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<title>Naomi Barshi – JOIDES Resolution</title>
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<link>https://joidesresolution.org</link>
<description>Science in Search of Earth's Secrets</description>
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<title>Naomi Barshi – JOIDES Resolution</title>
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<item>
<title>Incoming! Oblique Subduction at the Sunda Subduction Zone</title>
<link>https://joidesresolution.org/incoming-oblique-subduction-at-the-sunda-subduction-zone/?utm_source=rss&utm_medium=rss&utm_campaign=incoming-oblique-subduction-at-the-sunda-subduction-zone</link>
<comments>https://joidesresolution.org/incoming-oblique-subduction-at-the-sunda-subduction-zone/#respond</comments>
<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Sun, 25 Sep 2016 20:05:30 +0000</pubDate>
<category><![CDATA[earthquakes_659]]></category>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[Expedition 362 Sumatra Seismogenic Zone]]></category>
<category><![CDATA[Plate-Tectonics]]></category>
<category><![CDATA[strike-slip fault]]></category>
<category><![CDATA[Subduction]]></category>
<category><![CDATA[subduction zone]]></category>
<category><![CDATA[subduction zones]]></category>
<category><![CDATA[tectonics]]></category>
<guid isPermaLink="false">https://joidesresolution.org//incoming-oblique-subduction-at-the-sunda-subduction-zone</guid>
<description><![CDATA[The Indian and Australian Plates plow northeast into the Sumatra subduction zone, part of the larger Sunda subduction zone, at a... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/incoming-oblique-subduction-at-the-sunda-subduction-zone/" title="Continue reading Incoming! Oblique Subduction at the Sunda Subduction Zone">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p class="p1">The Indian and Australian Plates plow northeast into the Sumatra subduction zone, part of the larger Sunda subduction zone, at a speed of 45 mm/yr. The angle between the direction these two plates move relative to each other is not always at a right angle (90°) to the subduction zone itself–here it is about 50°. Sliding under the Sunda Plate at an angle is not easy, so several large strike-slip fault systems help to accommodate some of this movement. If you thought learning vectors in high school was pointless—think again. This is a perfect vector component problem!</p>
<p>Before we get to big words about big faults, let’s review vectors. If you want to walk from one corner of an intersection to the corner diagonally across from you, you typically go along one side of the intersection, wait for the pedestrian light, and then walk the other side. You’ve walked two sides of a triangle to get to your destination. The third side of the triangle is the line that connects your start and end points:</p>
<p><img fetchpriority="high" decoding="async" class="alignnone size-full wp-image-23600" src="https://joidesresolution.org//wp-content/uploads/2016/09/roadCross.png" alt="" width="306" height="244" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/roadCross.png 306w, https://joidesresolution.org/wp-content/uploads/2016/09/roadCross-300x239.png 300w" sizes="(max-width: 306px) 100vw, 306px" /></p>
<p> </p>
<p class="p1">Each side of the triangle is a vector, and we can think of the two pedestrian crossings as components (purple lines/arrows) of the vector that connects your start and end points (orange line/arrow). A vector is a quantity that has a magnitude (in this case length, the distance across the intersection = 20m) and a direction (NW). Any vector can be broken down into component lengths and directions at right angles, like the two sides of the intersection that you just walked.</p>
<p class="p1">The motion of the Indian Plate coming into the North Sumatran subduction zone is also a vector. We can break it down into two components: one parallel to the subduction zone (yellow arrow on map below) and one perpendicular to the subduction zone (orange red arrow). Because the Indian/Australian plate comes in at an angle other than 90º to the subduction zone, we call it “oblique subduction”. (Plate motion vectors and fault locations adapted from Meltzner et al., 2012.)</p>
<p><img decoding="async" class="alignnone size-full wp-image-23602" src="https://joidesresolution.org//wp-content/uploads/2016/09/subductvectors.jpg" alt="" width="640" height="462" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/subductvectors.jpg 640w, https://joidesresolution.org/wp-content/uploads/2016/09/subductvectors-300x217.jpg 300w" sizes="(max-width: 640px) 100vw, 640px" /></p>
<p>The main subduction zone thrust fault takes up primarily the NE-directed motion of the Indian Plate, perpendicular to the subduction zone. That is, the orange red component of the plate motion vector is taken up by earthquakes on the subduction zone that allow the plates to move past each other. Here are two models that show the motion of the plates during the 2004 M 9.2 Great Sumatra-Andaman Islands Earthquake. During the earthquake the plate overlying the subduction zone actually rebounded towards the SW, over the down-going Indian Plate. Notice that the arrows (from GPS measurements of ground motion change before and after the earthquake) point almost directly across the subduction zone at 90º (models from Chlieh et al., 2007, and Rhie et al., 2007).</p>
<p><img decoding="async" class="alignnone size-full wp-image-23601" src="https://joidesresolution.org//wp-content/uploads/2016/09/RuptureGPS.jpg" alt="" width="640" height="599" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/RuptureGPS.jpg 640w, https://joidesresolution.org/wp-content/uploads/2016/09/RuptureGPS-300x281.jpg 300w" sizes="(max-width: 640px) 100vw, 640px" /></p>
<p class="p2">But there is still plate motion to account for in the system: the yellow component of the overall plate motion. Faults parallel to the subduction zone take up the slack – This is fairly common in subduction zones because plates rarely meet exactly head on. These long, subduction zone-parallel faults are strike-slip faults. They’re nearly vertical in the subsurface, and motion along them can be seen looking straight down, as if looking at a map. The San Andreas Fault is a well-known example of a strike-slip fault that lets the Pacific Plate move north along the North American Plate. In Sumatra, the primary fault taking up this motion is the Great Sumatran Fault which runs along the center of the island of Sumatra. In fact, the fault runs very close to the volcanic arc of the subduction zone. The southwestern side of the fault moves to the northwest, the same direction as the plate motion not accounted for by subduction. There are also other strike-slip faults offshore, also parallel to the subduction zone, which help to take up some of this plate motion. This figure shows different historic and recent earthquakes in the Sumatra region, including along the Great Sumatran Fault, parallel to the Sunda Trench (Fig. 10 in McCaffrey, 2009).</p>
<p> </p>
<p><img loading="lazy" decoding="async" class="alignnone size-full wp-image-23598" src="https://joidesresolution.org//wp-content/uploads/2016/09/McCaffrey_SumatraFig.jpg" alt="" width="640" height="276" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/McCaffrey_SumatraFig.jpg 640w, https://joidesresolution.org/wp-content/uploads/2016/09/McCaffrey_SumatraFig-300x129.jpg 300w" sizes="auto, (max-width: 640px) 100vw, 640px" /></p>
<p> </p>
<p class="p2">The Great Sumatran Fault carries its own seismic hazard that adds to the risk posed by subduction zone earthquakes and tsunami. On top of the seismic hazard, the southwestern and southern coast of Sumatra and Java host many active volcanoes. The volcanoes are also part of the subduction zone system: they are fed by molten material from the mantle because of the ocean crust subducting below. (That’s another post for another time!)</p>
<p class="p2">Here’s a map of the seismic hazard of Indonesia and Malaysia that shows the maximum amount the ground is likely to move during earthquake shaking in the next 50 years. “How much” is expressed as peak ground acceleration, in percent of the normal acceleration caused by gravity. “Likely” is a 10% chance that the ground will move that much during the 50 year time period. (Map created by the USGS based on data from a variety of sources. See Further Reading for full map poster with citations.)</p>
<p> </p>
<p><img loading="lazy" decoding="async" class="alignnone size-full wp-image-23603" src="https://joidesresolution.org//wp-content/uploads/2016/09/SumSeismHazUSGS.jpg" alt="" width="640" height="565" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/SumSeismHazUSGS.jpg 640w, https://joidesresolution.org/wp-content/uploads/2016/09/SumSeismHazUSGS-300x265.jpg 300w" sizes="auto, (max-width: 640px) 100vw, 640px" /></p>
<p> </p>
<p class="p1">This type of plate boundary geometry is not unique to the Sumatra region. In many plate boundaries where plates converge at an angle rather moving straight toward each other, we see that long strike-slip fault systems help to take up the overall plate motion. The Liquine-Ofqui Fault and Atacama Fault serve a similar purpose in the Andean subduction zone in Chile. The Median Tectonic Line is the largest strike-slip fault in Japan and accounts for the oblique motion at the Nankai subduction zone. Learning about processes at one site on Earth can help us understand what’s going on elsewhere in the world!</p>
<p class="p1"><strong>Sources and Further Reading</strong></p>
<p class="p1"><u>General information</u></p>
<p class="p1"><u>Journal articles</u></p>
<p class="p1">Baroux et al., 1998. Slip-partitioning and fore-arc deformation at the Sunda Trench, Indonesia. Terra Nova, 10 (3), 139-144.</p>
<p class="p1">Bellier and Sébrier, 1995. Is the slip rate variation on the Great Sumatran Fault accommodated by fore-arc stretching? Geophysical Research Letters, 22 (15), 1969-1972.</p>
<p class="p1">Berglar et al., 2010. Structural evolution and strike-slip tectonics off north-western Sumatra. Tectonophysics 480, 119-132.</p>
<p class="p1">Chlieh, M., Avouac, J.-P., Hjorleifsdottir, V., Song, T.-R.A., Ji, C., Sieh, K., Sladen, A., Hebert, H., Prawirodirdjo, L., Bock, Y., and Galetzka, J., 2007. Coseismic slip and afterslip of the great (Mw 9.15) Sumatra-Andaman earthquake of 2004. Bulletin of the Seismological Society of America, 97(1A):S152–S173. <a href="http://dx.doi.org/10.1785/0120050631">http://dx.doi.org/10.1785/0120050631<</a></p>
<p class="p1">Fitch, T.J., 1972. Plate convergence, transcurrent faults, and internal deformation adjacent to Southeast Asia and the Western Pacific. Journal of Geophysical Research 77 (23), 4432–4460. <a href="http://onlinelibrary.wiley.com/doi/10.1029/JB077i023p04432/epdf" class="broken_link">doi:10.1029/JB077i023p04432<</a></p>
<p class="p1">McCaffrey, R., 2009. The Tectonic Framework of the Sumatran Subduction Zone, Annual Reviews in Earth and Planetary Sciences, 37, 345-366.</p>
<p class="p1">Meltzner, A. J., K. Sieh, H.-W. Chiang, C.-C. Shen, B. W. Suwargadi, D. H. Natawidjaja, B. Philibosian, and R. W. Briggs, 2012. Persistent termini of 2004- and 2005-like ruptures of the Sunda megathrust, Journal of Geophysical Research, 117, B04405,</p>
<p class="p1">Rhie, J., Dreger, D., Bürgmann, R., and Romanowicz, B., 2007. Slip of the 2004 Sumatra-Andaman earthquake from <dfn title="Look up the definition of Joint.">joint</dfn> inversion of long-period global seismic waveforms and GPS static offsets. Bulletin of the Seismological Society of America, 97(1A):S115–S127. <a href="http://dx.doi.org/10.1785/0120050620">http://dx.doi.org/10.1785/0120050620<</a></p>
<p> </p>
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]]></content:encoded>
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</item>
<item>
<title>The Earthquake that Triggered Expedition 362</title>
<link>https://joidesresolution.org/the-earthquake-that-triggered-expedition-362/?utm_source=rss&utm_medium=rss&utm_campaign=the-earthquake-that-triggered-expedition-362</link>
<comments>https://joidesresolution.org/the-earthquake-that-triggered-expedition-362/#respond</comments>
<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Wed, 21 Sep 2016 22:01:47 +0000</pubDate>
<category><![CDATA[earthquakes]]></category>
<category><![CDATA[earthquakes_659]]></category>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[Expedition 362 Sumatra Seismogenic Zone]]></category>
<category><![CDATA[Sumatra Seismogenic Zone]]></category>
<category><![CDATA[tsunami]]></category>
<guid isPermaLink="false">https://joidesresolution.org//the-earthquake-that-triggered-expedition-362</guid>
<description><![CDATA[In 2004, a magnitude 9.2 earthquake struck the northern Sumatra region and triggered a tsunami that inundated the Indian Ocean... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/the-earthquake-that-triggered-expedition-362/" title="Continue reading The Earthquake that Triggered Expedition 362">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p>In 2004, a magnitude 9.2 earthquake struck the northern Sumatra region and triggered a tsunami that inundated the Indian Ocean coast. The disaster was an important reminder to earth scientists that we must better understand the processes at work in subduction zones so that we can help mitigate future disasters. The earthquake was extremely powerful and surprising to geologists in that it was able to break through the plate boundary to relatively shallow depths (5-7 km) below the seafloor. This poster explains some of the details about the events of 26 December 2004, which spurred the scientists on board Expedition 362 to drill into the seafloor and study the rocks and sediments that host major earthquakes once they reach the subduction plate boundary.<br />
<!--break--></p>
<p> </p>
<p>For further reading, check out our pages about earthquakes and subduction zones, two of the main topics under study by <a href="https://joidesresolution.org//expedition/362/">Expedition 362: Sumatra Seismogenic Zone</a>.</p>
<p>This poster is printable on 11×17 in paper.</p>
<p> </p>
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</item>
<item>
<title>Daily Science Report Explained</title>
<link>https://joidesresolution.org/daily-science-report-explained/?utm_source=rss&utm_medium=rss&utm_campaign=daily-science-report-explained</link>
<comments>https://joidesresolution.org/daily-science-report-explained/#respond</comments>
<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Tue, 13 Sep 2016 17:44:18 +0000</pubDate>
<category><![CDATA[carbonate sediments]]></category>
<category><![CDATA[carbonate sediments core description]]></category>
<category><![CDATA[core description]]></category>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[Expedition 362 Sumatra Seismogenic Zone]]></category>
<category><![CDATA[sediment cores]]></category>
<category><![CDATA[sedimentary rocks]]></category>
<category><![CDATA[Structural Geology]]></category>
<category><![CDATA[Sumatra Seismogenic Zone sediment cores sedimentary rocks Structural Geology veins]]></category>
<category><![CDATA[veins]]></category>
<guid isPermaLink="false">https://joidesresolution.org//daily-science-report-explained</guid>
<description><![CDATA[Each day, our Staff Scientist/Expedition Project Manager sends out an update to the ship and to our colleagues on shore.... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/daily-science-report-explained/" title="Continue reading Daily Science Report Explained">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p>Each day, our Staff Scientist/Expedition Project Manager sends out an update to the ship and to our colleagues on shore. The daily report summarizes the scientific findings from the day before. Here’s an example of a daily report, explained with photos!<br />
<!--break--><br />
Click on the photo at left to make it bigger. </p>
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</item>
<item>
<title>From Mud to Rocks</title>
<link>https://joidesresolution.org/from-mud-to-rocks/?utm_source=rss&utm_medium=rss&utm_campaign=from-mud-to-rocks</link>
<comments>https://joidesresolution.org/from-mud-to-rocks/#respond</comments>
<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Sun, 11 Sep 2016 19:36:50 +0000</pubDate>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[Geology_482]]></category>
<category><![CDATA[sedimentary rocks]]></category>
<category><![CDATA[Sumatra Seismogenic Zone]]></category>
<guid isPermaLink="false">https://joidesresolution.org//from-mud-to-rocks</guid>
<description><![CDATA[Agnes just gave us a nice primer on mud. But what happens next to make mud into a rock? First, we... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/from-mud-to-rocks/" title="Continue reading From Mud to Rocks">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p class="p1">Agnes just gave us a nice primer on mud. But what happens next to make mud into a rock?</p>
<p class="p1"><strong>First, we need to answer the question, What’s a rock? </strong></p>
<p class="p1">This is a simple question, but it’s tricky to tie down a simple AND satisfying answer. Most of the geologists I asked on board said, “A rock is a solid aggregate of minerals.” That’s what a textbook says, but others disagree with the boundaries of this definition. What about coal? That’s not made of minerals. What about our bones? They’re not rocks.</p>
<p class="p1">“Making boxes is difficult in a messy world,” sedimentologist Kitty Miliken told me when I asked her about the definition of a rock. “If you’re going to be a scientist”, she said, you’ll want to make a lot of boxes. “But you need to be prepared for Nature not to respect your boxes.” So, according to Kitty, the boundaries of the box around “rock” are:<br />
– naturally occurring<br />
– hard<br />
– solid<br />
– that’s not easily disaggregated or broken apart<br />
– not just made by a single organism, though it may contain parts of organisms (fossils)<br />
– and is any combination of the following:<br />
– an aggregate of minerals and/or organic material<br />
– monocrystalline or polycrystalline<br />
– all of one composition or a mixture of different compositions.</p>
<p class="p1">This seems to work for our purposes of what’s rock and what’s not yet a rock. Note that some rocks do break apart easily. Shale by definition breaks into sheet-like layers. But it’s still a coherent mass of mineral grains that doesn’t just fall apart in your hands.</p>
<p class="p2">The sediments we’re looking at are well on their way to fitting this definition: they’re naturally occurring, the individual grains or minerals or fossils are hard (though the combination of them is not yet hard), they’re individually solid, and they’re not made just by one organism. There are lots of different minerals, so in this case the rocks that our sediments will turn into are polycrystalline and a mixture of different compositions. Some rocks are made of just one mineral, like quartzite (quartz) or limestone (calcite).</p>
<p class="p1">When sediments settle to the seafloor, they form a layer of particles, whether they’re grains of sand, silt, and clay from land or tiny micro-organisms that lived in the ocean. Sediments are already made of the right stuff, but they might not yet be rocks. The young sediments in the upper kilometer or so of seafloor that we drilled through were not yet rocks. For the first few hundred meters of the holes at Site U1480, the sediments were soft and easily disaggregated. That is, we could easily take a tiny toothpick scoop of sand or mud and smear it around on a smear slide, as Agnes explained in a recent blog post.</p>
<p class="p1">What exactly the sediments are made of determines how quickly they’ll become a true rock. Carbonate minerals eventually make up rocks like limestone. They’re reactive and can quickly turn into rock. If you go to the beach in the Caribbean, where there are high concentrations of carbonate minerals in the seawater, you can see rocks forming over a time period of years. It can take millions or even tens of millions of years for sand and mud to turn to rock. This process of becoming a rock can be sped up if there’s carbonate-rich water flowing between the grains of sand and mud or carbonate grains (shell fragments, calcareous algae flakes, etc.). The calcium, carbon, oxygen, and other atoms that make up carbonate minerals dissolved in the water can then grow together as carbonate minerals between grains of sediment and glue them together. This is called <strong>cementation</strong>. Carbonate minerals can also glue non-carbonate chunks together. We found a layer of proper sandstone in one of our cores, with carbonate minerals cementing the sand grains together.</p>
<p> </p>
<p><img loading="lazy" decoding="async" class="alignnone size-full wp-image-23606" src="https://joidesresolution.org//wp-content/uploads/2016/09/Figure-U1480-C-F36_sm.jpg" alt="" width="640" height="986" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/Figure-U1480-C-F36_sm.jpg 640w, https://joidesresolution.org/wp-content/uploads/2016/09/Figure-U1480-C-F36_sm-195x300.jpg 195w" sizes="auto, (max-width: 640px) 100vw, 640px" /></p>
<p> </p>
<p class="p1">The image shows a core section scan with close-up photos taken with a microscope, looking through a very thin slice of the rock glued to a glass slide.</p>
<p class="p1">There were layers of unconsolidated sand above and below that were not yet sandstone because the grains weren’t cemented together. We interpret that this rock layer must have been a place where underground water could flow because sand is very porous and permeable, meaning water can easily flow through it. The water was rich in carbonate ingredients, so carbonate minerals were able to glue the grains of sand together. Other kinds of cement are silica and iron oxide. The iconic red sandstones of the American Southwest owe their color to iron oxide cement. The grains of sand that comprise them are actually mostly colorless quartz!</p>
<p><img loading="lazy" decoding="async" class="alignnone size-full wp-image-23610" src="https://joidesresolution.org//wp-content/uploads/2016/09/UtahRocks.jpg" alt="" width="500" height="312" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/UtahRocks.jpg 500w, https://joidesresolution.org/wp-content/uploads/2016/09/UtahRocks-300x187.jpg 300w" sizes="auto, (max-width: 500px) 100vw, 500px" /></p>
<p> </p>
<p class="p1">Sandstones with iron oxide cement in Arches National Park, Utah. (Photo © Naomi Barshi)</p>
<p class="p1">In addition to cementation, <strong>compaction</strong> also helps turn loose sediments into rocks. As sediments get buried by more sediments and water above, they “feel” more and more pressure. Even just 4200 m of water, where we are now, provides 400 times as much pressure as the atmosphere exerts on us. At 1000 <dfn title="Look up the definition of Mbsf.">mbsf</dfn>, there’s an additional 200 times atmospheric pressure just from the overlying sediments. We could very clearly see the difference between young, uncompacted sediments at the top of the hole and much older (more than 60 million years older!) compacted sediments and true sedimentary rocks near the base of the hole. Here are some photos for comparison. The first is some silty, clayey land-derived sediment very characteristic of the mid-shallow subsurface of the ocean.</p>
<p><img loading="lazy" decoding="async" class="alignnone size-full wp-image-23609" src="https://joidesresolution.org//wp-content/uploads/2016/09/siltyClay.jpg" alt="" width="640" height="496" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/siltyClay.jpg 640w, https://joidesresolution.org/wp-content/uploads/2016/09/siltyClay-300x233.jpg 300w" sizes="auto, (max-width: 640px) 100vw, 640px" /></p>
<p><img loading="lazy" decoding="async" class="alignnone size-full wp-image-23608" src="https://joidesresolution.org//wp-content/uploads/2016/09/SedRocks.jpg" alt="" width="800" height="577" srcset="https://joidesresolution.org/wp-content/uploads/2016/09/SedRocks.jpg 800w, https://joidesresolution.org/wp-content/uploads/2016/09/SedRocks-300x216.jpg 300w, https://joidesresolution.org/wp-content/uploads/2016/09/SedRocks-768x554.jpg 768w" sizes="auto, (max-width: 800px) 100vw, 800px" /></p>
<p class="p1">Compaction by increased pressure, increasing temperature with depth, and the flow of fluids in the spaces between the rocks can also change the chemical composition of the sediments. Minerals can have many different elements inside their crystal lattice structures, including hydrogen and oxygen together as hydroxide. These can be squeezed or heated off. The oxygen and hydrogen they combine into to pure water plus a new, chemically dry mineral left behind. These kinds of mineral reactions are called “dehydration reactions” and are very important for the behavior of rocks and sediments, especially when they get hot and are put under pressure. Water weakens rocks and sediments, lets rocks melt at lower temperatures, and makes sediments more slippery. We can tell if these reactions are happening in the sediments by measuring the composition of interstitial water in the cores. We squeeze the water out of the sediments in the <dfn title="Look up the definition of Chemistry.">chemistry </dfn>lab (physically only—we don’t squeeze so hard that we cause chemical de-watering). We expect that the interstitial water should be seawater, so if we see freshwater, we know it’s from dehydration reactions. Water moving between the grains of sediments and rocks can also react with the minerals to form new, chemically wet minerals. This can cause changes in volume and has all sorts of implications for rock composition and strength. Lest I write a <dfn title="Look up the definition of Geology.">geology</dfn> textbook instead of a blog post, I’ll cut this discussion short here. (Email me or send us a <a href="https://www.facebook.com/joidesresolution/">Facebook<</a> message if you want to know more about the effect of water on rock behavior at elevated temperatures and pressures. You’ll find my email in my blogger profile.)</p>
<p class="p1">Once the sediments are cemented together, possibly including compaction, they are no longer easy to break apart. They’re now hard and solid on a larger scale, not just individual hard and solid particles. This process of sediments turning into rocks is called <strong>lithification</strong>. “Lithos” means “rock” in Greek. Keep an eye out for that word root! Lithology, lithography, monolith, lithic fragments…</p>
<p class="p1">There are of course other ways of making rocks, but we’ll leave <dfn title="Look up the definition of Igneous.">igneous</dfn> and metamorphic rocks for another time.</p>
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<title>A Successful Story at Site U1480</title>
<link>https://joidesresolution.org/a-successful-story-at-site-u1480/?utm_source=rss&utm_medium=rss&utm_campaign=a-successful-story-at-site-u1480</link>
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<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Fri, 09 Sep 2016 22:05:00 +0000</pubDate>
<category><![CDATA[drilling]]></category>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[Expedition 362 Sumatra Seismogenic Zone]]></category>
<category><![CDATA[operations]]></category>
<category><![CDATA[Sumatra Seismogenic Zone operations]]></category>
<guid isPermaLink="false">https://joidesresolution.org//a-successful-story-at-site-u1480</guid>
<description><![CDATA[We finished our first site with success! We’re now at our second site, so here’s a little summary of what... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/a-successful-story-at-site-u1480/" title="Continue reading A Successful Story at Site U1480">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p>We finished our first site with success! We’re now at our second site, so here’s a little summary of what we did at Site U1480. We met our primary science goal at the site: core the entire sedimentary sequence from seafloor down to the oceanic crust that forms the basement that the sediments rest on. That’s almost 1.4 km (0.8 mi)!<br />
<!--break--></p>
<p>While the scientists are writing up their reports, we’ll summarize a few of the things that we’ve been thinking about. I’ll have a few more posts for you in the next few days. Stay tuned!</p>
<p>(Click on the image at left to see it bigger.)
</p>
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<title>Weekend Specials</title>
<link>https://joidesresolution.org/weekend-specials/?utm_source=rss&utm_medium=rss&utm_campaign=weekend-specials</link>
<comments>https://joidesresolution.org/weekend-specials/#respond</comments>
<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Mon, 05 Sep 2016 01:04:23 +0000</pubDate>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[Expedition 362 Sumatra Seismogenic Zone food fun]]></category>
<category><![CDATA[food]]></category>
<category><![CDATA[fun]]></category>
<category><![CDATA[Sumatra Seismogenic Zone]]></category>
<guid isPermaLink="false">https://joidesresolution.org//weekend-specials</guid>
<description><![CDATA[It’s the weekend! That means everything proceeds as normal on board, except on-shore colleagues don’t read their emails, we don’t... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/weekend-specials/" title="Continue reading Weekend Specials">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p>It’s the weekend! That means everything proceeds as normal on board, except on-shore colleagues don’t read their emails, we don’t have video conferences with schools, and we have Very Special Food.<br />
<!--break--></p>
<p>The food is always good, but on the weekends it’s exceptional. Every Saturday has a barbecue, but I’ve already mentioned that. What’s worth its own post are the desserts and the array of options. All dessert photo credits go to our Staff Scientist, Katerina Petronotis. <img decoding="async" alt="baked_alaska1" src="/sites/default/files/u375/baked_alaska1.jpg" style="border:0px solid;margin:5px;" /></p>
<p><img decoding="async" alt="baked_alaska2" src="/sites/default/files/u375/baked_alaska2.jpg" style="border:0px solid;margin:5px;" /></p>
<p>This is a Baked Alaska, oblique arial view of whole feature and fresh surface in cross section. 20 cm plate for scale. </p>
<p><img decoding="async" alt="lava_cake" src="/sites/default/files/u375/lava_cake.jpg" style="border:0px solid;margin:5px;" /></p>
<p>This is a lava cake, in perpendicular arial view. Small soup spoon and standard ice cream scoop for scale. Although internal features are difficult to discern, repeated excavations indicate the chocolate cake shell is filled with warm caramel sauce that can be seen escaping here through fissures in the cake edifice due to pressure gradients. Flavor density is extremely high, ranking 9.75/10 for volcanologist/sedimentologist Steffen. Steffen has sailed on several expeditions and is an expert in both desserts and volcanoes, making him a uniquely qualified evaluator of these features. </p>
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<title>What’s an Earthquake?</title>
<link>https://joidesresolution.org/whats-an-earthquake/?utm_source=rss&utm_medium=rss&utm_campaign=whats-an-earthquake</link>
<comments>https://joidesresolution.org/whats-an-earthquake/#respond</comments>
<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Tue, 30 Aug 2016 18:49:35 +0000</pubDate>
<category><![CDATA[earthquakes_659]]></category>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[Geology and earth science_719]]></category>
<category><![CDATA[Plate-Tectonics]]></category>
<category><![CDATA[seismicity]]></category>
<category><![CDATA[seismogenesis]]></category>
<category><![CDATA[Sumatra Seismogenic Zone]]></category>
<guid isPermaLink="false">https://joidesresolution.org//what%e2%80%99s-an-earthquake</guid>
<description><![CDATA[Earthquakes may bring to mind fear and danger or perhaps confusion and curiosity. Some earthquakes can be very destructive, as... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/whats-an-earthquake/" title="Continue reading What’s an Earthquake?">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p>Earthquakes may bring to mind fear and danger or perhaps confusion and curiosity. Some earthquakes can be very destructive, as we have seen in several recent events. To help mitigate the damage and loss of life, earthquake scientists aim to better understand the physical context of great earthquakes, like the 2004 M 9 Sumatra-Adaman Earthquake. That’s part of the goal of Expedition 362. But first, we need to know what an earthquake is.</p>
<p>A tectonic earthquake is <em>sudden slip along a fault and the associated release of seismic energy</em>. There are other types of earthquakes, such as those associated with volcanoes, but here we focus on tectonic earthquakes. Let’s unpack the definition piece by piece.</p>
<h4>Sudden:</h4>
<p class="p1">Seconds to minutes is the timescale for a typical earthquake*. The larger the earthquake, the longer it lasts. I’ve experienced a few M 4 to M 5.5 earthquakes. They lasted about 10 seconds. The 2004 Sumatra earthquake, M > 9, lasted between 3 and 4 minutes.</p>
<h4></h4>
<h4>Slip along a fault:</h4>
<p class="p1">A fault is a surface that exists in three dimensions underground. Faults can be as tiny as a few millimeters long/wide and as large as thousands of kilometers long and up to hundreds of kilometers wide into the subsurface (if it makes a shallow angle to the surface). Faults have two sides that move past each other, usually in jumps and starts because friction keeps them from sliding smoothly past each other. These jumps and starts are the earthquakes, and the jump distance along the fault surface is called “slip”. This slip starts in one location, the hypocenter, and then breaks through the rocks on the fault surface. This breaking is called “rupture”, and the resulting ruptured area is sometimes called the “slip patch”, the area on the fault that moved during the earthquake. What controls the area of the slip patch is another story for another time, but for now remember that the bigger the area, the bigger the earthquake.</p>
<h4></h4>
<h4>Associated release of seismic energy:</h4>
<p class="p1">We measure the energy released in terms of earthquake magnitude. Earthquakes release a tremendous amount of energy. For example the Sumatra M9 earthquake released about 3 x 10^17 Joules—that’s 475 megatons of TNT or 23,000 times as much energy as an atomic bomb (<a href="http://authors.library.caltech.edu/23887/1/Kanamaori2006p9007Earthquakes_Radiated_Energy_And_The_Physics_Of_Faulting.pdf">Kanamori, 2006</a>).</p>
<p class="p1">In order to be released, the energy must first be stored. This is a basic necessity for making earthquakes possible: building up elastic potential energy in the rocks on either side of a fault, with friction on the fault holding the sides together without sliding (yet!). This is like stretching a rubber band. If you let go, it bounces back to its original length because it’s elastic. It can make that change because you’ve given it elastic potential energy that gets stored until you let go—or until the rubber band breaks. The fact that tectonic plates are always moving is the key to the build up of strain energy and its release as an earthquake. Strain energy builds up over tens, hundreds, or even thousands of years as the plates move past one another. Eventually the stresses along the locked portions between plates overcome the friction and all the accumulated energy is released as kinetic energy (motion), heat energy, and seismic wave energy. The motion along a slip patch can stretch or compress areas away from the fault, which may cause other faults to rupture. This is one of the reasons for aftershocks.</p>
<h4>Ground motion:</h4>
<p class="p1">How much shaking we feel depends on a lot of factors including how close we are to the hypocenter (see diagram) and the type of rock transmitting the earthquake. Just like sound travels differently through water and air, as you know from playing the game “telephone” in the pool, seismic waves travel differently through different kinds of rock. You can get a feel for this by striking different tiles of rock or other material with a mallet from your friends’ xylophone (ask permission first). The higher pitch you hear from hitting the surface of the rock tile versus the cement block means the sound waves can travel faster through the rock tile. The closer you are to the hypocenter, the more shaking you’ll feel. Also harder rock is more efficient at transmitting energy. This is why the M 5.8 earthquake in Virginia in August 2011 was felt far away from Virginal, but an earthquake of the same size in my hometown in central-coast California may only be felt by people living very close by.</p>
<p class="p1">We tend to think of earthquakes as points and of faults as lines. Faults are complex structures that exist in three dimensions (though we usually draw them in two, on a map or on a cross section). They can be rough or smooth or deep or shallow. Earthquakes are also a combination of different types of movement over an area. This combined complexity makes faults and earthquakes both difficult and fascinating to study, and their effects on humans make them urgent topics of research.</p>
<p class="p1">*Earthquake scientists have recently described releases of seismic energy that last much longer than minutes—days to years—and share some characteristics with typical earthquakes. They call these “slow-slip events”. You can read more about them <a href="http://earthweb.ess.washington.edu/vidale/John_Vidale/Pubs_08-now_files/Phys_Today_2012.pdf" target="_blank" rel="noopener">here<</a>, though the explanation is fairly technical since it’s written for a physics audience.</p>
<p class="p1">**Update** I just came across <a href="http://www.smithsonianmag.com/science-nature/slow-earthquakes-are-thing-180960248/?no-ist" target="_blank" rel="noopener" class="broken_link">this more accessible article in the Smithsonian Magazine<</a>. We wonder on Exp 362 if perhaps some of what we’ll find in terms of sediment strength could help clarify the mechanics of slow slip events.</p>
<p class="p1">I can write a blog post about SSEs if you’re really curious. Write the JR a message on <a href="https://www.facebook.com/joidesresolution/" target="_blank" rel="noopener">Facebook<</a> or <a href="https://www.twitter.com/TheJR" target="_blank" rel="noopener" class="broken_link">Twitter<</a>.</p>
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<title>Today in Geology History: In Memory of Marie Tharp, Pioneering Oceanographer</title>
<link>https://joidesresolution.org/today-in-geology-history-in-memory-of-marie-tharp-pioneering-oceanographer/?utm_source=rss&utm_medium=rss&utm_campaign=today-in-geology-history-in-memory-of-marie-tharp-pioneering-oceanographer</link>
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<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Wed, 24 Aug 2016 03:26:02 +0000</pubDate>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[Geography_709]]></category>
<category><![CDATA[history of geology]]></category>
<category><![CDATA[Sumatra Seismogenic Zone]]></category>
<category><![CDATA[women in science]]></category>
<guid isPermaLink="false">https://joidesresolution.org//today-in-geology-history-in-memory-of-marie-tharp-pioneering-oceanographer</guid>
<description><![CDATA[Think of the first time you saw a map of the world. It probably looked like colorful patches mostly connected... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/today-in-geology-history-in-memory-of-marie-tharp-pioneering-oceanographer/" title="Continue reading Today in Geology History: In Memory of Marie Tharp, Pioneering Oceanographer">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p class="p1">Think of the first time you saw a map of the world. It probably looked like colorful patches mostly connected to other colorful patches, with a vast scape of blue between the colorful areas. Until the 1940s, that’s how many people imagined the ocean: “a <span class="s1">uniform, featureless blue border for the continents.”* These are the words of Marie Tharp, one of the people who created the first maps of the world’s oceans. She passed away ten years ago today (23 August 2016), at the age of 86. Her initial path to <a class="glossary-term" href="http://archive.joidesresolution.org/glossary/9#term390"><dfn title="Look up the definition of Geology.">geology</dfn></a> and oceanography was as non-linear as it is inspiring. Her decades of dedication and curiosity set the foundation of the theory of plate tectonics and made it possible for us to do the work we’re doing today in geology and on this expedition. </span></p>
<p class="p1"><span class="s1">Tharp was born in Michigan in 1920. Her father was a soil surveyor for the United States Department of Agriculture, a job which moved the family frequently all over the US. “I guess I had map-making in my blood, though I hadn’t planned to follow in my father’s footsteps,” Marie wrote in an autobiographical chapter. Instead, she followed an unusual path for women in her time. In the 1940s, </span>new opportunities opened to women while men went to fight in World War II. In 1943, Tharp and about ten other women responded to a University of Michigan advertisement for women to study geology, with a promise of jobs in the petroleum industry. After graduating, Tharp was still not quite satisfied with her work. “<span class="s1">Some of the girls I went to school with went into micropaleontological work and spent their time looking through microscopes. That seemed tedious, so I went to the University of Tulsa and got a degree in math.” Then, in 1948 she went to New York to look for new prospects. She found her way to Columbia University, where she was hired to work with Maurice “Doc” Ewing, a geologist at the Lamont Geological Observatory (now the Lamont-Doherty Earth Observatory). Soon she worked full time for graduate student Bruce Heezen, creating hand-drawn profiles of the seafloor from sounding technology developed for the Navy during the war. (We still use sonar to map the seafloor. On every expedition of the JR, when we’re in transit, we hear a little chirp every few minutes, sending sound waves through the water that bounce off the seafloor and come back to receivers on board. We send the data to a centralized location that continues to gather data about the seafloor. ) </span></p>
<p class="p1"><span class="s1">Tharp translated tends of thousands of depth measurements collected by several ships during the 1940s – 1960s. From a criss-crossing web of ship’s tracks over the Atlantic, Tharp created “a hodgepodge of disjointed and disconnected profiles of sections of the North Atlantic floor”, which took her nearly two months to organize into a geographically meaningful arrangement. When she did, she noticed a pattern in the location and shape of a prominent feature roughly in the middle of the Atlantic: “the only consistent match-up was a V-shaped indentation in the center of the profiles.” Previous explorations had suggested submarine mountain chains, but Tharp noted that only the valley was continuous along the north-south axis of the long feature. She interpreted this as a rift valley, like we see today from Syria to eastern Africa. Heezen, whose lab she was working in, initially wrote off her work as impossible, related to the as-yet unsupported idea of continental drift. He called it “girl talk”. </span></p>
<p class="p1"><span class="s1">Unwilling to let go of what she thought was right, Tharp continued to search for more evidence of a rift valley. “If there were such a thing as continental drift, it seemed logical that something like a mid-ocean rift valley might be involved.” It would be a place where upwelling of material from beneath the crust would push the two sides of the valley apart. She and Heezen adapted physiographic mapping techniques used on land for mapping the bottom of the ocean. </span>Increasingly precise sounding data, the advent of satellite positioning, and increasing numbers of research vessels improved the maps. Another layer of data soon proved Tharp right about the rift valley. Heezen and Ewing showed that earthquakes could trigger <a class="glossary-term" href="http://archive.joidesresolution.org/glossary/9#term865"><dfn title="Look up the definition of Turbidity currents.">turbidity currents</dfn></a> (slurries of sediment carried by turbulent water that flows as its own current along the ocean floor) and destroy cables on the seafloor. Elevated interest in earthquake locations to determine safe cable-laying locations led to a map that showed earthquakes occurring along Tharp’s delineated “gully”.</p>
<p class="p1">They broadened their view to look at the global distribution of these oceanic ridge-sided valleys. With the global earthquake maps layered on the light table, they noted the coincidence of shallow earthquakes and <a class="glossary-term" href="http://archive.joidesresolution.org/glossary/9#term1144"><dfn title="Look up the definition of mid-ocean ridge.">mid-ocean ridge</dfn></a>s, not just in the Atlantic but also in the Indian Ocean, the Gulf of Aden, the Arabian Sea, and the Red Sea. They all matched up with the valleys, and the ocean ridges extended all around the world. Amid both scorn and celebration at international scientific meetings, the evidence continued to expand.</p>
<p class="p1">Over the next decade, Heezen and Tharp overcame political, personal, and gender barriers to sail on research cruises, gather more data from all over the world, and even collaborate with Russian scientists amid Cold War political hostility. The quality and detail of the maps improved alongside ocean exploration technology. Their first major published maps were drawn by hand from the soundings and ship tracks, interpreted as well as possible in areas with no data. “<span class="s1">Like the cartographers of old, we put a large legend in the space where we had no data. I also wanted to include mermaids and shipwrecks, but Bruce [Heezen] would have none of it.” </span>By the end of the 1960s, the integrative theory of plate tectonics was coming together, in large part based on Tharp’s maps and the understanding that came with them.</p>
<p class="p1">Today on the JR, we’re in the eastern Indian Ocean, and the seafloor beneath us was mapped in part by Tharp only about 60 years ago. We’ve only recognized the existence of subduction zones like the Sunda subduction zone we’re here to learn more about within the past 50 years. We’re still learning about what drives these systems and contributes to the locations of earthquakes all over the world—thanks to Tharp, and many others like her, who pushed the limits of science past barriers of gender, nation, and accepted ideas. Here’s to many more years of exploration and innovation.</p>
<p class="p1">In her memory, here are many of the women on the current research cruise of the JR, Expedition 362: Sumatra Seismogenic Zone. We have a high percentage of women on this cruise (39% among the scientists and technicians)! (Photo by Tim Fulton)</p>
<p class="p1">* quotes of Marie Tharp come from this excerpt of an autobiographical chapter written by Marie Tharp in a collection of perspectives on the early years of what’s now the Lamont-Doherty Earth Observatory. <a title="http://www.whoi.edu/sbl/liteSite.do?litesiteid=9092&articleId=13407 " href="http://www.whoi.edu/sbl/liteSite.do?litesiteid=9092&articleId=13407%C2%A0">http://www.whoi.edu/sbl/liteSite.do?litesiteid=9092&articleId=13407 <</a> A nice reminder that paths through life are rarely linear, and pursuing something you love, are good at, and can get paid for can be a journey with great reward.</p>
<p class="p1"><u>Further Reading</u></p>
<p class="p1">Short biographical entry from Columbia, where she used to teach: <a href="http://c250.columbia.edu/c250_celebrates/remarkable_columbians/marie_tharp.html">http://c250.columbia.edu/c250_celebrates/remarkable_columbians/marie_tharp.html<</a></p>
<p class="p2">Award press release from Columbia on the occasion of her receiving the University’s Heritage Award: <a href="http://www.columbia.edu/cu/news/01/07/marieTharp.html" class="broken_link">http://www.columbia.edu/cu/news/01/07/marieTharp.html<</a></p>
<p class="p2">What looks like a delightful children’s book about her: <a href="https://www.amazon.com/Solving-Puzzle-Under-Sea-Marie/dp/1481416006/ref=sr_1_1?ie=UTF8&qid=1471991850&sr=8-1&keywords=solving+the+puzzle+under+the+sea">https://www.amazon.com/Solving-Puzzle-Under-Sea-Marie/dp/1481416006/ref=sr_1_1?ie=UTF8&qid=1471991850&sr=8-1&keywords=solving+the+puzzle+under+the+sea<</a></p>
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<title>The best room on the ship</title>
<link>https://joidesresolution.org/the-best-room-on-the-ship/?utm_source=rss&utm_medium=rss&utm_campaign=the-best-room-on-the-ship</link>
<comments>https://joidesresolution.org/the-best-room-on-the-ship/#respond</comments>
<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Tue, 23 Aug 2016 02:57:49 +0000</pubDate>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[food]]></category>
<category><![CDATA[Life at sea_711]]></category>
<category><![CDATA[Sumatra Seismogenic Zone]]></category>
<guid isPermaLink="false">https://joidesresolution.org//the-best-room-on-the-ship</guid>
<description><![CDATA[You can argue about this–perhaps the Core Lab, the Chem Lab, the Gym, one’s own cabin–but I think the best room... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/the-best-room-on-the-ship/" title="Continue reading The best room on the ship">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p>You can argue about this–perhaps the <a class="glossary-term" href="http://archive.joidesresolution.org/glossary/9#term414"><dfn title="Look up the definition of Core Lab.">Core Lab</dfn></a>, the Chem Lab, the Gym, one’s own cabin–but I think the best room on board is the Mess Hall or <a class="glossary-term" href="http://archive.joidesresolution.org/glossary/9#term375"><dfn title="Look up the definition of Galley.">Galley</dfn></a>. The place we enjoy all our meals and cookie breaks together.</p>
<p>I’m sorry I’ve been a bit quiet on the science. We’re drilling a new hole, and putting a metal casing inside that hole so that we can drill down and collect core from even deeper (800-1400 <a class="glossary-term" href="http://archive.joidesresolution.org/glossary/9#term1012"><dfn title="Look up the definition of Mbsf.">mbsf</dfn></a>). Agnes will update you on that process soon! The scientists have been awaiting new core and catching up on writing reports and finishing sampling. In the meantime, I’ve been learning a lot about drilling operations, subduction zones, and some background info for future posts! I’ve also been getting to know the scientists and crew a bit better. They’re a great bunch! So it’s especially delightful to share wonderful meals and snacks with them.</p>
<p>The Camp Boss, Paul, must be a magician, with a very able team of 4 cooks and a baker. The array of food present at every meal–keep in mind there are four in 24 hours, and any one might be any meal of the day for someone–is astounding. Small fridges on the countertops are always (so far) stocked with juice, yogurt, and spectacular desserts. The salad bar still has fresh vegetables and excellent home-made hummus. The fruits remain piled high (see teaser photo background!), next to a counter with ever-present pastries. The hot food line is a buffet of stewed and well-spiced veggies, meats, and soup. You can get eggs to order at any meal. It’s good there’s a gym, heavy lifting of core sections, and lots of running up and down stairs between decks to make us hungry enough to eat all the bounty!</p>
<p>Saturday is barbecue day, weather permitting. Special desserts (in addition to the usual excellence) appear on weekends as well! We don’t get any days off for the two months we’re on board, so a little special treat on certain days marks the time and gives us a sense of a break.</p>
<p>On top of all that, I appear at the hot food line and declare I’m vegetarian (nicely, of course…). They cook up separate food for the vegetarians (we’re 6 among the 35 scientists+educators), and serve it to us in delightful arrangement. You can see my colorful plate in the photo above. They know us all by name, and call out our dishes when they’re ready!</p>
<p>Here’s a photo from our first Saturday barbecue. Last week was a bit rainy, so we stayed inside. It’s been about 30ºC/68ºF every day, but the wind and humidity and rain can change how that feels. Hold on to your hat and your lettuce while you look at the photo!</p>
<p> </p>
<p><img loading="lazy" decoding="async" class="alignnone size-full wp-image-23633" src="https://joidesresolution.org//wp-content/uploads/2016/08/DSC_3025.jpg" alt="" width="640" height="419" srcset="https://joidesresolution.org/wp-content/uploads/2016/08/DSC_3025.jpg 640w, https://joidesresolution.org/wp-content/uploads/2016/08/DSC_3025-300x196.jpg 300w" sizes="auto, (max-width: 640px) 100vw, 640px" /></p>
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<title>Scales Are Not Just For Fish: Time and Space in Geology</title>
<link>https://joidesresolution.org/scales-are-not-just-for-fish-time-and-space-in-geology/?utm_source=rss&utm_medium=rss&utm_campaign=scales-are-not-just-for-fish-time-and-space-in-geology</link>
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<dc:creator><![CDATA[Naomi Barshi]]></dc:creator>
<pubDate>Fri, 19 Aug 2016 17:44:17 +0000</pubDate>
<category><![CDATA[core]]></category>
<category><![CDATA[EXP362]]></category>
<category><![CDATA[geologic time]]></category>
<category><![CDATA[Geology_482]]></category>
<category><![CDATA[rates]]></category>
<category><![CDATA[Sedimentation]]></category>
<category><![CDATA[Sumatra Seismogenic Zone]]></category>
<guid isPermaLink="false">https://joidesresolution.org//scales-are-not-just-for-fish-time-and-space-in-geology</guid>
<description><![CDATA[Blog Series Installment #2: Space as Time When you make a layer cake, you lay the first slab of cake... <div class="read-more"><a class="excerpt-read-more" href="https://joidesresolution.org/scales-are-not-just-for-fish-time-and-space-in-geology/" title="Continue reading Scales Are Not Just For Fish: Time and Space in Geology">Read more<i class="fa fa-angle-right"></i></a></div>]]></description>
<content:encoded><![CDATA[<p>Blog Series Installment #2: Space as Time</p>
<p class="p1">When you make a layer cake, you lay the first slab of cake on the platter, then icing, then the next layer, then more icing, and so on. You’re a scientist, so you did an experiment with the layers of the cake. You baked some thicker than others, and discovered that they took more time to bake. The time you’re done with the cake, with your variety of layers in a stack, the layer at the bottom is oldest, and thicker layers took longer to form. (Sure, you could flip the cake over or cut it up and turn some chunks over, but we’ll leave that for a post about deformation of rock units and structural <a class="glossary-term" href="http://archive.joidesresolution.org/glossary/9#term390"><dfn title="Look up the definition of Geology.">geology</dfn></a>.)</p>
<p class="p1">This depth-age and thickness-time relationship is also generally true in what we affectionately call “layer cake geology”. This is approximately what we’re looking at in the cores of Expedition 362, except that thicker layers aren’t always the ones that took longer to form. We’ve recovered layer upon layer of different combinations of mud and sand, varying in color from grey to green to beige depending on the minerals that comprise them. (In geology, mud is a technical term! It means a combination of silt-sized and clay-sized particles—anything smaller than about 1/10 of a mm, which is smaller than you can usually see without magnification.) This is what we expect to find at the bottom of deep ocean water, which is mostly very quiet. Even the tiniest particles can settle out of it. As they do so, they make layers upon layers, oldest at the bottom, youngest at the top.</p>
<p class="p1">In this way, space becomes time: the deeper we go, the older the sediments get. Our micro-paleontologists have confirmed this for us, which is very comforting! The sediments coming up during my shift from around 500 meters (~1650 ft) below the seafloor are already several million years old (late Miocene, for the geologists), more than twice as old as the first humans!</p>
<p class="p1">Space and time have another important relationship, if we know how fast things happen. The cake you baked above had thicker layers that took longer to bake than the thinner layers. The process of baking the same mixture of flour, eggs, sugar, etc., that you used in all your cake layers goes at a certain rate, perhaps 1 unit of baked-ness per minute. Baking different kinds of things takes a different amount of time. Likewise, how long it takes for different types of sediments to accumulate on the seafloor varies. Sometimes thickness and how long something took to form aren’t exactly the same thing.</p>
<p class="p1">The photo-stitch of a segment of core below illustrates a few things that our scientists have been looking for and interpreting on this expedition. This segment of core, like many we’ve seen on board, is a reminder that a thicker layer does not always mean it took longer to form. Sometimes, thick layers of sandy sediment like this only took a few minutes to form! These could be the result of an underwater landslide or a fast-moving current of water that slowed down all at once and dumped a lot of coarser sediment because it couldn’t carry it any longer. In contrast, the few centimeters of clay-rich, compact mud at the top of the photo probably took thousands of years to accumulate by the slow settling of tiny particles out of the ocean water above.</p>
<p class="p1">This segment of core also reminds us that we don’t always know the answer right away. Two geologists might not always have the same interpretation. We only get to see a little bit of core at a time, a few centimeters in diameter, which isn’t the whole picture. Still, we can use the combination of all our different expertise to put together a bigger picture than what’s on the table in front of us. That’s why these expeditions bring on board a group of scientists with a wide range of knowledge, all working towards related questions that need different tools and eyes and minds to be answered.</p>
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