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Lava Lake at Erta Ale Lava lakes are a relatively rare phenomenon; currently only seven are known to exist in the world (an eighth, at Kilauea volcano, drained away in 2018). The lava lake in this photo is located in the summit caldera of Erta Ale volcano in the Erta Ale Range of Ethiopia.
Melting points
This ancient piece of rock shows an interesting interaction between two different types of igneous rock.
Light colored igneous rocks are called felsic after the minerals quartz and feldspar which are abundant in light-colored igneous rocks, while dark colored igneous rocks are called mafic after magnesium and iron (ferric) which are abundant in those.
The mafic pieces of this rock are broken, angular, and surrounded by the felsic rock. The felsic rock intruded the mafic rock, breaking it apart into pieces. For this to happen, the mafic rock had to be a solid while the felsic rock was a liquid, able to flow around the sharp, angular chunks.
The melting point of felsic rocks is lower than the melting point of mafic rocks, by as much as 300 to 400°C, so the felsic magma was able to press into the mafic rock, break it into pieces, and even flow around it without melting or absorbing it.
-JBB
Image credit: https://flic.kr/p/bt4Tv1
rhyolitic lava is the coolest kind of lava
Hurricane Harvey fed off record warm Gulf of Mexico waters
This satellite shot captures Hurricane Harvey at the time it was a category 4 storm, just before it made landfall in Texas. The storm started off as a disturbance crossing the Yucatan Peninsula, but when it made it into the warm waters of the Gulf of Mexico it rapidly strengthened. Harvey became the second costliest disaster ever to hit the United States after it doused the city of Houston with record rainfall totals. A new analysis points squarely at the Gulf of Mexico as the main driving force behind the power of this storm.
Hurricanes feed off of warm temperatures in ocean waters. In the process, they remove heat from the ocean and leave the water behind it cooled off. However, other things can happen that affect ocean temperatures; for example, the winds blowing over the water could mix the shallow layer with deeper water, cooling the surface water by pushing the warm water deeper. As a consequence, it’s not easy for scientists to match up the energy of the storm with the energy of the ocean.
Harvey though represented a unique case. For much of the surrounding month it was the only major weather event in the Gulf of Mexico, and it traveled over areas that are well instrumented so that scientists could see how much heat it removed from the water. On top of that, scientists also have available the Global Precipitation Measurement Satellite system, which enabled estimates of Harvey’s rainfall over wide areas.
A team led by a scientist at the National Center for Atmospheric Research took these two measurements and converted them into total energy. The ocean cooled by a certain amount over a certain volume – that’s an energy measurement. Harvey produced a certain amount of rainfall over a certain area – that’s also an energy measurement. When they compared the number of joules pulled out of the Gulf to the energy released over land by Harvey – they were virtually identical, within 1% of each other. The energy that drove Harvey was the energy in the Gulf; basically every Joule of energy it pulled out of the Gulf, it dumped on Texas.
Harvey became such a disaster because it had an ample supply of energy in the shallow waters of the Gulf of Mexico. Prior to the storm, the waters of the Gulf were at their hottest temperature ever recorded, more than 1.5°C above the long term average. Those temperatures extended downwards, making the Gulf heat content also a record. When Harvey passed over these waters, it cooled them by 2°C. That extra 1.5°C in the Gulf of Mexico in 2017 was enough to almost entirely fuel the storm; had the Gulf not been at record temperatures, Harvey would not have had the energy to produce that rainfall.
Global ocean heat content has been rising steadily since the 1980s as the ocean takes up much of the extra heat kept in the atmosphere by greenhouse gases. The close match between energy taken out of the ocean and energy dumped by the storm verifies that the extra energy trapped in the atmosphere is feeding storms like Harvey. The extra heat in the Gulf of Mexico directly triggered flooding in Houston, and as ocean temperatures continue to increase, it will be able to continue powering devastating storms.
-JBB
Original paper: https://doi.org/10.1029/2018EF000825
Mineral transformations drove biggest deep quake
A little over ninety years ago, British geophysicist Herbert Hall Turner noticed some earthquake data that suggested a surprising explanation. The only way to explain it was if the quake had occurred hundreds of kilometres beneath the Earth's surface, instead of the more commonly seen near-surface earthquakes.
Since Turner's observations, deep earthquakes have fascinated seismologists. It is still unclear why they happen, but two studies just published in the journal Science, taking different approaches, conclude that they are probably a result of rapid changes in minerals at that depth.
Such deep earthquakes do not have immediate consequences for humans. But they hold clues about destructive quakes in the Earth's shallower crust, making it important to understand them. Not just superficial
Most earthquakes occur in the stiff, brittle outer shell that includes the Earth's crust. This "seismogenic zone", which causes the most devastating and dangerous earthquakes, goes down to about 15 km beneath the surface.
As you go deeper, pressure and temperature both increase rapidly, so the nature of earthquakes changes. Rocks move slowly, speaking on geological time scales, when pushed or pulled by different forces acting on them. At depth, they appear to flow like soft toffee, rather than break like peanut brittle.
This is why Turner's observations of earthquakes more than 600 km below the surface were puzzling. If the rocks flow slowly, then there shouldn't really be any sudden shocks that cause an earthquake. Rather, there should be gentle continuous readjustments to stress.
Suggestions have been floated in the past about what triggers such earthquakes. But Thorne Lay of University of California Santa Cruz Lay's took a step ahead to analyse a deep earthquake that occurred this year on May 24, in the Pacific Ocean beneath the Okhotsk plate. At a magnitude of 8.3, it was four times greater than the 1906 San Francisco earthquake. Indeed, it was the biggest ever recorded at a depth of more than 600km. A near-surface earthquake of the same magnitude could've been very destructive, but at that depth it was barely noticeable at the surface above.
Recent analysis of an earthquake at Bhuj, India in 2001 suggests it shared similarities to the Okhotsk event, although it was just 16km deep. In contrast, however, it caused terrible devastation, including an estimated 20,000 deaths. "There may be things we don't understand about more shallow earthquakes that we can learn from studying these deep earthquakes" Dr Bob Myhill of the University of Bayreuth, Germany, said.
During the Okhotsk event, the Pacific plate of Earth's crust was drawn down into the hot mantle that makes up much of the planet's interior. What Lay found was that the seismic energy released in the event was so large that it caused fractures as great as 180km long below the surface. The rock ruptured at close to the speed of sound, which in the rock would be as much as 14,000 km/h.
But what caused such rapid rupture? Alexandre Schubnel of Ecole Normale Supérieure suggests an explanation, which hinges a the mineral making up the deep rock, called olivine. To be sure he designed lab experiments that could mimic deep Earth.
Schubnel found that above a critical temperature and pressure, olivine changes into another mineral called spinel. Under stress, this sudden change creates fractures, much like those seen in the earthquake. The mineral change releases stress instantaneously, in just the same way as stress was relieved in the deep earthquake under the Pacific Ocean.
There is one critical difference, however. To make the experiments easier, the olivine used by Schubnel in the lab contained the element germanium instead of silicon. Germanium-olivines are known to behave slightly differently than silicon-olivines, and this may make a lot of difference 600km below the surface.
Still, while the mini-earthquakes seen in the lab were a million billion times smaller than what those in the Earth, the reason these experiments can be trusted is because the creaks and groans of minerals in a lab show similar characteristics as that of large earthquakes. So, even though Suchbnel's idea is not new, it confirms experimentally suggestions made by researchers before. It opens the way to studying deep Earthquakes in the safety and comfort of the lab.
~SATR
image: San Carlos olivine crystal close up ... http://skywalker.cochise.edu/wellerr/mineral/olivine
Geology kitty!
Graphic granite.
Looking like an ancient Sumerian clay tablet engraved with cuneiform writing, this rock formed during the crystallisation of a magma. As the temperature dropped below a tipping point, the pink feldspar and grey quartz separated out from each other in a process called exsolution, and grew simultaneously at a constant gentle rate to form this texture. Graphic texture is not limited to the magmas of silica rich granites (known as leucogranites, the prefix leuco indicating siliceous richness), but is most commonly found in them, particularly in pegmatites, the last silica and rare element rich remnants of already crystallised granites, accounting for the usual absence of any dark minerals such as mica or hornblende.
Loz
Sample from Knickel's feldspar quarry at Bedford, NY, originally in the USGS Petroographic Collection, now in the Smithsonian's.
Image credit: Ken Larsen/Smithsonian Institution.
A paper on its origin: http://www.minsocam.org/ammin/AM71/AM71_325.pdf
http://www.mindat.org/min-39400.html
This is a lenticular cloud, formed by air blowing in the wind and being forced upwards where it cools adiabatically forming a cloud. Thermodynamics in the atmosphere above a volcano. If you thought I was going to close this last #RIPVine binge with anything else, follow this page for a little while and you’d probably predict that.
Orographic cloud over Corsica.
Resembling a spider's nest, this cloud formed when warm moist Mediterranean winds were forced to rise in order to pass over the island, resulting in cooling and condensation.
Loz
Image credit: Karen Nyberg.
Metamorphic rock heated above its melting temperature and starting to segregate into solid darker layers and lighter molten layers.
Mentos and Volcanoes
By now, most people know that dropping mentos into a bottle of coke produces an eruption of sugary foamy goodness that coats everything in the immediate vicinity, much to the delight of everyone’s inner 7 year old. Now imagine this end result on a much larger scale, and no, I don’t mean with mentos and a bath of coke.
Researchers from Sweden and Italy have found that when magma encounters carbonate rocks (limestone and marble) at a relatively shallow depth in the crust, they interact to release carbon dioxide. At significant depths gases remain in solution within a magma due to the enormous amount of pressure from overlying crust, but at a shallower depth gases can form bubbles within the magma. It is at these depths that when encountering a carbonate rock the magma causes a rapid degradation and degassing of the carbonates, releasing carbon dioxide gas into the magma. This addition of CO2 increases the explosive potential of magma, and any volcanoes fed by it.
Volcanoes such as Vesuvius and Merapi are fed by magmas that interact with underlying carbonates and their interaction may contribute to their infamously explosive eruptions that have occurred in the past. A better understanding of this mechanism and its contribution to the behavior of volcanoes influenced by it could potentially be an asset when assessing the risk a volcano poses.
While the reaction of coke and mentos is an entirely different process to that which occurs between carbonates and magma, I couldn’t resist the visual comparison. Just don’t go throwing chunks of limestone into volcanoes.
RJW
Image Credits Vesuvius - Sigmund - http://bit.ly/2bnzPBv
Fig 3 - Deegan, F.M., Troll, V.R., Freda, C., Misiti, V., Chadwick, J.P., McLeod, C.L. and Davidson, J.P., 2010. Magma–carbonate interaction processes and associated CO2 release at Merapi Volcano, Indonesia: insights from experimental petrology. Journal of Petrology, 51(5), pp.1027-1051. - http://bit.ly/2b397u7
Further Reading
Deegan, F.M., Troll, V.R., Freda, C., Misiti, V., Chadwick, J.P., McLeod, C.L. and Davidson, J.P., 2010. Magma–carbonate interaction processes and associated CO2 release at Merapi Volcano, Indonesia: insights from experimental petrology. Journal of Petrology, 51(5), pp.1027-1051. - http://bit.ly/2b397u7
Limestone assimilation under volcanoes helps understand Earth’s carbon cycle - http://bit.ly/2bm0e0r
Diet Coke and Mentos eruption - http://bit.ly/1IpyJ13
I have a question, can ice dissolve in liquid oxygen?As oxygen can dissolve in water please
Woo hoo, it’s a thermodynamic thursday!
Let’s start by thinking about these fluids the other way. Under standard temperature and pressure, water will be a liquid and oxygen will be a gas. Oxygen doesn’t dissolve well in water; they’re two very different kinds of molecules. H2O is strongly polar, with one side positively charged and another side negatively charged. That’s why water dissolves salt so well - it splits the salts into ions and the positive ions attract the negative side of the water molecule and vice-versa. Oxygen is a non-polar, covalently bonded molecule, with no strong charge on either side. Therefore, oxygen does not dissolve well in water - there isn’t enough oxygen in water for my lungs to work if you fill them with water; I drown. However, there is a tiny bit of oxygen that will dissolve in the liquid. This amount of oxygen is much less concentrated than in the air, but animal life has figured out how to use it (hence: fish exist). Small amounts of non-polar molecules will still dissolve in a solution of polar molecules like water. To simplify a bit, this comes down to entropy; there is an energy benefit to having a tiny bit of other “stuff” dissolved in a solution rather than having a pure solution because it increases the entropy of the system. So, oxygen does dissolve in water even though it doesn’t fit in there chemically, and that’s enough for fish to exist.
Now turn that around and we have the answer to your question. Liquid oxygen would remain a non-polar molecule even while in the liquid state. Even though H2O is solid under conditions where LOX is stable, some tiny amount of H2O would still be able to dissolve in liquid oxygen for exactly the same reason; entropy. However, it wouldn’t be very much, they’d remain mostly two distinct phases, just as oxygen vapor and H2O liquid remain two distinct phases due to their chemistry.
Net veining
When a magma that has mostly cooled and crystallised in the depths of the crust is intruded by another pulse of molten rock of different composition, interesting patterns can result. The original darker silica poor rock (a basalt or an andesite) was cold enough to react to the increased pressure by shattering rather than deforming, probably along planes of weakness formed by contraction during cooling. The silica rich light coloured magma then flowed into the cracks, holding them open and widening them before freezing there as the new pulse died out.
Loz
Image credit: British Geological Survey
Instant. Natural. Volcanic. Geyser.
Thermodynamics
This metamorphic rock is extremely useful to find in the field as it catches a chemical reaction in progress. The pale blue mineral is kyanite and the pink mineral is andalusite, both polymorphs of aluminosilicate minerals. These minerals have the exact same chemical formula and will turn from one to the other depending on the pressure and temperature conditions. Kyanite generally is found at higher pressures than andalusite, while andalusite is found at lower pressures and generally higher temperatures (the third polymorph, sillimanite, forms at the highest temperatures).
If you look closely there are even single grains with pink at one end and blue at the other. This rock preserves conditions just after it crossed the boundary in pressure-temperature where kyanite reacts to form andalusite. The picture owner describes the kyanite as turning into andalusite, suggesting that the rocks were being metamorphosed to conditions where kyanite was stable and then pressure dropped; the reaction therefore literally tracks how the pressure and temperature of the rock changed during metamorphism.
This rock was found on the Isle of Mull, Scotland.
-JBB
Image credit: Anne Burgess http://www.geograph.org.uk/photo/2982832
Heat pulse from 2011 Tohoku earthquake found
A year after the Tohoku great earthquake off the coast of Japan (http://tinyurl.com/lze4l5d), a drilling vessel went to sea on a project called JFast.
The task was simple; go out after the Earthquake, drill deeper into the ocean floor than anyone had ever drilled before, sample the fault itself, install sensors, leave them there for a year, retrieve them in another cruise without having them damaged by the fault or a landslide, and try to measure a heat pulse in the fault that no one had ever successfully measured before.
Ok, maybe not that simple.
For understanding the behavior of faults, this data really is important. Earthquakes should generate heat from friction. Everyday behavior illustrates this property; just rub sandpaper up against something and it will start heating up. But prior to now, no one had ever successfully measured the heat generated along a fault, despite repeated efforts to do so.
The heat generated on a fault is an important parameter to understand because it gives information about the friction on the fault. Friction is the force that resists motion, so it is the force that keeps a fault locked, and it is the force that must be overcome for an earthquake to start and to expand. The fact that the heat from a fault had never been measured meant that scientists who wanted to understand how earthquakes start and expand had to do so with virtually no data on the fault itself.
The cruise to install the sensors took place in 2012 and they were successfully recovered a few weeks ago. Here you see members of the drilling team examining part of the core in 2012; there is a story in the article linked below of how the Japanese crewmembers of the boat were actually able to see and touch part of the fault which devastated their country in 2011. That was something of a humbling read.
Finally, the temperature data is now available, and success! A whopping 0.5°C temperature anomaly was measured due to the 2011 earthquake. You might think “that doesn’t sound like much”. You’d be correct.
Fault models since the 1970’s have used a generally-agreed upon number for the friction on a fault during an earthquake, but that number had never been measured. The researchers took this data, projected back in time to when the earthquake happened, and produced an estimate of the friction necessary to produce that heat. The friction on this fault was an order of magnitude less than has been used in virtually every fault model for 40 years, and this low friction might well be why no one has ever pulled off this measurement before.
This low coefficient of friction suggests that during an earthquake, or at least during a large earthquake, the fault begins to slide easier than would be predicted just from rocks grinding against each other. Something must lubricate the fault; allow it to slide easier than predicted from the models. One obvious candidate is clay minerals trapped in the fault surface; clay minerals hold water that can be released by rapid heating, water which could serve to lubricate a fault during an earthquake.
Researchers now are moving to the laboratory and computers to try to simulate the properties actually observed. Thanks to this data, collected from the fault that created the 2011 disaster, we’ll hopefully wind up understanding vastly more about how faults operate and what happens when one of them begins moving.
-JBB
Image credit: JAMSTEC/JFAST project website: http://www.jamstec.go.jp/chikyu/exp343/e/gallery.html
Update from Nature: http://blogs.nature.com/news/2013/05/seismic-faults-temperature-implies-deadly-earthquake-involved-low-friction.html
Update from AGU: http://blogs.agu.org/geospace/2013/06/04/return-to-tohoku-taking-a-big-quakes-temperature/
