Guest Videos: Gakkel Ridge Volcanoes

Gakkel Rise, between Greenland and Siberia, is named after the Soviet geoscientist who first mapped the Arctic Ocean’s floor. It’s a long, underwater mountain range that hosts a complex of volcanoes with delightful names like Jessica’s Hill, Duque’s Hill, Oden, Thor, and Loke (not the Marvel spellings of “Odin” and “Loki,” but the same Norse-god reference).



While at least some of these volcanoes are active, Jessica and friends sit roughly 13,000 feet (4000 meters) below sea level–too far down to influence pack ice in any way.

The last known eruption, probably in 1999, scattered debris over Oden and Loke. A 2007 remote submarine expedition also found recent pyroclastic deposits, though that is not recognized as another eruption.

These were history-making discoveries. Until then, volcanologists hadn’t known that explosive eruptions can happen at such depths (slightly below the RMS Titanic wreck’s depth), where pressure is almost 400 times that on the sea surface.



But the Gakkel Rise has always surprised scientists, at first in the 1950s by being pretty much exactly where Yakov Yakovlevich Gakkel predicted it would be found.

When the plate tectonics era dawned, this northern extension of the Mid-Atlantic Ridge–a spreading center–was considered to be nonvolcanic. However, in 1999, nuclear subs detected volcanic activity there, and today Gakkel Ridge is known to be the slowest spreading center in the world–much slower than the Mid-Atlantic Ridge, and even more of a slowpoke than the Mid-Cayman and Southwest Indian ultraslow spreading ridges.



The potential mineral wealth that he mentions at the end of the video complicates the picture. Along with untapped gas and oil deposits, it’s a major motivating factor in the Arctic territorial claims we mentioned in yesterday’s post about the namesake of nearby Lomonosov Ridge.

The area needs exploration for scientific reasons, not just for geopolitical advantages.

What little is already known about Gakkel Rise volcanism is unusual. There may even be a giant caldera there, although I have only found one reference to it. I don’t know whether that’s because it is such a new paper (2017) or because this might not be a widely accepted hypothesis yet.

Anyway, as another WordPress blogger says (in a much better post):

The Gakkel Ridge is one of the most remote tectonic regions on the planet. Yet it has volcanic activity and life. It is a spreading center that connects the active Mid Atlantic Ridge to the non-spreading Eurasian Plate. Not unexpectedly, volcanic activity is found closer to the MAR, though hydrothermal vents are found in the half of the ridge closest to Greenland and the MAR. It is home to the deepest pyroclastic activity ever observed. It also has some of the thinnest oceanic crust ever observed and may even have mantle rocks exposed to the ocean. Like all our volcanic regions, the more we look at this, the more we find things that we never expected. Which is why we do this.



Sources:

Moran, K.; Backman, J.; Brinkhuis, H.; Clemens, S. C.; and others. 2006. The Cenozoic palaeoenvironment of the Arctic Ocean. Nature, 441(7093): 601.

Nikishin, A. M.; Gaina, C.; Petrov, E. I.; Malyshev, N. A.; and Freiman, S. I. 2017. Eurasia Basin and Gakkel Ridge, Arctic Ocean: Crustal asymmetry, ultra-slow spreading and continental rifting revealed by new seismic data. Tectonophysics, via PDF.

Piskarev, A., & Elkina, D. (2017). Giant caldera in the Arctic Ocean: Evidence of the catastrophic eruptive event. Scientific Reports, 7, 46248.


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A Very Addictive Online Dinosaur Site


Between working on the ebook and keeping up with Kilauea (see “live” blog link in upper right corner of the page), I can only put up some guest videos to thank people for coming here.

However, I found this site, first with the interactive globe that shows what position the continents were in down through geologic time.

For example, you have heard that a big asteroid hit the Yucatan 65 million years ago and caused a mass extinction, right? And you picture an impact on modern-day Mexico.

But the continents were arranged somewhat differently back in the day:

Continue reading

Havre Seamount

You need this background to the recent news that, at Havre Seamount near New Zealand, scientists have found the largest deep-water silicic eruption in history. Some cool videos of eruptions are included, too.

Thanks to plate tectonics, almost three-quarters of Earth’s lava is erupted in the oceans, at mid-ocean ridges, not on the land where we can see it.

These spreading ridges, as they are called, are really a high volcanic mountain range rising from the abyssal depths and running down the middle of just about every ocean on the planet.

Most of that lava and rock is mafic – a word coined from the chemical symbols for magnesium and iron, which enrich this type of magma and make the resulting rock dark.

This runny red stuff usually erupts quietly as pillow lava, but in relatively shallow water, mixing molten rock and good old H2O can be spectacularly explosive.

That is the 1963 Surtsey eruption, off Iceland’s southern coast. This volcano sits in the middle of the Atlantic, but since it’s on a coastal shelf (and therefore atop the Mid-Atlantic Ridge, along with Iceland), ocean depth there is measured in hundreds of feet, not miles.

Even so, scientists would have had a hard time studying the eruption if it hadn’t broken through to the air.

Surtsey is made out of mafic rock. Another type of dramatic volcano comes from silicic magma – it contains a lot of silica instead of magnesium and iron.

Usually you find silicic volcanoes near the coast, as in the High Cascades of the US Pacific Northwest. They form in such places because, offshore, a seafloor plate is sinking down into the depths of the Earth and the continental plate is riding over it.

Of course, it’s hot down there in the mantle. Not only that, seawater is mixed in with the sinking rock – this lowers the melting temperature and causes chemical reactions that, among other things, make the silicic magma very sticky.

Volcanoes form wherever this magma reaches the surface near the trench made by the sinking plate edge.

The eruption may be explosive, as when gases build up a lot of pressure. Without so much gas, it can be nonexplosive but gooey, as in the Mount St. Helens eruption that began in 2004.

Here is a USGS closeup view of how Mount St. Helens rebuilt itself between 2004 and 2008:

Sometimes subduction (one tectonic plate sinking underneath another) happens far from land.

Volcanologists know this, but they haven’t been able to learn much about the resulting silicic volcanoes, since it all happens in deep water, which is technically defined as more than 500 meters, or over a third of a mile, below the surface.

The pressure of water at those depths is enough to prevent Surtsey-like blow-ups, so evidence of these eruptions usually goes unseen.

In 2012, though, volcanologists were able to trace a raft of pumice that had been sighted by satellite – see the image at the top of the page – back to Havre Seamount in the general vicinity of the Kermadec Islands.

That in itself was big news, but now technology has also enabled volcanologists to visit the volcano.

That is what all the fuss is about today!

Here is the original University of Tasmania fly-through used by Scientific American in the above video:

As of this writing, the Smithsonian doesn’t have a picture of Havre for the volcano’s GVP page. That’s going to change soon, thanks to this major volcanological success!


Featured image: Havre’s pumice raft spreads across the sea, NASA.


Sources:
Carey, R.; Adam-Soule, S.; Manga, M.; White, J. D. L.; and others. 2018. The largest deep-ocean silicic volcanic eruption of the past century. Science Advances. 4(1):e1701121.

Jakobsson, S. P.; Thors, K.; Vésteinsson, A. T.; and Ásbjörnsdóttir. 2009. Some aspects of the seafloor morphology at Surtsey volcano: The new multibeam bathymetric survey of 2007. Surtsey Research. 12:9-20.