A new study in the journal Nature provides fresh insight into deep-earth processes driving apart huge sections of the earth’s crust. The process, called rifting, mostly takes place on seabeds, but can be seen in a few places on land—nowhere more visibly than in the Afar region of northern Ethiopia. (See the slideshow below.) Here, earthquakes and volcanoes have rent the surface over some 30 million years, forming part of Africa’s Great Rift Valley. What causes this, and does it resemble the processes on the seafloor, as many geologists think?
The study suggests that conventional ideas may be wrong. Past calculations done by scientists predict that the solid rock under the Afar should be stretching and thinning substantially as the continent tears apart; thus molten rock should not have far to travel to the surface. Led by David Ferguson, a postdoctoral researcher at Columbia University’s Lamont-Doherty Earth Observatory, researchers analyzed the chemical makeup of lava chunks they collected from the Afar. They showed that magmas actually came from quite deep–greater than 80 kilometers, or 45 miles, within the earth’s mantle–and formed under extraordinarily high temperatures, above 1,450 degrees C, or 2,600 F.
This implies that magmas are generated by a long-lasting plume of mantle heat. It also indicates that magma must make its way up through a surprisingly thick lid of solid rock, called the lithosphere. This idea has been supported by some seismic images of the Afar subsurface.
Rifting here is fairly slow—one or two centimeters a year, or 0.4 to 0.8 inches, and this may partly explain why so much solid rock persists. As the lithosphere is pulled apart, it does stretch, crack and thin. However, because the process in this region takes so long, the base of the lithosphere has time to cool down by losing heat to the colder rock above. This keeps the relatively cold, brittle lithosphere thicker than would be expected, and counteracts stretching. Sometimes, though, magma suddenly spurts long distances to the surface, and the earth visibly cracks and pulls apart during spectacular rifting events. That includes a series of events that started in 2005, and was closely observed by scientists.
Parts of the rift have already sunk below sea level. In the distant future–maybe 10 million years from now–the process will advance so far that the Red Sea will break through and flood the region. A new sea will open up, whether or not there is anyone around to name it.
In East Africa, earth’s crust is stretching and cracking, in a process called rifting. Here in the Afar region of northern Ethiopia, hundreds of faults and fissures have formed over time. (David Ferguson)
An important force driving the rifting is magma created beneath earth’s rocky outer shell, which has forced its way upward to push apart the crust. This eruption happened in the Afar in June 2009. (David Ferguson)
This crevice opened in a matter of hours, during a sequence of very large earthquakes in September 2005. It formed in response to magma being injected into the shallow crust, and is still emitting volcanic gases. This injection of magma was the largest event of its kind to be observed by scientists. (Lorraine Field)
Fresh lava erupted onto the desert floor preserves fragile surface textures, formed as the viscous molten rock cooled and hardened. Over time, these sharp features will erode away. (David Pyle)
A remote field site within the rift. Afar is one of the hottest and most sparsely populated regions on the planet. (David Pyle)
In a region that is vast, largely roadless and dominated by armed tribes, scientists depend on helicopters to get around, and on local people to act as guides and security guards. The climate necessitates large amounts of portable drinking water. (David Ferguson)
Lavas forming the rift surface cracked apart during an earthquake in 2005 to form this fault. The horizontal boundary between the light and dark area marks the pre-2005 ground surface, and shows that the area in the foreground dropped several meters during the quake. The geology of Afar provides many clues to the tectonic and magmatic process operating beneath our feet. (David Pyle)
June 22 was officially hump day – we were halfway through our 43-day cruise. Happily, we were also about halfway through our data collection; we had just finished acquiring the primary lines in the southern part of our survey area, which was a major milestone. The data are looking very nice (stay tuned for an upcoming post with some of the first images of features below the seafloor here from our new data!). Now that we have been out for a while and the survey was proceeding smoothly, everyone had settled into their shifts and routines, and the science party was consumed with onboard processing and archival of the incoming data stream. Funny enough, hump day and the near completion of half of our survey almost coincided with the summer solstice and a very full moon! It seemed like the convergence of many lucky omens.
Alas, it was not so. In the wee hours of the morning on June 24, the port engine failed as we were steaming along collecting data. The ship has two engines (partially in case of just such an event!). Fixing things at sea is obviously more complicated than fixing them on land, and the engineers onboard determined that the damage was significant and not quickly repaired. While we have the parts onboard to replace most of the known broken pieces, making the repairs and assessing the full extent of the damage is best done dockside. Thus we decided to pick up all our seismic gear and head back to Vigo to make the repairs. It took us >3 days to deploy all of the streamers, paravanes, and associated kit, but only about 12 hours to recover them! Now we are limping back to Vigo through relatively rough (3-4 m) seas powered by one engine. Once the damage and remedies for the port engine can be fully assessed, we can figure out our next move. Wish us luck!
All of us on the science team have had our turn being indoctrinated in the "perils" of XBT deployment. In this video, Luke demonstrates the proper technique for launching an XBT.
Prior to boarding the Langseth, my expectations of the food on board were clouded with visions of elementary school cafeteria slop doled out in aluminum trays and eaten with sporks and a side of plastic bag infused with milk. Little did I know that the folks on board take their food quite seriously. The three meals prepared each day are easily the most anticipated events of a crews’ day.
The galley (a.k.a. the kitchen in land dweller speak) is manned by a cook and steward who are responsible for sustaining the morale for the 53 people on board. The mess is regularly stocked with snacks like crackers, raisins, peanuts, dried prunes (yuck!), popcorn, cold cereal, microwave pasta, deli meats and cheeses, an assortment of milks and juices, coffee, tea, ice cream, and “fresh” fruits and vegetables (which will slowly be replaced with canned fruits and vegetables as the days go by). Cookies and pastries are also available at select times during the day if one is lucky enough to get there before they’ve all been consumed.
Between snacking times are the three glorious meals. Breakfast has the most stable menu of all the meals with a selection of eggs, potatoes, hot cereal, pancakes, French toast, bacon, sausage, ham, and a fruit platter that is now transitioning from fresh to canned fruits. Lunch generally consists of a type of sandwich, soup, French fries and/or onion rings, hot vegetables, rice, and other unpredictable delights. Supper has been quite intriguing as of late. We’ve been blessed with several kinds of steak, beef tenderloin, meatloaf, spaghetti, and many other varieties of taste bud tantalizing foods. For those who sleep during dinner and require a stomach recharge at 3am (yours truly and a good number of the crew on the midnight to noon shift), the galley staff save plates of dinner for “breakfast” that can be eaten during off times – I like to call this meal “brupper”, but am having difficulty getting the name to stick.
Lunch at the mess with Luke, Sarah, and Tyler.It has been entertaining to watch our young British colleagues become exposed to American cuisine for the first time with foods like peanut butter and jelly sandwiches, meatloaf (although they’ve been informed that it’s never as good as my mom’s – love you mom!), French toast, sausage in patty form, and Hershey’s chocolate syrup. It is also quite obvious that a 2,000 mile pond provides for the generation of different mealtime habits. For example, Luke was quite disgusted that I would dip a chocolate-chip cookie in a cold glass of milk; I shared his disgust when he spiced his French toast (sans-syrup) with salt and pepper and ate it like a normal piece of toast (apparently this was his first French toast experience). I’m guessing there will be some sort of payback if we ever meet in England sometime.
Well folks, speaking of the devil, I’m off to the mess for a warm breakfast. I hope you enjoyed the tour and stay tuned for the next one!
We made it! According to the 30 minute log, which is one of the duties that we are given while on watch, we sustained up to 40 knot (74 km/hr, 46 mph) winds and ~7m (23 ft) seas for a few hours last night. That said, and aside from a relative lack of sleep, most of us seem to be no worse for wear. We also managed to travel north of our next sail line by almost an entire degree of latitude, which translates to ~111km (69 miles). We have now turned around, and are heading back to the survey area while working on streamer one. We will then re-deploy the air guns, and re-engage the survey in a couple of hours.
Same view taken this morning.
Spanish, English, and American motion sickness remedies. We are also securing (tying down) our stuff and preparing our beds, which includes a new to us method coined "tacoing." To "taco" a bed means to use whatever you can find e.g. dirty clothes, luggage, random foam (Luke found some foam in the bird lab) in order to form a taco shape between your mattress and the wall. This way the roll has less of an affect on you as you try to get some sleep.. At least that's the theory.
My laptop's ready!Brian in a reasonably "taco'd" bed... And Luke's version.
Will update from the other side of the storm.
Wish us luck!Donna Shillington17th June Map of forecast wave heights posted in the main lab. The big bulls-eye is right over our field area...
We have been at sea for nearly two weeks, and during this time we have seen many things… the hints of exciting geologic structures under the seafloor in our data, waves, whales, gear going off the stern. But we have seen very little of the sun, until today. Most days have been overcast and grey. Now that all the equipment is deployed, there is nothing requiring us to be outside except for the occasional XBT launch, so it’s easy for a day or two to go by without going outside at all. It is even possible to be totally unaware of the weather for long stretches of time since the main lab, where we spend most of our time, is windowless and below the water line. Instead of windows, we have monitors showing what is happening out on various decks from a series of cameras around the ship. Today they showed bright sunshine reflecting off the water behind the ship. After spending a few minutes out in the sun on the deck, my unaccustomed eyes are still seeing spots…. Back to the lab!Bern and James are on watch, so they can only watch the sun on TV from the lab. Donna Shillington13th June
But no sooner had one problem been solved, another appeared. This time the trouble arose from the failure of a piece of equipment on the ship that is at the heart of our acquisition system – the real time navigation unit (or RTNU, for those in the know). This component gathers satellite and other navigational information from the seismic equipment and delivers it to the navigation software on the ship so that we can determine the positions of all of our equipment in the water, and where and when we need to be shooting. Once again, the dedicated technical staff of the Langseth came to the rescue. Painstaking checking and double-checking of each component in the RTNU began last night and continued into the early hours of the morning. In the wee hours, it’s easy to get a little superstitious. Did all these problems arise because Tim Reston and I each accidentally drew in lines on our chart indicating that we’d completed lines in our 3D box before we actually had? Or was it the curse of Costa da Morte (Coast of Death)? This part of the Galician coast is known for its shipwrecks and nicknamed accordingly. Of course, the real culprit was the non-newness of the gear in question. Once again, the Langseth’s miracle workers saved the day by assembling the working parts of various old RTNU’s into one working unit. Thanks to their efforts, we are up and running again….
RTNU carnage on a table in the main lab.
Poseidon's Zodiak on the way over to exchange supplies.
A few years ago, it was realised that seismic provides a method of directly observing the mixing processes, as the different water layers have sufficiently different seismic velocity and salinity for reflections to be generated at their boundaries: we have already seen reflections in the water column of our data, probably from boundaries between North Atlantic water and warmer, more saline Mediterranean water. However there have been relatively few studies of these processes using traditional oceanographic and seismic techniques, a deficiency being rectified by the deployment of XBTs at regular intervals during our cruise.
A successful exchange on medium-high seas!!
In addition to deploying ocean bottom seismometers to record our seismic shots, the German research vessel F.S. Poseidon has been carrying out oceanographic measurements, mainly using CTD casts (conductivity-temperature-depth), which provide more information than XBTs. As a result they had several XBTs left over. These they transferred to us this morning: Poseidon came within about 1 km of the Langseth and sent the XBTs over in a small boat. A real bumpy ride!
Goodbye, until we meet in Vigo!Tim Reston
University of Birmingham
After days of uneventful and productive data acquisition, a pale fell over the R/V Langseth. Early Sunday morning, one of the streamers began to report communication errors and soon failed to communicate at all. A series of tests over the ensuing hours revealed that the problem was not on the ship but in the equipment out in the water. Recovering and repairing seismic gear is not a quick task. To access this streamer, we had to undo many of the steps required to put it out to begin with: recover the port paravane, shift Streamer 3 starboard and out of the way, and then reel in part of Streamer 4. After hours of troubleshooting, the technical staff of the Langseth brought Streamer 4 back to life. All of the equipment on the Langseth is… not new, and this certainly applies to the seismic streamers. The technical staff on the ship are pros at keeping this equipment alive (and many cases bringing it back from the dead). Twelve hours after the problems with Streamer 4 began, it was back in the water, and we were ready to start collecting data again. But no sooner had one problem been solved, another appeared. This time the trouble arose from the failure of a piece of equipment on the ship that is at the heart of our acquisition system – the real time navigation unit (or RTNU, for those in the know). This component gathers satellite and other navigational information from the seismic equipment and delivers it to the navigation software on the ship so that we can determine the positions of all of our equipment in the water, and where and when we need to be shooting. Once again, the dedicated technical staff of the Langsethcame to the rescue. Painstaking checking and double-checking of each component in the RTNU began last night and continued into the early hours of the morning. In the wee hours, it’s easy to get a little superstitious. Did all these problems arise because Tim Reston and I each accidentally drew in lines on our chart indicating that we’d completed lines in our 3D box before we actually had? Or was it the curse of Costa de Morte (Coast of Death)? This part of the Galician coast is known for its shipwrecks and nicknamed accordingly. Of course, the real culprit was the non-newness of the gear in question. Once again, the Langseth’s miracle workers saved the day by assembling the working parts of various old RTNU’s into one working unit. Thanks to their efforts, we are up and running again….
RTNU carnage on a table in the main labDonna Shillington10th June
Today the Poseidon is recovering eight OBH to download the data they recorded and redeploy them elsewhere within the 3-D box. It will be exciting to see the first OBH data! We won't see the rest of the data until the remaining OBS and OBH are recovered in August and September.
Despite being in the same area, here on the Langseth the science party hasn't seen the Poseidon since our first day passing them on the way out to sea from Vigo. However, this may be because we are all busy below deck in the main lab (with no windows) processing data!
Donna Shillington8th June
Map in the main lab showing planned profiles. The ones we've already completed are in green
*Follow our progress on the "Survey Area" page as we update the sail lines every ~4 days.
Marine reflection seismology involves actively generating soundwaves (rather than waiting for earthquakes as in many other types of seismology). The ideal seismic source is as close to a “spike” as possible. Sound waves from the source travel into the Earth, where they reflect off sedimentary layers as well as hard-rock surfaces. The returning reflections are recorded by over a thousand hydrophones (underwater microphones that gauge pressure changes created by the reflected seismic waves) in the streamers that we have been deploying for the last four days.
The source consists of a series of air guns of varying sizes, which are hung at a depth of 9m (~30 feet) below large inflatable tubes. The tubes are 60m (~200 feet) long and each has 9 active air guns (10 with one to spare). In our case there are two sets of air guns being towed 150m (~500 feet) behind the ship, that alternately fire. To create a strong source that is as spike-like as possible, the guns are carefully arranged and fire almost simultaneously. The air is released from the chamber of the air gun, creating a 3300 cubic inch bubble pulse, which collapses to create the sound waves.
Orientation of the streamer and gun arrays being towed by R/V Langseth.
The red circles indicate the location of the gun arrays.We are making sound in the ocean, where many mammals use sound to communicate and hunt for food. In order to ensure we are operating responsibly and minimizing our impact on mammals, we have five Protected Species Observers (PSO’s) onboard who both watch and listen for (from the observation deck in Donna’s previous post) any marine mammal that comes close to the ship. If any are spotted or heard within a specified radius around the ship, we power down the guns until they leave the area.
The second paravane went in the water at 22:00 this evening, and streamer 2 is currently being uncoiled into the water behind the ship. Despite a few delays, we are making good progress!
Marianne Karplus4th June
Most of the science group has been working in 4 hour shifts thus far - 4 hours of work and then 8 hours of time for other things each 12 hour period. The last day or two, I was using my 8 hour rest periods to eat a couple of saltines, lie down, and attempt to ignore the rocking of the ship, but I must be getting used to the seas (and they are calmer!) because I can now do other things like read papers and look at a computer screen.
We have been collecting data almost since we left port. We are mapping the bathymetry, collecting gravity data, recording ocean current directions, etc. Since we entered our 3-D box area yesterday, it's been exciting to identify fault scarps in the bathymetry.
Donna mentioned in her previous post that once a streamer is in the water, its location is monitored and it can be moved around using winged devices called "birds" that are attached to it. Imagine a number of actual birds holding a cable in their talons at an even spacing while flying. Our mechanical birds are not so different, except they are flying the streamer through the water. We can see where the birds are on a computer screen in the lab, and we can control the depths of the birds by remotely moving their wings. When a streamer goes into the water, it can take some time to get the weighting right and then for the birds to dive the streamer down to the desired depth (generally 8-12 meters below the sea surface).
3rd June (posted late due to internet outage)
Assembing a bird to be attached to the streamer.Birds for streamers 2 and 3 waiting to be deployed.
After steaming for twelve hours out of port, we started the long process of putting out all of the seismic gear needed for this program. The weather worsened as we headed towards the field area, and we have been deploying equipment in 3-4 meter swells for the last 18 hours. This ship can roll by up to 10-15 degrees in these conditions (and more than a couple of people are feeling sea sick as a result). On the deck, ropes and cables connected to equipment towed off the back of the ship lurch and clank rhythmically, and water commonly washes over the lower deck. Down in the main lab, stray items that aren’t properly stowed or strapped down start to roll back and forth, the ship creaks and groans, and office chairs swivel with each swell.
For this program, we will be towing an enormous amount of gear behind the ship to enable us to image faults involved in rifting, the exposure of mantle rocks and continental breakup in 3D. Four 6-km-long seismic ‘streamers’ filled with pressure sensors (which can detect returning sound waves) will be towed 200 m apart, for a full spread of 600 meters. As we deploy the streamers, we add weights to ballast the streamer, acoustic units to determine the locations of the streamers, and ‘birds’ that enable us to control the depth of the streamer remotely. We also swap out broken pieces. The streamers are held apart by two gigantic paravanes, which are like large metal kites that fly out from either side of the ship. Each one weighs an astonishing 7.2 tons and is ~7.5x6 meters in size. There are also myriad floats, cables and ropes to maintain the correct geometry of the entire array. The streamers will record returning sound waves generated by two arrays of air guns, which will be towed 100 m apart and fired separately. We expect that it will take us 3 days to deploy this complicated array of equipment behind the ship. The weather is expected to start improving tomorrow afternoon, which will help us greatly!
2nd June Looking forward on the Langseth as she takes a roll in the swell.A streamer with a 'bird' being deployed off the Langseth's stern into the waves.
The R/V Marcus G. Langseth pushed away from the docks of Vigo at 8 am local time. The sun was shining, and the views of the rugged cliffs, forests and Galician towns along the coastline were spectacular. We will only be able to see land at the very beginning and very end of this 45-day cruise. We steamed out of the protected waters around Vigo and out into the open Atlantic Ocean a few hours later, and happily were met by relatively calm seas (1-2 meter swells), although its quite brisk compared to summer weather back home. We actually saw the F.S. Poseidon in the distance as she headed back to Vigo at the end of the first OBS cruise of this program. We only have a relatively short transit of ~10 hours before we begin to deploy the extensive suite of scientific equipment behind the ship needed to image the structures beneath the seafloor in 3D. Putting out the seismic streamers and associated gear will take 3 days!
1st June The science party on deck as the ship departs Vigo.
I returned to New York on Monday, but Lamont-Doherty Earth Observatory scientists Andy Juhl and Craig Aumack remain working in Barrow, Alaska for another week. They’ll continue to collect data and samples in a race against deteriorating Arctic sea ice conditions as the onset of summer causes the ice to thin and break up. Even in the two weeks I stayed in Barrow the ice changed dramatically, shifting from a snow-covered ice pack to a nearly snow-free ice pack, covered in cracks and increasingly large melt ponds. An animation from the May 23 Barrow sea ice radar reveals just how quickly shorefast sea ice can change. Soon the ice will be deemed unsafe for travel by snow machine and spring fieldwork conducted on the ice will end.
Our team’s research in Barrow is just one part in the long process of studying and answering questions about algae growing in and under Arctic sea ice and its role in the marine ecosystem. And, it’s a process that does not necessarily have a defined end — investigating the natural world always leads to more questions. From fieldwork, where observations are made and data gathered, new questions arise, new hypotheses are put forward and new ways of collecting data are developed. This work leads to further experiments where new data and samples are collected, observations are made, analyses performed and results interpreted. Some of the findings will challenge existing hypotheses, leading to their modification, which starts the research process over again.
Fieldwork gives scientists the opportunity to observe systems in a holistic way, leading to new insight and further research questions; each piece of data causes a rethinking of ideas and expectations for future results. “Fieldwork is inspiring and it’s critical to the creative process for environmental science because you often see things that you don’t necessarily see in your data,” said Andy. “There are subtleties and patterns that you can pick on if you pay attention to observe the natural world. You can’t do that in the lab or by looking at numbers.”
Some people may be disappointed to learn that we don’t have many immediate answers about sea ice algae and the Arctic ecosystem based on our month of Barrow fieldwork. But, scientists don’t set out to study things that are already understood or to answer questions that already have answers, and it takes time to unravel Earth’s mysteries. On this trip, project scientists discovered and collected lots of algae, observed novel behavior by marine organisms in the water column and on the seafloor, and gathered lots of data. The next steps in this project are to analyze the samples and data collected in Barrow, interpret these, write up findings and report these in journals and at scientific meetings. And, in 2014, Andy and Craig will return to Barrow to continue their study of sea ice algae, armed with new understanding of the algae, as well as new research questions to explore.
The goal of our project is to understand how ice algae functions and its role in the marine ecosystem, but we’ve received many questions about how ice algae, the residents of Barrow and the rest of life in the Arctic will be affected by a climate that is undoubtedly and irrevocably changing. The answer is that we don’t know, but our research may contribute to future understanding of these issues. Though the Arctic is changing faster than anywhere else on the planet, with temperature increasing and ice volume decreasing, it is still one of the least explored places on Earth. In order to know how climate change will impact this region, the basic oceanographic and ecological processes must first be understood.
As our project progresses, we’ll continue to provide updates and look forward to sharing a video of our time in Barrow that’s being produced by our friends at Climate Science TV. For more information on this research project, visit http://lifeintheice.wordpress.com. Our colleagues at Lamont-Doherty Earth Observatory also travel the world exploring our planet; to keep up with more interesting Earth science research and reports from the field, follow Lamont-Doherty on Twitter and Facebook.
And thanks to everyone who followed our expedition, we enjoyed sharing it with you!
Today they are reloading the ship with 18 more OBS to deploy on Leg 2. The personnel on board will also exchange two Ocean Bottom Instrument Consortium personnel for two GEOMAR personnel.
What is an OBS?
An OBS is an autonomous instrument that sits on the ocean floor and records waves (sound waves as well as other types) traveling through the earth and/or ocean water. All of our Galicia instruments have ocean bottom hydrophones (OBH) to record waves traveling through the ocean (including some types of whale calls!), and a subset of fifty also have geophones to record waves traveling through the sediments and rocks beneath the sea floor.
The OBS record waves by measuring tiny motions of the earth and sea water, converting it into electrical signals, which are stored digitally. The geophones, data logger, and batteries are stored in a water tight, floating sphere, and the hydrophone is attached to the outside of the sphere. A heavy anchor attached to the sphere enables it to sink to the bottom when it is deployed (sent off into the ocean).
To pick up the OBS, the ship goes to the location where it was deployed, and a sound signal with a particular frequency is sent out. The OBS replies acoustically, cuts its anchor, and resurfaces. Scientists can then download the data and begin to piece together a picture of the local Earth structure!