mid ocean ridge

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Want to check out an active mid-ocean ridge? The University of Washington has a series of geophysical monitoring stations on the Juan de Fuca ridge off the Pacific Northwest US Coastline. In 2015 they were able to track a series of eruptions due to the presence of earthquakes and other seismic signals. Here you can travel along the ocean floor as they pick up the equipment on that ridge - lots of pillow basalts erupted underwater and a bunch of organisms living off the energy supplied by these eruptions.

Unsolved Paleo Mysteries Month #02 – The Paleodictyon Problem

Paleodictyon is the name for a net-like pattern found in the marine fossil record, starting in the Late Precambrian/Early Cambrian (~541 mya). Formed from thin tubes in seafloor sediment, each element of the mesh is around 1-3cm in diameter (0.4-1.1″), with entire networks covering areas of up to a square meter (10.7ft²). Some forms also have vertical tubes connecting the mesh to the surface.

And nobody knows what it is.

These patterns have even been found on the modern day seafloor at mid-ocean ridges. Samples have been taken, DNA tests have been performed… and nothing conclusive has yet been found.

Whatever makes these patterns is alive today, but we still don’t know what it is!

There are two main hypotheses about the mysterious identity of the mesh-maker. It might be some sort of small worm-like animal excavating burrows, engineering water flow through the tubes to collect food. Or the whole mesh might be the body imprint of a single creature – either a sponge or a giant foraminiferan.

Hopefully one day somebody will finally catch the Paleodictyon culprit in the act.

2

The birth and death of a tectonic plate

Geophysicist Zachary Eilon developed a new technique to investigate the underwater volcanoes that produce Earth’s tectonic plates


Several hundred miles off the Pacific Northwest coast, a small tectonic plate called the Juan de Fuca is slowly sliding under the North American continent. This subduction has created a collision zone with the potential to generate huge earthquakes and accompanying tsunamis, which happen when faulted rock abruptly shoves the ocean out of its way.

In fact, this region represents the single greatest geophysical hazard to the continental United States; quakes centered here could register as hundreds of times more damaging than even a big temblor on the San Andreas Fault. Not surprisingly, scientists are interested in understanding as much as they can about the Juan de Fuca Plate.

This microplate is “born” just 300 miles off the coast, at a long range of underwater volcanoes that produce new crust from melt generated deep below. Part of the global mid-ocean ridge system that encircles the planet, these regions generate 70 percent of the Earth’s tectonic plates. However, because the chains of volcanoes lie more than a mile beneath the sea surface, scientists know surprisingly little about them.

UC Santa Barbara geophysicist Zachary Eilon and his co-author Geoff Abers at Cornell University have conducted new research – using a novel measurement technique – that has revealed a strong signal of seismic attenuation or energy loss at the mid-ocean ridge where the Juan de Fuca Plate is created. The researchers’ attenuation data imply that molten rock here is found even deeper within the Earth than scientists had previously thought. This in turn helps scientists understand the processes by which Earth’s tectonic plates are built, as well as the deep plumbing of volcanic systems. The results of the work appear in the journal Science Advances.

“We’ve never had the ability to measure attenuation this way at a mid-ocean ridge before, and the magnitude of the signal tells us that it can’t be explained by shallow structure,” said Eilon, an assistant professor in UCSB’s Department of Earth Science. “Whatever is down there causing all this seismic energy to be lost extends really deep, at least 200 kilometers beneath the surface. That’s unexpected, because we think of the processes that give rise to this – particularly the effect of melting beneath the surface – as being shallow, confined to 60 km or less.”

According to Eilon’s calculations, the narrow strip underneath the mid-ocean ridge, where hot rock wells up to generate the Juan de Fuca Plate, has very high attenuation. In fact, its levels are as high as scientists have seen anywhere on the planet. His findings also suggest that the plate is cooling faster than expected, which affects the friction at the collision zone and the resulting size of any potential megaquake.

Seismic waves begin at an earthquake and radiate away from it. As they disperse, they lose energy. Some of that loss is simply due to spreading out, but another parameter also affects energy loss. Called the quality factor, it essentially describes how squishy the Earth is, Eilon said. He used the analogy of a bell to explain how the quality factor works.

“If I were to give you a well-made bell and you were to strike it once, it would ring for a long time,” he explained. “That’s because very little of the energy is actually being lost with each oscillation as the bell rings. That’s very low attenuation, very high quality. But if I give you a poorly made bell and you strike it once, the oscillations will die out very quickly. That’s high attenuation, low quality.”

Eilon looked at the way different frequencies of seismic waves attenuated at different rates. “We looked not only at how much energy is lost but also at the different amounts by which various frequencies are delayed,” he explained. “This new, more robust way of measuring attenuation is a breakthrough that can be applied in other systems around the world.

"Attenuation is a very hard thing to measure, which is why a lot of people ignore it,” Eilon added. “But it gives us a huge amount of new information about the Earth’s interior that we wouldn’t have otherwise.”

Next year, Eilon will be part of an international effort to instrument large unexplored swaths of the Pacific with ocean bottom seismometers. Once that data has been collected, he will apply the techniques he developed on the Juan de Fuca in the hope of learning more about what lies beneath the seafloor in the old oceans, where mysterious undulations in the Earth’s gravity field have been measured.

“These new ocean bottom data, which are really coming out of technological advances in the instrumentation community, will give us new abilities to see through the ocean floor,” Eilon said. “This is huge because 70 percent of the Earth’s surface is covered by water and we’ve largely been blind to it – until now.

"The Pacific Northwest project was an incredibly ambitious community experiment,” he said. “Just imagine the sort of things we’ll find out once we start to put these instruments in other places.”

TOP IMAGE….Ocean-bottom seismometers aboard the R/V Welcoma were deployed in the first year of the Cascadia Initiative. Credit Dave O'Gorman

LOWER IMAGE….Map of Cascadia These are the attenuation values recorded at ocean-bottom stations. Radial spokes show individual arrivals at their incoming azimuth; central circles show averages at each station. Credit UCSB

OK SO CONCEPT:

Future-time, global warming has resulted in raised sea levels, cities are sinking, the planet is warming, etc. etc. 

Viable mines for increasingly valuable minerals and metals are becoming very rare due to increased geologic activity and human interference. 

Big, over-populated nears the coasts like New York City or Los Angeles have taken on significant amounts of water and are now considered “urban swamps”. People still live there, but major businesses and many of the wealthy are moving in-land to mountain areas or plains that are predicted to become the new, financially profitable coastline in years to come. 

Meanwhile, underwater mining colonies have formed in order to mine metal from deepsea black smokers along mid-ocean ridges. 


I don’t know where I’m going with this but like can we make aqua-punk a thing?

(Image credit: U.S. Navy)

Look at that picture and consider the question.

Why are there mountains at that part of the ocean but not in most of the others?

Hot spot? Oceanic ridge?

The answer is because that’s the only spot where a ship’s been.

72% of the Earth’s surface is below the ocean. Most of the Southern Hemisphere hasn’t been explored however and according to geophysicist Robert Ballard, “There are only ever four or five people on the ocean floor at any one time.”

People played golf on the Moon before anyone entered the single largest feature on our own planet, the Mid-Ocean Ridge which covers almost a quarter of the planet.

It’s remarkable that there are people conceiving of ways to colonize other moons and planets and yet where are all the ocean colonies?

Most of the planet doesn’t get touched by Sunlight. At the deepest parts of the oceans, sunlight cannot penetrate and yet life thrives there, living off of chemosynthesis and the heat from the Earth’s core. These same conditions could enable life on Europa and Enceladus.

The National Oceanic and Atmospheric Administration (NOAA) is America’s other exploration program (NASA’s sibling). One year of NASA’s funding (which is not a lot) could fund our entire oceanic exploration program… for 1,600 years.

Earth is a planet in space. It would do us well to remember this. There’s still so much to learn from our mother planet, why spurn these valuable lessons?

2

Pangaea Ultima is a possible future supercontinent configuration. Consistent with the supercontinent cycle, Pangaea Ultima could occur within the next 250 million years.

Supercontinents describe the merger of all, or nearly all, of the Earth’s landmass into a single contiguous continent. In the Pangaea Ultima scenario, subduction at the western Atlantic, east of the Americas, leads to the subduction of the Atlantic mid-ocean ridge followed by subduction destroying the Atlantic and Indian basin, causing the Atlantic and Indian Oceans to close, bringing the Americas back together with Africa and Europe. As with most supercontinents, the interior of Pangaea Proxima would probably become a semi-arid desert prone to extreme temperatures. [x][x][x]

(more at @annotated-hetalia)

Marie Tharp and the Mid-Atlantic Ridge

In honor of International Women’s Day and the beginning of Women’s History Month, we thought some of our favorite female geologists deserved a shout out. One of my personal favorites is this girl, Marie Tharp, who did something very important for our modern understanding of geology—she discovered the Mid-Atlantic Ridge.

anonymous asked:

What do you think about the controversy regarding the origin of intraplate volcanism (i.e.: whether it is caused by deep mantle effects such as plumes or through shallow mantle effects such as the plate model, as proposed by Gillian Foulger, Don Anderson and others)

The person who runs this blog is an igneous petrologist with a particular interest in the mantle, so you’re going to get my perspective on how I think the mantle works.

First and foremost, I am a believer in plumes. It’s actually a common thing we see in any fluid heated from below - you can even do experiments in simple fluid containing tanks and they are readily generated. 


A mantle plume is a blob of low-density, usually hot material rising up from the bottom of the mantle to at least the transition zone, but most likely up until it reaches the crust. When it does that, it would carry heat and whatever the material of the lower mantle is up with it. 

The complexity comes from the fact that we’ve never sampled the mantle, nor have we ever sampled a mantle plume directly, so we can’t physically walk out in the field and find a mantle plume to map. Instead, we see possible results of these plumes at the surface; large igneous provinces like the Ontong-Java Plateau, the Columbia River Basalts, or the Siberian Traps could be the heat from these plumes arriving and melting the other rocks near the surface to generate magma.

These plumes also tend to have long tails, like you see in that image, which could allow additional hot material to flux up to the surface even after the plume head is gone. These tails could be the type of feature that feeds hotspots such as Hawaii, Iceland, and Yellowstone that continue activity for hundreds of millions of years after the plume head has moved away.

Overall I think the evidence that these things exist is strong. You can recognize distinct compositions in the rocks that do not fit well with originating in the same mantle tapped at mid-ocean ridges where the crust breaks randomly, you can recognize that huge amounts of additional heat are required to produce something like Ontong-Java, and today even seismic instruments are starting to detect hot zones beneath places like Iceland and Yellowstone which likely represent the plume conduits. 

Now that I’ve given my prejudice and logic, let’s say a few words about the late Don Anderson, who died earlier this year. 


I did my graduate work at the same institution as Don Anderson and so got to hear a good amount of discussion of his ideas. Dr. Don Anderson was a seismologist who was extremely skeptical of the Plume model for the origin of Hawaii/Large Igneous Provinces. He built the website mantleplumes.org which is a clearinghouse for discussion of the merits and demerits of the existence of plumes. 

The main alternative to explaining mantle plumes is that plates as we understand them aren’t rigid, they twist and break in funny ways that as a consequence can allow large amounts of molten rock to come up to the surface. They have presented these models in several formats, including arguments regarding how the chemistry of “plume” magmas could be generated in the upper mantle and what kinds of seismic evidence would be produced in those cases.

In general I have found those arguments unconvincing. I’m a geochemist so focusing on those - they rely on processes I believe are much better fit with the plume model. Our best temperature estimates suggest that magmas from Iceland and Hawaii are in fact generated by abnormally hot mantle and our chemical evidence argues that many of the signatures in these locations are produced by material that has been in the mantle for billions of years, which would not be very likely IMO if plumes were simply cracks in the crust that tapped the upper mantle. When we tap the upper mantle we get something like mid-ocean ridge basalts, when we tap the lower mantle we get a much greater diversity of magmatic compositions. 

On top of that, as the quality of seismic images have improved, we’ve gotten much better at distinguishing hot zones that could be plume conduits. Plumes would be small, <100 km wide, so they’re hard for seismic techniques to detect, but we’re getting there. Here’s a possible seismic image of the Yellowstone plume conduit:  


So, I think the evidence is good that there are mantle plumes that carry up hot, old material from deep in the mantle, and we’re getting better at understanding these with time.

However, although I disagreed with Dr. Anderson and colleagues, I want to take a minute to stress the important role they play. All scientists like fitting things into simple models, and so if we can come up with a plume model that explains Iceland and Hawaii, we might just call it a day. The importance of people like Dr. Anderson to me is reminding me that it’s never that simple.

We have a plume tail model that works for Iceland, Hawaii, and Yellowstone, with volcanoes that gradually get older farther away from the Hotspot, but if we go to the Western Pacific, that setup totally falls apart. The Western Pacific is filled with seamounts that have hotspot-like chemistries but where the order is lacking.

That means something fundamentally different is happening here. Our simple plume model doesn’t do a good job of explaining a lot of things that happen on Earth, even though the chemistry of these rocks fits with coming from the lower mantle. Why aren’t they organized like Hawaii? Does that mean there are multiple types of plumes?

Dr. Anderson would reply that once we start needing 4-5 different types of plumes to explain all the different features, our plume model is breaking down and in that he’s right. No simple plume model explains all the hotspot-like features we see on Earth. Even if plumes best fit the chemistry, there’s a lot of work to do to understand what really is happening. Is there some general feature that can explain both Hawaii and these features, something related to the LLSVP discovered in the lower mantle?  Why does one spot get one type of plume while another gets a different signature? These are great questions and its required of those who like the plume model that we need to explain them. That’s the reason I liked hearing Dr. Anderson speak sometimes; even though most petrologists don’t agree with his interpretations, it’s extremely important to challenge basic assumptions and models so that they really do find the best ways to explain the data we have.

People who work on the mantle are doing a tough job. We’re trying to take tiny bits that melted out of the mantle, criscrossed the entire crust, and got up to the surface, and use those dregs to figure out an entire planet. It’s very important to make sure we don’t get lost in our own assumptions and that as techniques and measurements evolve we keep stepping back and make sure that our assumptions still hold. That’s a lesson I personally picked up from Dr. Anderson and I hope it’s a good one to share. 

  • ward: skye?
  • skye: yes?
  • ward: you were a seismic change
  • skye: oh god
  • ward: and i know the whole hydra thing created a very deep trench in our relationship
  • skye: somebody stop him
  • ward: but i know that it doesn't fault easily
  • skye: grant
  • ward: and just as lava fills the gap in a mid oceanic ridge
  • skye: grant pls
  • ward: i will fill the trench in your heart with love the size of the himalayas
  • skye: dad help
  • ward: you will be my focus and i will be your epicenter
  • skye: wut
  • ward: foci are perpendicular to epicenters
  • skye: pls kill me
  • ward: and as sudden and groundbreaking this is
  • skye: oh god get on with it
  • ward: will you marry me
  • skye: excuse me
  • ward: my hot spot can make a lot of baby volcanoes

This globe shows the age of the rocks that make up the seafloor of the Atlantic Ocean. The youngest rocks can be found around the Mid-Atlantic ridge (shown in red). The Mid Atlantic ridge is essentially a submarine mountain range which is the result of sea floor spreading; molten lava pours out and hardens into basalt rock. Plate tectonics gradually moves the rocky seafloor away from the ridge and hence the rocks get older. The oldest rocks in the Atlantic are about 180 million years old.

-Jean

Image courtesy of NOAA

vimeo

If the first frame of this video, saying “Why Iceland” and answering it at the same time, doesn’t get you to click I don’t know what to do.