Amy Hessl is featured on National Geographic radio about our team’s discovery of ancient deadwood that suggests the rise of Chinggis Khaan was associated with increased rainfall. Listen to learn more.
Academic vessels operate throughout the year, and research cruises are scheduled during seasons when the weather is good enough for scientific operations. I am lucky to have research targets in tropical latitudes; the downside is that cruises to these regions are often scheduled when the weather is poor at higher latitude – in this case, smack during the holidays.
With round-the-clock shifts, there are precious opportunities for Santa to slip onto a research ship unseen. But slip in he did, leaving treats and gifts around the R.V. Langseth to brighten our day. In the main science lab, the midnight shift’s usual stash of Starbursts and Sour-Patch Kids expanded into a orgy of Pringles, summer sausage and pepperjack cheese, chocolate-covered Pretzels, and a six-pound bag of Gummy Bears. My Charlie-Brown Christmas tree suddenly blossomed with ornaments, from simple paper snowflake cut-outs to handmade fish spun from copper wire snagged from the electrician’s shop. Beautiful paper wreathes appeared on several cabin doors. Over in the OBS lab, Santa delivered a set of pop guns with rubber darts; after briefly considering storming the bridge, the boys entertained themselves with target practice while retrieving the last instrument.
Christmas dawn broke slightly cloudy as we steamed into our last task of the experiment, checking on the status of one of the instruments that we will leave in place for a year. As we finished this task, the sun burst through into a brilliant blue sky — certainly not a white Christmas, but welcome nonetheless. The scientific party and crew mustered outside for the requisite cruise photo, bedecked in holiday cheer. It was time to turn for home.
The festivities of the day were tempered by a degree of melancholy at the thought of loved ones back at home, enjoying their own holidays in our absence. The Lamont Marine Office opened up the satellite phone lines, giving everyone a 15-min phone call, and the chatter from those calls resonated through the ship. As scientists, we have been given a remarkable opportunity to explore our planet and unravel its mysteries. Making that happen requires hard work and sacrifice – from the talented crew around us, from our families back home, and from ourselves. We are truly thankful for that opportunity.
Over the first 22 days aboard the R/V Marcus G. Langseth, we’ve zigged and zagged our way over a 360×240 mile region of the Pacific plate, first dropping instruments to the seafloor, and then shooting airguns to them (see previous posts). The final step is to recover a subset of the instruments: 34 ocean-bottom seismometers (OBS) that recorded the shooting, and three of the MT instruments. Excitement abounds – we will see our new data for the first time when we pick up the instruments, and get enticing first peeks that may confirm our ideas about plate structure. But there is plenty of apprehension as well; many potential obstacles are associated with recovering our instruments from the seafloor, and it is possible that some of them (and the data that they contain) could be lost permanently to the deep.
Much of the apprehension is stimulated by uncertainty in the communication with the instrument. As we arrive at each site, we send acoustic “pings” from a transmitter on the ship, asking the instrument to wake up; if the instrument is alive, it will ping back. A second set of pings instructs the instrument to release its anchor, a process that typically takes several minutes. Subsequent pings to the instrument allow us to estimate the distance to it and thus whether or not it is rising to the surface. In shallow water, this system works great. But at 5 km water depth, transmitting acoustic signals is akin to operating a TV remote with a weak battery from across a large crowded room. Signals are faint, and echoes from the ship and other noise sources mask the instrument signals, such that we were often unsure if the instrument was responding or not. The uncertainty was maddening.
Despite these uncertainties, the instruments did indeed hear our distant acoustic calls. The first several recoveries went well, and the data look excellent. However, we then encountered a string of three consecutive instruments that refused to budge from the seafloor. All responded to our pings, but they could not lift off the bottom. Stuck in the mud? Flooded? After spending several hours attempting to recover them, we sadly moved on. Forensic analysis of some of the recovered instruments revealed a likely cause: bad AA battery cells in the release systems, such that they have power to communicate, but not quite enough to complete the release process. Recognizing this, we devised a power-saving routine for the remainder of the recoveries; sending release commands in brief bursts that used minimal power, and then waiting in near-silence until the OBS appeared at the surface. This proved successful, and in the end, we recovered 30 of 34 OBS, and 2 of 3 MT instruments. We are frustrated by the losses, but thankful for the data in hand. Next year we will return to recover the broadband OBS that are recording the earthquake data – in the meantime, we hope to engineer a new plan to coax the four missing OBS back to the surface.
The NoMelt experiment aims to image the structure of an oceanic plate, including its deepest reaches up to 70 km beneath the seafloor. One of our primary means to do so is to create sound (acoustic) waves in the ocean from the ship, and record those waves at receivers on the seafloor, after they have traveled 10’s-100’s of miles through the rocks that underlie the ocean basin. The R/V Langseth is equipped with a large airgun array, which is capable of producing such sounds.
Each airgun consists of a steel cylinder that can hold a large volume of compressed air. When fired, the gun forces the air into a bubble in the water, which quickly pops and collapses under the water pressure. The “bang” associated with the collapsing bubble travels efficiently through the water, and when it reaches the seafloor, much of the sound energy converts to seismic waves that travel through the crust and mantle. With a single airgun, the sound is loud enough to penetrate only into the upper layers of sediment beneath the ship. We can crank up the volume by firing multiple guns at once, allowing the energy to travel deeper into the Earth and to greater distances. During NoMelt, the Langseth tows an array of 36 airguns that produce sufficient energy to probe well into the oceanic plate and travel back up to receivers deployed several hundred km away on the seafloor (see my previous post).
But just being loud is not sufficient. Simply shooting all the guns at once will produce a loud but “ringy” sound, in much the same way that turning a stereo up to maximum volume (11!) will distort the music. The Langseth’s airgun array is “tuned” to produce the ideal sound for our purpose. In practice, this means firing the guns microseconds apart, such that they interfere to produce a sharp, clean sonic pulse, rich in the low frequencies (think bass, rather than treble) that penetrate most effectively into the Earth. The array is also oriented to direct these pulses downward into the seafloor, rather than in all directions into the surrounding ocean. Finally, we fire the guns only once every 4 to 5 minutes, much more slowly than most seismic surveys. This allows the noisy echoes within the water column to die away, even out at the most distant instruments. This is critical for detecting the subtle lower amplitude arrivals returning from deep in the plate.
Over 11 days, we traversed 1000 miles of the ocean floor, traveling at 4 mph, shooting every 4 to 5 minutes, 24 hours a day. Student watchstanders and technicians continuously monitored the computers controlling the shooting. Protected species observers also worked around the clock, searching for nearby marine mammals (whales, dolphins) and protected sea turtles that may be sensitive to the noise. This is only a concern within ~1000 meters of the ship, but to be safe we monitor and report any activity up to four times this distance. In 11 days, we only encountered one small pod of sperm whales; when they meandered too close, we shut down our operation until they left the area, and then circled around and restarted the survey.
If all goes well, the recordings of these shots on the ocean bottom seismometers (OBS) will provide a truly unique portrait of the deeper (mantle) portion of the oceanic plate. This structure has not been comprehensively explored since the pre-airgun 1970’s, when large explosives tossed off the ship (essentially scientific depth charges) served as the sound source. Instrumentation and analysis tools have improved immeasurably since then. We now need to retrieve our OBS…
Oceanic plates are born at mid-ocean ridges, where hot mantle rocks are brought very close to the surface, partially melt, and then cool and crystallize. The newly formed rocks move outwards from the mid-ocean ridge, making way for the next batch of hot rock rising from below. Inch by inch, over millions of years, oceanic plates progress through a life cycle of birth at the mid-ocean ridge, cooling and aging in the open ocean basins, and destruction at a subduction zone, where they dive back into the mantle.
Because rocks contract inward as they cool, oceanic plates deepen considerably with age: from approximately 2500 meters depth at mid-ocean ridges to as much as 8000 meters depth in subduction-zone trenches. The NoMelt study region has matured to a middle-aged 70 million years (a plate age roughly equivalent to 40 human years), and sits at a seafloor depth of just over 5000 meters. That’s 3 miles of seawater, with the temperature at the bottom just above freezing – a very inhospitable environment to deploy our seafloor equipment.
Four days after departing Honolulu, we began deploying ocean-bottom seismometers (OBS) and seafloor MT instruments, over a grid spanning 360 miles by 250 miles. The instruments come in four flavors, designed for different types of measurements, but they have several components in common. First, they all deploy via “free fall” – they are hoisted over the side of the ship using a crane, and dropped into the water. They weigh several hundred pounds each and sink to the bottom within a few hours. Each contains a sensor such as a seismometer or a magnetometer, a low-power computer to record the data, and acoustic transceivers capable of receiving and replying to simple commands, such as “turn on” or “reply to this ping.” All are stocked with a battery supply capable of running the instrument for the duration of the experiment – up to a year for some instruments. All of these electronic components are housed in precisely engineered aluminum tubes and glass and titanium spheres designed to withstand the crushing pressures at 6000 meters below the sea surface.
Our deployment strategy poses some risks. We cannot ensure they land nicely in good spots on the seafloor. The combination of pressure and corrosion continuously wears on the instrument over a year-long deployment, and it can be difficult to withstand. If a problem occurs, then the instrument and any data it contains may be lost. And problems do occur – glass spheres implode, aluminum cases corrode and leak, instruments can float prematurely to the surface because they accidentally release from their anchors.
Tiny “upgrades” in instrument design can prove catastrophic. In one legendary case, a new disk drive was just heavy enough to make the anchorless instruments neutrally buoyant; instead of floating to the surface at the end of the experiment, they hovered 10 meters above the seafloor, never to be seen again. But there is no affordable alternative for deploying equipment on the seafloor in the open ocean, and over the last 15 years, the seafloor geophysics community (see www.obsip.org) has learned many lessons for minimizing the risk.
Working around the clock for four days, our team of technicians (from Scripps Institute of Oceanography and Woods Hole Oceanographic Institution), students, and PI’s deployed 61 OBS and nine MT instruments. Our time is tight, so we dropped them over the side and moved quickly to the next site, never knowing whether they reach a safe resting place on the bottom.
In a little over a week, we will return to recover 34 of the OBS (short-period instruments designed specifically to record the airgun shots from the Langseth) and two of the MT instruments. Only at that point will we truly learn if the deployment has been successful. We will not know the fate of the remaining 27 OBS and seven MT for another year.
The post Deploying Instruments on the Seafloor in the Deep Ocean appeared first on State of the Planet.
We nicknamed our project NoMelt because we seek to characterize a mature, pristine oceanic plate far from its volcanic origin at a Mid-Ocean Ridge, and away from areas of pronounced volcanism and melting that subsequently alter the structure of the plate. Our site in the central Pacific fits these scientific needs. However, one downside is that four days of transit are needed to reach this area from Honolulu. Research ships travel at 10 knots (a whopping 12 MPH) – who knew that ships were so slow? Our science party filled these days acclimating to life at sea – typically hunkered down in our bunks, sleeping-off the motion sickness and the drugs used to treat it. Many of us had envisioned calm waters in the tropical Pacific and hoped to avoid this initial bout of sea-sickness. But as we cleared the lee of the islands, 45-knot winds and 5-meter seas quickly disabused us of this fantasy. Two days out, the winds dropped and the seas subsided into a more comfortable roll, and we emerged to get to work.
We stepped directly into the bustle of a large oceanographic research vessel at sea. The R/V Langseth operates continuously for weeks at a time all over the globe. Our 34-day cruise requires a crew of 47, including 13 of us in the science party – sea-going temps who provide the scientific oversight and manpower necessary for this particular experiment. The permanent crew are talented and dedicated, with the full gamut of skills necessary to keep a large, complex vessel safe and operational in the open ocean: mechanical, electrical, navigational, computational. They keep the massive diesel-electric engines running smoothly, rewire cranes and rigs, repair and retool seismic airguns and streamers, and debug the network and internet services required to collect our data (and email home!). Because we are using loud sound sources in the water, the staff includes protected-species observers (PSO’s), who monitor for nearby whales, porpoises, and sea turtles that could be harmed if they venture too close to our airguns. Shipboard scientific operations continue 24 hours a day, and everyone has a role and a duty to make this possible.
Next up – seafloor deployments….
Everything that we understand about the rhythms of the Earth’s surface – the slow growth of mountain chains, the creeping expansion of the ocean basins, the abrupt upheaval of a major earthquake, the explosive eruption of a volcano – is viewed through the context of plate tectonics. This simple yet highly successful model for describing processes at Earth’s surface rests on two notions: (1) the outer shell of the Earth is broken up into nearly rigid blocks, or “plates”, ranging in thickness from a few 10’s to a few 100’s of kilometers; (2) nearly all the geologic activity such as faulting and volcanism happens in very narrow zones at the boundaries between these plates. As a result, Earth scientists generally focus on understanding faulting and volcanism at plate boundaries. But to understand what happens at the contacts between plates, we need to address an underlying question – what is a plate? Or more specifically, what critical processes allow the rock within the plate to behave very rigidly, in sharp contrast to the weak rock beneath the plate’s base, or along its margins?
On the Saturday after Thanksgiving, a team of scientists departed Honolulu for a remote portion of the central Pacific Ocean on the research vessel R/V Marcus G. Langseth in search of answers to this question. Our target is a swath of seafloor approximately 1200 miles southeast of Hawaii (see map). We chose this area because it contains some of the oldest oceanic crust on the planet and it has not been modified by other volcanic activity since it was formed 70 million years ago. We hope that the structure of this mature, pristine oceanic plate can illuminate the most basic aspects of plate formation and evolution.
After a four-day steam, we will arrive at our study area armed with a suite of geophysical tools to image the oceanic plate in this region with unprecedented precision and scope. We will toss 61 ocean-bottom seismographs (OBS) overboard in 5000-meter-deep water over a 600-km by 400 km area. OBS sink slowly to the seafloor and autonomously record sound waves from natural and man-made sources. Some of these sensors will remain on the bottom for over a year, recording the shaking from distant earthquakes. The remainder will record sound waves generated using large airguns towed in the water behind the ship and will be recovered at the end of this cruise. Simultaneously, we will record sound waves reflecting back from beneath the seafloor on an 6-km-long “streamer” containing hundreds of seismic sensors that we tow behind the ship. Finally, we will deploy a set of instruments designed to measure the electrical and magnetic fields at the seafloor. This combination of instruments will provide detailed information on the seismic wavespeed and electrical conductivity structure through the oceanic plate, which we will use to constrain the rock properties that control plate behavior. The experiment is funded by the U.S. National Science Foundation.
Seagoing research is an exciting but stressful business, and this cruise is no exception. In particular, the large water depths put tremendous pressure on seafloor instruments, increasing the risk of loss. In addition, the research activities are highly choreographed, and even modest difficulty with equipment or weather can compromise the experiment. But we are optimistic that this program will yield fundamental new insights on a core aspect of our paradigm for Earth processes. Over the next 30 days, I will provide regular updates on the project – both the day to day rhythms of life at sea, and the exciting science that will follow.
By Kirsty Tinto & Mike Wolovick
As little as a few decades ago you could ask a scientist what it was like to monitor the changing ice in Antarctica and the response might have been “Like watching paint dry” — seemingly no change, with no big surprises and not too exciting. Well times have changed. The Ice Bridge Mission is deep into its third Antarctic season collecting data on the condition of the continental scale ice sheet and the floating sea ice that surrounds it, and has noted some exciting results.
On a recent survey flight, which was designed to be fairly routine flying back and forth across the main trunk of Pine Island Glacier, a large crack was spotted in the floating ice tongue in the front of the glacier — a crack large enough to bury a building 16 stories high. This means more changes are coming in the future of this active ice stream.
Pine Island Glacier has been under intense focus as one of the fastest moving, and rapidly thinning glaciers in Antarctica. The planned survey was a grid back and forth across the main trunk of Pine Island Glacier. The pilots refer to this kind of survey as “mowing the lawn.” This type of data collection is essential for putting together a more complete “picture” of the glacier surface, depth, and its underlying surface, and its “grounding line.” The grounding line, shown here as the white line running through the image of the survey plan, is the front edge of where the glacier is frozen all the way to the bottom surface beneath it. The glacier extends beyond the grounding line but as a “floating tongue” of ice.
Glacial tongues can be many meters thick, but because they rest on water they are susceptible to warming from the water below. It is not unexpected for sections of the tongues of glaciers to break off – in fact for this glacier scientists expect to see it occur about twice a decade (the last notable occurrence was in 2007). It is, however, impressive to see it actually developing, and to realize the scale of the crack as it begins – at least 50 meters deep, and up to 250 meters wide. Yes this is much better than watching paint dry.
Lamont-Doherty Earth Observatory has been a partner in this NASA led project collecting airborne gravity. The Ice Bridge Mission is designed to fill the gap between two satellite missions, IceSat I and IceSat II, collecting data on ice thickness in both polar regions. IceSat II is intended to be in orbit in another 4 to 5 years.
By Neil Pederson
As discussed in the previous post, the first half of the field season would be the scientific highlight of the 2011 field season. While we had highlights later on, in terms of finding new stuff, that was it. We knew that would be a highlight because we had a fairly good idea of what was coming next. To our delight, we would be heading back to the small mountain village called Bugant. This is a delight because the family we stay with on trips to the northwestern Khentii Moutains are exemplary in terms of Mongolian generosity.
We knew that we would immediately not only be served fresh tea and plenty of candies and snacks upon our arrival, we also knew that no matter what time ae arrived we would be served a meal. We arrived at about 9 pm and, sure enough, by 9:45 we were fully into our meal.
As always, it was a fun and spirited meal. All the extended family came to visit with us and each other:
We looked forward to the next day’s field work because we were going to one of the most interesting forests we’ve seen in Mongolia – it was an intact, old-growth forest….
However, not all scientific fieldwork is full of exploration and discovery like those fueled by sawdust and mosquito wings. Sometimes, quite often actually, scientific research is monotonous. Even in the field. The work ahead, while in beautiful places, was akin to making the doughnuts. We had to go back to areas we had sampled before, install plots and just core whatever trees fall in those plots. There would be no bird-dogging or seeking out great old trees. What fell in our plots, randomly-located so that they best represented the average forest, ended up being our study trees. Ah, we are not complaining. It is just not as thrilling as the hunt. It feels almost industrial – industrial ecology.
We were a bit leery of this forest as well. When we last sampled in 2009, it turned out to be a cold and wet visit. 2011 turned out to be very much the same. In fact, it turned out to be wetter and colder. It definitely had us shivering in our sleeping bags.
We had expected to complete our work in the first day at the site pictured above. But, after a couple passing showers that were fairly heavy for Mongolia, the temperatures dropped quickly and, well, we started getting cold. We were prepared for this, but somehow this day got to us. We really started shivering and making mistakes. When you start making mistakes when you are cold and wet, that is a good sign to call things off. Not much good can come from continuing. What one can expect is potentially bad data, more mistakes and more mistakes that could become dangerous. So, we called it a day and went fishing.
OK, Baljaa went fishing. Specifically, he went wood fishing. It is a method commonly used to gather firewood in areas with little wood. As you can see, Baljaa, despite being a Mongolian cowboy with more than a hundred horses [he’s a good catch, ladies!], struck out. Time to call in the pro:
As you can see, Baatarbileg is still the master!
What did we cook with this wood? Our clothes, of course:
Actually, the fire and wonderful soup for dinner warmed us up. I do not think the devil actually shivered in his sleeping bag.
The next day turned out to be sunny and we finished off this site. We did get one new discovery: a Mongolian lizard. It got so used to being held, or perhaps it was so hungry from the previous cool, wet day, it itself ‘fished’ for food while being held:
The next day found us heading back to the ‘cement patio’ site. This is a favorite site for us as we had a wonderful Mongolian cookout in 2009. What we had forgotten was how far back we had driven into the Khentii Mountains to find this site.
Talk about monotonous [and desperate…like the beginning of 2011, we were desperate in 2009 to find a goldmine site], we drove 20 km on the road below just to find this site. You can hear below how we had forgotten how far back we drove in 2009.
We hit the slopes as soon as we re-discovered the cement patio; it took about 3 hrs of driving to get to this spot. I had not been up this slope yet as I sampled a different slope in 2009. When Amy said it was steep, I really didn’t know what she meant. As you can see, the slope was nearly a 40% slope:
While in the midst of conducting this industrial ecology, the sky decided to open up again. However, the storm didn’t seem as serious as the prior day and we hunkered down for about 20 minutes. Sure enough, the storm passed as we completed most of our work at this site.
The views from this site are pretty spectacular.
Indeed, it is such a special forest that we will have a special post regarding the state and potential future of this part of the Khentii Mountains.
We headed down the mountain back to the patio and found an incredible patch of berries. There were two types of currants and one type of blueberry. It was delicious. In fact, as it was Chuka’s birthday (our other driver in 2009 and 2011), we gathered as much fruit as possible and re-created our 2009 cook out night to celebrate Chuka. It was a fantastic night until yet another thunderstorm crashed the party and sent us scurrying for the tents. All in all, it was a pretty great night.
There is not too much to report for now about this site. It is definitely another old-growth site that Amy has already written about. We saw some amazing specimens for the main conifer species in Bugant and hiked some cool ridges. We saw wolf and bear scat. We were lucky to spend time in that exceptional Mongolian Wilderness. Here are a couple more pictures.
At 6:30 am on August 5, the R/V Langseth pulled into port in Dutch Harbor, marking the end of our very successful research cruise. Our steam into port from our study area involved a trip through Unimak pass and beautiful views of Aleutian volcanoes, including majestic Shishaldin.
Many things are required to make a research cruise successful, but one of the most important is the people. And we had great people in spades. The Langseth’s crew and technical staff are excellent: extremely competent, hard working and dedicated. Throughout our endeavor offshore Alaska, there were challenges: temperamental aging scientific equipment, tricky maneuvering very close to the coast line, subpar weather, etc. All of these obstacles (and more) were handled admirably and without complaints. Protected species observers cheerfully spent long, cold hours exposed to the elements on the observation tower watching for mammals to ensure that we operated responsibly. Our science party was also terrific; everyone worked hard and worked well together. And if you’re going to spend 38 days at sea with a group of people, it doesn’t hurt if they are nice and friendly in addition to being smart, competent and hard working. And it was a uniformly nice and friendly crowd aboard our cruise, MGL1110. Our efforts would also not be possible without support ashore from Lamont’s Marine Office and the National Science Foundation. The evening of our arrival in Dutch Harbor, we celebrated the completion of our successful cruise and toasted (repeatedly…) the people who made it possible at a post-cruise party at the Harbor View Bar and Grill.
Many people flew home after our arrival in Dutch Harbor, but not me! (At least not yet). Katie Keranen and I will recover the seismometers we deployed way back at the beginning of the summer. Hopefully these instruments recorded lots of earthquakes as well as our offshore experiment, and hopefully they were not disturbed or damaged by curious wildlife (including people!). An Anchorage-bound flight from Dutch Harbor dropped me off in Cold Bay on Aug 6, where I rendezvoused with Katie. After the plane landed, the stewardess asked for our “Cold Bay passenger” to disembark. Passenger. Singular. I filed past all the folks heading to Anchorage and beyond. Unlike them, I will linger a little longer on the beautiful Alaska Peninsula.
1 August 2011 – Final Dispatch from Arequipa, Peru
Now, after more than six weeks trawling the Peruvian Andes in search of palaeoclimate clues, we’re out of time. More than that, rather exhausted, too. Since we left Ampato, Matt has gone back to Tacoma, leaving Kurt and me to visit potential calibration sites near Coropuna. The objective of that ongoing work is to refine the cosmogenic surface-exposure method for the tropics, thereby improving the precision of new and existing datasets. It’s therefore a very high priority.
Many hours of rough driving over destroyed mining roads brought us finally to an isolated copper mine north of Coropuna. There, having waded through piles of bureaucratic red tape and caught a wretched cold from a forlorn security guard, I spent a few days exploring potentially suitable lava flows, while Kurt went off in search of palaeoindian lithics and rock shelters. It’s a fine spot, with amazing volcanic features and stunning views of Coropuna, and boasting more viscacha (a type of Andean rodent/rabbit/monkey mix) per square meter than anywhere else on Earth. It’s too early to say whether this area will prove useful, but the search itself certainly constituted a worthy adventure.
With our last samples collected and bagged, these last few days have been a whirlwind of tying up loose ends, such as returning the vehicle, shipping 100 kg of stones back to Lamont, and eating as much as possible. Arequipa is a lovely city, and a fine place to call base camp, but with so many chores to be done it was with a great measure of relief that we climbed onto the plane again at the foot of Volcan Misti, bound for Lima and, ultimately, the northern city of Huaraz. I could go on for pages about the splendours of that place, tucked up in the stupendous Cordillera Blanca, but I shall save it for another year. As for now, I shall swap icy peaks, tents, and blue skies for the record-setting heat of urban New York, while Kurt heads back south to Arequipa for a while longer to complete archaeologic lab work there. This has been a fantastic season, our most successful yet – I hope you’ve enjoyed following along from a safe distance.
Although we still have ~3 days of data collection aboard the R/V Langseth to go before we pull in our equipment and head for port, we are already drowning in beautiful seismic data. Following each pulse from the air gun array, the two 8-km-long streamers listen for returning sound waves for 22 seconds. This is enough time for the sound waves to travel down through the water, sediments, crust and upper mantle and back again. Arriving sound waves are recorded on a total of 1272 separate pressure sensors along the streamers, producing about 60 Mb of data for each pulse. Repeat this every 25 seconds for 3 weeks, and you end up with a pile of data! We have already recorded over 2.5 terabytes (2500 gigabytes!) of raw seismic data. This does not include other large datasets that we are simultaneously acquiring, such as detailed bathymetric mapping of the seafloor.
Once we obtain the raw data, our eager scientific party cannot resist beginning some rudimentary analysis, thereby generating even more large data files that take up yet more disk space. In search of instant gratification, we use some quick and dirty processing steps to produce preliminary images from our data and get a first peek at the structures beneath the seafloor. This is standard procedure on cruises aboard the Langseth and other seismic ships. Often, such images reveal very little; careful analysis of seismic data to create clear and accurate images of earth structures takes years. But in our case, the data are of such high quality that spectacular features are evident even in these rough first images, including the plate boundary and other faults. This assures us that hard work on the data following the cruise will produce very exciting results.
One of the key shipboard tasks is determining the position of the gear in the water and combining this navigational information with the raw data. Our streamers are 12 m under the sea surface, so we cannot simply attach tons of GPS sensors to them to figure out where they are at any given time. Instead, the Langseth’s infatigable Chief Navigator, David Martinson, works out the locations of the streamers using GPS’s at the beginnings and ends, a series of compasses spaced along the streamers, and several “acoustic nets,” sets of instruments that give the distances between the streamers at key positions. He can determine the positions of our two unruly 8-km-long cables to within ~5 m or less at any given time – amazing!
We also produce initial images of seafloor topography from bathymetry data. At sea we begin the arduous task of manually editing vast quantities of the data, but the effort pays off. Careful analysis of these high-resolution data can reveal faults that cut through the seafloor, seamounts, and sedimentary features.
20th July – Dispatch from Nevado Ampato, Andes
Our camp is at 5045 m on the dusty slopes of Ampato, an extinct, ice-clad volcano in the Western Cordillera. This is the very mountain from which Juanita, the famous Incan ‘ice maiden’, was plucked back in 1995. The tents are clustered in the lee of a large glacial erratic and, now the clouds have cleared, the view is second to none, taking in the dry plains far below and myriad volcanic peaks in every direction. Of these, only distant Ubinas shows any activity, letting slip the occasional cloud of ash. To complete the picture, behind us are the hulking masses of 6380 m-high Ampato and it’s smaller yet more violent brother, Sabancaya.
Yes, it is a fine place to call home as we begin mapping and sampling moraines of late-glacial and Holocene age in this part of the world. For added interest, the landscape here is dominated by sinuous lava flows that extend many kilometres from Sabancaya’s summit to the puna below. These black tongues of rock are both grotesque and strangely beautiful, especially when dusted with snow.
Speaking of dust, or rather sand, recently it has become a bit of a plague. Given the propensity for volcanic activity in this part of the Andes, our peaks camp is located on a surface of black sand, dust, and gravel, much of which becomes airborne during the fierce wind storms we’ve been experiencing. Just yesterday, as we were working on the youngest and highest moraines on Ampato, we happened to be suffering through a particularly bumpy spell of weather.The wind was funnelling down from the peak and pushing around waves of drifting snow. It was truly invigorating! From our high perch, though, we watched as plumes of dust were lifted by the wind from the plateau below, forming a brown blanket that came to obscure all but the highest peaks before spreading south to torment the city of Arequipa. By the time we returned to our camp that afternoon, our world was one of particulate matter. Sand in our food, sand in our tents, sleeping bags, and clothes. Worst of all, there was sand in my tea. But then, they always did say it takes a lot of grit to be a glacial geologist.
For the last nine days, we have been underway acquiring seismic reflection data to study a plate tectonic boundary offshore Alaska with the R/V Marcus G. Langseth. Now that the initial excitement of deploying all of our seismic gear and watching the first sound waves arrive on our two 8-km-long streamers has faded, we have settled into a routine of watches and standard shipboard data processing. Meals, sleep and leisure also take on predictable patterns. Each day resembles the one before, and they all start to blend together. This may sound rather humdrum, but an uneventful day at sea is normally a successful and productive one (as one of the undergraduate watchstanders noted). When something “exciting” happens, it is usually not good.
Happily, a large proportion of our nine days have been blissfully boring, but we have had our share of happenings. Excitement takes the form of equipment failures, bad weather and marine mammals. Acquiring marine seismic reflection data is a fantastically complex undertaking involving a lot of sophisticated, interdependent gear, so things can and do go wrong once in a while. A few nights ago, one of our streamers sank too deep, causing a “streamer recovery device” (a specialized airbag) to deploy and float the streamer to the surface. The next morning, a team used the workboat to visit the problematic streamer section and remove the airbag. On a few other occasions, I have received phone calls in the middle of the night summoning me from my cabin to the main lab to discuss other equipment hiccups – no one ever calls at 3 a.m. to let you know that everything is going swell.
Whales are beautiful and majestic, and we have been treated to numerous sightings, but we try to keep our distance. Since we are creating sound waves to image the earth, and marine mammals use sound to navigate and communicate with one another, our activities might disturb them. A team of protected species observers (PSO) watches for mammals, and we suspend operations if a mammal comes too close. Yesterday morning, we found ourselves surrounded by three species of whales, including a rare Northern Pacific Right Whale – an amazing sight, but it prevented us from collecting data for nearly four hours.
Of course there are notable exceptions to the “excitement is bad” maxim, the most important of which is the science! We use our new data to create very preliminary images of the structures below the seafloor as we go, and they have revealed some intriguing and surprising features. A regular sight in the main lab is a group of people gathered around a computer screen or a large paper plot, talking and pointing excitedly. We have a lot of hard work ahead after the cruise to obtain concrete results, but it’s exhilarating to glimpse faults, sediments and other structures in our data for the first time and ponder what they might be telling us about this active plate tectonic boundary. Even after spending a total of nine months at sea on ten research cruises over my career, the excitement of new data has definitely not worn off.
One of the core objectives of our project is to image the part of the plate tectonic boundary that locks up and then ruptures to produce great earthquakes. In the Aleutian subduction zone, the Pacific plate is being thrust northwards underneath the North American plate. To examine deep parts of the interface between these plates, we need to go as far north (and as close to the coast) as possible. This is easier said than done. We are towing a lot of scientific equipment behind the ship, including two 8-km-long cables (streamers) filled with pressure sensors, so approaching the coast and making turns is complicated and requires special attention to safeguard our gear. The southern edge of the Alaska Peninsula is rugged and flanked by lots of small jagged islands and shallow features just below the surface of the ocean. Currents and water density can vary locally near the coast, which could affect the positions and depths of our streamers behind the ship. And there is more fishing activity close to the coast, and thus increased risk of tangling seismic gear with fishing lines and nets. To reduce the risk, we scouted all of the trickiest parts of our survey ahead of time before we deployed the streamers, and we monitor the currents and fishing as we approach the coast. Captain Jim O’Loughlin, Chief Science Officer Robert Steinhaus, and the Langseth’s other crew and technical staff have a tremendous amount of experience and skill in maneuvering in tight spots while towing seismic equipment.
We recently completed one of our closest approaches to land near Unga, one of the Shumagin islands. At the apex of the turn, our 8-km-long (5-mile-long) streamers came within less than a mile of the coast. Due to some early difficulties with our equipment and an abundance of marine mammals, we had to make several attempts to collect data on the landward part of the line (and thus several passes near the shoreline). I held my breath and watched our third (and final) pass from the bridge. After the ship and gear passed safely through the most harrowing part of the turn, the captain turned to me and asked, “We’re not going to do this again, are we?” Thankfully not! At least not here. But there are several other important parts of our survey ahead that will require close approaches to the coast to image critical parts of the plate tectonic boundary. As with this near-shore encounter, we will rely on the skill and experience of the mates and the technical staff, as well as a little luck.
14th July – Dispatch from Chivay, Peru
After a busy few weeks in the Cordillera Carabaya, we’ve said goodbye to the snowy, tempestuous climate of the eastern Andes and are moving west to the desert of Arequipa. Here the mountains are massive, isolated volcanoes, many of which exceed 6000 m in elevation. In fact, Coropuna is the third highest mountain in Peru and certainly the most sprawling. It’s a landscape dominated by lava and aridity, and populated only by wild vicuna, condors, and a few hardy llama herders. Our first stop was Chivay, a lovely little town nestled in the upper Colca Canyon under the shadow of the enormous Nevado Ampato. We spent a day there recharging, replenishing our stocks and generally avoiding the blizzard on the plateau above. This being the desert, we had not anticipated that the bad weather would follow us west, but evidently it is possible. There is nothing quite like driving through the night, down the side of a canyon, in a snowstorm to focus the mind!
Our work here involves mapping both the glacial deposits and Holocene lavas on the two volcanoes, Ampato and Sabancaya. Though in sight of Arequipa, the place is actually more remote than Coropuna, accessible only via a two-hour drive down a washed out dirt road. This is a new region for us and so it promises to be a fascinating few days of exploring.
On July 11, we marked the successful completion of the first phase of our project and embarked on the second. Part 1 involved deploying ocean bottom seismometers and recording air-gun-generated sound waves. We successfully retrieved all of the OBS’s, and the data that they recorded look very exciting at first blush (and contain some surprises!). Part 2 involves towing two 8-km-long cables (or streamers) filled with pressure sensors behind the R/V Langseth, which will also record sound waves from the Langseth’s airgun array. Changing gears in terms of scientific activities also involved changes to our science party; we swapped personnel in Sand Point on a beautiful sunny evening. The excellent OBS team from Scripps departed on the Langseth‘s zodiak, and we were joined by new reinforcements. The newcomers included five undergraduate students from Columbia University, who are also blogging about their experiences at sea.
Just two hours after taking on our new personnel, we started deploying seismic gear – a very quick transition! Our seismic streamers are stored on gigantic spools, which unreel cable off the back of the ship into the ocean. A large buoy is affixed to the end of the streamer, and ‘birds’ are attached along its length, which can be used to control the depth of the streamer. Large paravanes hold the streamers apart; these are like large kites flying in the water off the back corners of the ship.
Deploying miles of streamer and the other attending gear is an impressively long and complicated undertaking. We started over two days ago, and have been working around the clock in shifts ever since. Many repairs and adjustments are made to the gear as it’s deployed. The streamer is divided into 150-m-long sections connected by modules; both sections and modules can fail and need to be replaced. Replacing a 150-m-long section of cable is an arduous task involving major manual labor by teams of ~5-6 people. But we are nearing the finish line; as I write, the last kilometer of the second streamer is going over the back of the boat. Fingers crossed that the deployment will soon be complete and the data collecting can begin!
10th July – Dispatch from Nevado Tolqueri, Cordillera Carabaya, Andes
We have acquired a dog, ¨”Mooch”. Walking back to camp yesterday, amid driving snow and fully laden with rock samples, there he was exploring what passes for our kitchen. Unlike most Andean dogs – ferocious beasts trained to keep geologists from harassing the livestock – this one is a cheerful soul, happy to hang around and be fed whatever is going, and always up for affection. Where he came from we don´t know. We´re camping at 4750 m in a shallow valley between moraines that keeps the worst of the wind at bay.
There is nothing to burn here and so the nights are frigid, though the view of the entire Cordillera Carabaya, as far as Bolivia, is superb. There are a few hardy souls farming alpacas up here, so presumably the canine comes from one of those, but nobody seems to be missing him. Last night he cleaned our plates and pans, as the snow fell all around, and this morning he was still there. I awoke to find Mooch curled up by the stoves, tucked up in a snowy ball. He immediately perked up once I arrived and waited with agreeable patience as we made a sort of rice pudding for breakfast. Then, with breakfast done, he followed Matt and me as we went off to collect a few more samples for surface-exposure dating. It will be sad to leave the pup, but we must head west soon to the desert Andes. And as Kurt noted, a high-altitude dog accustomed to sleep in the snow would hardly fare well in subtropical New York!
A word on the weather here. It´s taken a turn for the worse. We´ve been working on LGM moraines beneath Nevado Tolqueri and have made great strides there, collecting tens of samples from a fantastic sequence of moraines. But a drawn out storm has engulfed us from the east, appearing first as enormous thunder clouds and transitioning into incessant snow and high wind. It´s not quite what we´d expected but what can you do? It´s times like these we wish we had a kitchen tent instead of a patch of open mountain for cooking. It will be interesting to see how far west this system goes. In the meantime, we will try to keep our feet dry and the dog fed.