX films and hundreds of television programs and documentaries.

The video from the research expedition, which departed Western Samoa aboard the RV Thomas Thompson on May 5, 2009, was shown for the first time today at the American Geophysical Union fall meeting in San Francisco.

“Less than 24 hours after leaving port, we located the ongoing eruption and
observed, for the first time, molten lava flowing across the deep-ocean seafloor, glowing bubbles three feet across, and explosions of volcanic rock,” reported Joe Resing, a chemical oceanographer at the University of Washington and NOAA, and chief scientist on the NOAA- and National Science Foundation-funded expedition.

For more than a decade, monitoring systems have allowed scientists to listen for
seafloor eruptions but there has always been a time lag between hearing an
eruption and assembling a team and a research vessel to see it. This has meant
that scientists have always observed eruptions after the fact.

“We saw a lot of interesting phenomena, but we never saw an eruption because it
happens so quickly,” said Robert Embley, a NOAA PMEL marine geologist and co-chief scientist on the expedition. “As geologists, you want to see the process in action. You learn a lot more about it watching the process.”

The scientists involved in the expedition had praise for the people and the technology that helped bring that dream to fruition.

“I don’t think there are too many systems in the world that could do what Jason does,” said Embley. “It takes a good vehicle, but a great group of experienced people to get close [to an eruption], hold station, and have the wisdom to understand what they can and cannot do.”

The Jason team maneuvered the vehicle to give scientists an up-close view of the glowing red vents explosively ejecting lava into the sea- often not more than a few feet away from the exploding lava – and the ability to take samples.

Enhancing the experience was the ability to view the eruption in high-definition video. Designed to operate at depths of up to 7,000 meters, the unique still and video camera system acquired 30-60 still images per second, at the same time generating motion, high def video at 30 frames per second. The system uses a high-definition zoom lens – nearly twice the focal length of Jason’s present standard definition camera — that enables researchers to see up-close details of underwater areas of interest that they otherwise could not see.

“We were lucky to have those cameras on the vehicle. They are important to the science,” said Tim Shank, a WHOI macro-biologist on the expedition. “We use the high def cameras to try to identify species. They allow us to look at the morphology of the animals — some smaller than 3 or 4 inches long.”

“In terms of understanding how the volcano is erupting, the high frame rate lets you stop the motion and look to see what is happening,” said Resing. “You can see the processes better.”

The National Science Foundation funded the installation of the camera system for this expedition. The system is being tested in advance of a permanent upgrade in 2010 to the cameras on Jason as well as the manned submersible Alvin. Maryann Keith, of WHOI’s AIVL, Shank, and other scientists operated the camera system with the assistance of the Jason team during the expedition.

In addition to the benefits to science, the cameras will serve the added purpose of giving the public more access to seafloor discoveries.

“Seeing an eruption in high definition video for the first time really brings it home for all of us, when we can see for ourselves the very exciting things happening on our planet, that we know so little about,” Embley said.

Pacific tsunami threat greater than expected

The potential for a huge Pacific Ocean tsunami on the West Coast of America may be greater than previously thought, according to a new study of geological evidence along the Gulf of Alaska coast.

The new research suggests that future tsunamis could reach a scale far beyond that suffered in the tsunami generated by the great 1964 Alaskan earthquake. Official figures put the number of deaths caused by the earthquake at around 130: 114 in Alaska and 16 in Oregon and California. The tsunami killed 35 people directly and caused extensive damage in Alaska, British Columbia, and the US Pacific region*.

The 1964 Alaskan earthquake – the second biggest recorded in history with a magnitude of 9.2 – triggered a series of massive waves with run up heights of as much as 12.7 metres in the Alaskan Gulf region and 52 metres in the Shoup Bay submarine slide in Valdez Arm.

The study suggests that rupture of an even larger area than the 1964 rupture zone could create an even bigger tsunami. Warning systems are in place on the west coast of North America but the findings suggest a need for a review of evacuation plans in the region.

The research team from Durham University in the UK, the University of Utah and Plafker Geohazard Consultants, gauged the extent of earthquakes over the last 2,000 years by studying subsoil samples and sediment sequences at sites along the Alaskan coast. The team radiocarbon-dated peat layers and sediments, and analysed the distribution of mud, sand and peat within them. The results suggest that earthquakes in the region may rupture even larger segments of the coast and sea floor than was previously thought.

The study published in the academic journal Quaternary Science Reviews and funded by the National Science Foundation, NASA, and the US Geological Survey shows that the potential impact in terms of tsunami generation, could be significantly greater if both the 800-km-long 1964 segment and the 250-km-long adjacent Yakataga segment to the east were to rupture simultaneously.

Lead author, Professor Ian Shennan, from Durham University’s Geography Department said: “Our radiocarbon-dated samples suggest that previous earthquakes were fifteen per cent bigger in terms of the area affected than the 1964 event. This historical evidence of widespread, simultaneous plate rupturing within the Alaskan region has significant implications for the tsunami potential of the Gulf of Alaska and the Pacific region as a whole.

“Peat layers provide a clear picture of what’s happened to the Earth. Our data indicate that two major earthquakes have struck Alaska in the last 1,500 years and our findings show that a bigger earthquake and a more destructive tsunami than the 1964 event are possible in the future. The region has been hit by large single event earthquakes and tsunamis before, and our evidence indicates that multiple and more extensive ruptures can happen.”

Tsunamis can be created by the rapid displacement of water when the sea floor lifts and/or falls due to crustal movements that accompany very large earthquakes. The shallow nature of the sea floor off the coast of Alaska could increase the destructive potential of a tsunami wave in the Pacific.

Earthquake behaviour is difficult to predict in this region which is a transition zone between two of the world’s most active plate boundary faults; the Fairweather fault, and the Aleutian subduction zone. In 1899 and 1979, large earthquakes occurred in the region but did not trigger a Tsunami because the rupturing was localized beneath the land instead of the sea floor.

Prof Ron Bruhn from the University of Utah said: “If the larger earthquake that is suggested by our work hits the region, the size of the potential tsunamicould be signficantly larger than in 1964 because a multi-rupture quake would displace the shallow continental shelf of the Yakutat microplate.

“In the case of a multi-rupture event, the energy imparted to the tsunami will be larger but spread out over a longer strike distance. Except for the small communities at the tsunami source in Alaska, the longer length will have more of an effect on areas farther from the source such as southeastern Alaska, British Columbia, and the US west coast from Washington to California.”

Warning systems have been in place on the US western seaboard and Hawaii since the 1946 Aleutian Islands tsunami. Improvements were made following the 2004 earthquake under the Indian Ocean that triggered the most deadly tsunami in recorded history, killing more than 230,000 people.

Prof Shennan said: “Earthquakes can hit at any time of the day or night, and that’s a big challenge for emergency planners. A tsunami in this region could cause damage and threaten life from Alaska to California and beyond; in 1964 the effects of the tsunami waves were felt as far away as southern California and were recorded on tide gages throughout the Pacific Ocean.”

Dr George Plafker from Plafker Geohazard Consultants said: “A large scale earthquake will not necessarily create a large wave. Tsunami height is a function of bathymetry, and the amount of slip and dip of the faults that take up the displacement, and all these factors can vary greatly along the strike.

“Tsunamis will occur in the future. There are issues in warning and evacuating large numbers of people in coastal communities quickly and safely. The US has excellent warning systems in place but awareness is vital.”

Marine scientists to investigate role of equatorial Pacific ocean in global climate system

In early March, an international team of scientists will set sail aboard the drill ship JOIDES Resolution on the first of two Integrated Ocean Drilling Program (IODP) expeditions to the equatorial Pacific Ocean.

The second expedition will follow immediately afterward in May. Both are grouped into one science program, known as the Pacific Equatorial Age Transect (PEAT).

The results will lead to a clearer understanding of Earth’s climate over the past 55 million years–a vital component to knowing what future course the planet’s climate will take, scientists believe.

“These expeditions focused on climate change come at a critical time,” said Julie Morris, director of the National Science Foundation (NSF)’s Division of Ocean Sciences, which supports IODP. “During the next year, sea-floor drilling related to climate change will happen from pole to pole.”

The PEAT expeditions aim to recover a continuous Cenozoic record (from 65.5 million years ago to the present) of sediments beneath the equatorial Pacific Ocean. Geologists will drill into the crust on the Pacific tectonic plate along the equator.

The first research effort, Expedition 320, is planned for March 5 through May 5, 2009; Expedition 321 will take place from May 5 through July 5, 2009.

Co-chief scientists of Expedition 320 are Heiko Palike of the University of Southampton, U.K., and Hiroshi Nishi of Hokkaido University in Japan; of Expedition 321, Mitch Lyle of Texas A&M University in the U.S., and Isabella Raffi of the Universita “G. D’Annunzio” Campus Universitario in Italy.

Earlier scientific ocean drilling expeditions to the equatorial Pacific yielded discoveries about past climate conditions and the past position of the Pacific tectonic plate relative to the equator.

However, they did not obtain continuous sediment records the two PEAT expeditions will recover seafloor sediment cores with an unbroken record.

“The cores will help us understand how and why productivity in the Pacific changed over time,” said Morris, “and provide information about rapid biological evolution and turnover during times of climatic stress.”

The equatorial Pacific is a major center of solar warming, a region of high productivity, and a primary region for carbon dioxide exchange from the deep ocean to the atmosphere.

It is also the source region for the El Niño-Southern Oscillation phenomenon. The equatorial Pacific also helps maintain global climates, and drives climate change.

Over the last 55 million years, global climate has varied dramatically from extreme warmth to glacial cold. These climate variations have been imprinted on the biogenic-rich sediments that accumulated in the equatorial zone.

Information from the PEAT expeditions will help scientists understand how Earth was able to maintain very warm climates relative to the 20th century, even though solar radiation received at the earth’s surface has remained nearly constant for the last 55 million years.