Geology, Earthquakes & Volcanism News and Discussions

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As we continue to assess the impact of the recent eruption near Tonga, conclusions are being reached about the separate and distinct 2018 Anak Krakatau eruption in Indonesia.

Study finds that Island Collapse that Trigged Tsunami Could Not Have Been Predicted
by Sabrina Canfield
January 14, 2022

https://www.courthousenews.com/island-c ... udy-finds/

Introduction:
(Courthouse News) — Indonesia’s 2018 Anak Krakatau volcanic eruption is not what caused large portions of the southwestern side of the island to collapse, according to new research.

The collapse was instead caused by a long-term destabilizing process and not any distinct changes in the magmatic system that might have been detected by current monitoring techniques, according to a study published Friday evening in the journal Earth and Planetary Science Letters.

“This type of volcanic hazard is rare, extremely hard to predict and often devastating,” Sebastian Watt, a professor in the University of Birmingham’s School of Geography, Earth and Environmental Sciences, and senior author on the paper, said in a statement.

“Our findings show that, although there was a dramatic, explosive eruption after the collapse of Anuk Krakatau, this was triggered by the landslide releasing pressure on the magma system – like a champagne cork popping,” Watt explained.

One important next step following the report, researchers say, is the development of non-seismic tsunami detection to predict rare instances of tsunamis that are the result of external rather than internal forces, such as the 2018 Indonesian tsunami.
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What Causes a Tsunami? An Ocean Scientist Explains the Physics of These Destructive Waves
by Sally Warner

https://theconversation.com/what-causes ... ves-175213

Introduction:
(The Conversation) Tsunamis are created…(w)hen an underwater earthquake, volcanic eruption or landslide displaces a large amount of water…(T)hat energy has to go somewhere – so it generates a series of waves. Unlike wind-driven waves where the energy is confined to the upper layer of the ocean, the energy in a series of tsunami waves extends throughout the entire depth of the ocean. Additionally, a lot more water is displaced than in a wind-driven wave.

Imagine the difference in the waves that are created if you were to blow on the surface of a swimming pool compared to the waves that are created when someone jumps in with a big cannonball dive. The cannonball dive displaces a lot more water than blowing on the surface, so it creates a much bigger set of waves.

Earthquakes can easily move huge amounts of water and cause dangerous tsunamis. Same with large undersea landslides. In the case of the Tonga tsunami, the massive explosion of the volcano displaced the water. Some scientists are speculating that the eruption also caused an undersea landslide that contributed to the large amount of displaced water. Future research will help confirm whether this is true or not.
….
In the open ocean, tsunami waves can be small and may even be undetectable by a boat at the surface. But as the tsunami approaches land, the ocean gets progressively shallower and all the wave energy that extended thousands of feet to the bottom of the deep ocean gets compressed. The displaced water needs to go somewhere. The only place to go is up, so the waves get taller and taller as they approach shore.

When tsunamis get to shore, they often do not crest and break like a typical ocean wave. Instead, they are more like a large wall of water that can inundate land near the coast. It is as if sea level were to suddenly rise by a few feet or more. This can cause flooding and very strong currents that can easily sweep people, cars and buildings away.
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Tonga volcano: Plume reached half-way to space

54 minutes ago

An indicator of the great power of last Saturday's volcanic eruption in Tonga is the height reached by its plume.

UK scientists examining weather satellite data calculate it to be around 55km (35 miles) above the Earth's surface.

This is at the boundary of the stratosphere and mesosphere layers in the atmosphere.

Dr Simon Proud, from Oxford University, said these were "unheard-of altitudes" for a volcanic plume.

The most powerful eruption in the second half of the 20th Century came from Mount Pinatubo in 1991. Its plume is thought to have climbed to roughly 40km.

https://www.bbc.co.uk/news/science-environment-60088413


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Credit: TONGA GEOLOGICAL SERVICES
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The explosive volcanic eruption in Tonga on Saturday appears to dwarf the largest nuclear detonations ever conducted, according to a global group that monitors for atomic testing.

The shock wave from the blast was so powerful that it was detected as far away as Antarctica, says Ronan Le Bras, a geophysicist with the Comprehensive Nuclear-Test-Ban Treaty Organization in Vienna, Austria, which oversees an international network of remote monitoring stations.

In total, 53 detectors around planet Earth heard the low-frequency boom from the explosion as it traveled through the atmosphere. It was the loudest event the network had detected in more than 20 years of operation, according to Le Bras.

"Every single station picked it up," he says. "It's the biggest thing that we've ever seen."

As large as the explosion was, it was not nuclear in any way, Le Bras adds. Radioactive fallout, the telltale sign of a true nuclear explosion, was not detected at any station.
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The Earth's Insides May be Cooling Faster Than Previously Thought
by Peter Ruego
January 19, 2022

https://www.futurity.org/earth-cooling- ... e-2683732/

Introduction:
(Futurity) Researchers suspect that the Earth’s heat may dissipate sooner than previously thought.

The researchers have come to this conclusion after showing in the lab how well a mineral common at the boundary between the Earth’s core and mantle conducts heat.

The evolution of our Earth is the story of its cooling: 4.5 billion years ago, extreme temperatures prevailed on the surface of the young Earth, and it was covered by a deep ocean of magma. Over millions of years, the planet’s surface cooled to form a brittle crust. However, the enormous thermal energy emanating from the Earth’s interior set dynamic processes in motion, such as mantle convection, plate tectonics, and volcanism.

Still unanswered, though, are the questions of how fast the Earth cooled and how long it might take for this ongoing cooling to bring the aforementioned heat-driven processes to a halt.

One possible answer may lie in the thermal conductivity of the minerals that form the boundary between the Earth’s core and mantle.
The research results appear in Earth and Planetary Science Letters: https://www.sciencedirect.com/science/a ... via%3Dihub
Here is an abstract from that article:
(Via Science Direct) The Earth has been releasing vast amounts of heat from deep Earth's interior to the surface since its formation, which primarily drives mantle convection and a number of tectonic activities. In this heat transport process the core-mantle boundary where hot molten core is in direct contact with solid-state mantle minerals has played an essential role to transfer thermal energies of the core to the overlying mantle. Although the dominant heat transfer mechanisms at the lowermost mantle is believed to be both conduction and radiation of the primary lowermost mantle mineral, bridgmanite, the radiative thermal conductivity of bridgmanite has so far been poorly constrained. Here we revealed the radiative thermal conductivity of bridgmanite at core-mantle boundary is substantially high approaching to ∼5.3±1.2 W/mK based on newly established optical absorption measurement of single-crystal bridgmanite performed in-situ under corresponding deep lower mantle conditions. We found the bulk thermal conductivity at core-mantle boundary becomes ∼1.5 times higher than the conventionally assumed value, which supports higher heat flow from core, hence more vigorous mantle convection than expected. Results suggest the mantle is much more efficiently cooled, which would ultimately weaken many tectonic activities driven by the mantle convection more rapidly than expected from conventionally believed thermal conduction behavior.
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Sensor breakthrough paves way for groundbreaking map of world under Earth surface
https://phys.org/news/2022-02-sensor-br ... world.html
by University of Birmingham
An object hidden below ground has been located using quantum technology—a long-awaited milestone with profound implications for industry, human knowledge and national security.

University of Birmingham researchers from the UK National Quantum Technology Hub in Sensors and Timing have reported their achievement in Nature. It is the first in the world for a quantum gravity gradiometer outside of laboratory conditions.

The quantum gravity gradiometer, which was developed under a contract for the Ministry of Defense and in the UKRI-funded Gravity Pioneer project, was used to find a tunnel buried outdoors in real-world conditions one meter below the ground surface. It wins an international race to take the technology outside.

The sensor works by detecting variations in microgravity using the principles of quantum physics, which is based on manipulating nature at the sub-molecular level.
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New Model May Improve San Francisco Bay Area Seismic Hazard Maps
February 25, 2022

https://www.eurekalert.org/news-releases/944527

Introduction:
(EurekAlert) The Santa Cruz Mountains define the geography of the Bay Area south of San Francisco, protecting the peninsula from the Pacific Ocean’s cold marine layer and forming the region’s notorious microclimates. The range also represents the perils of living in Silicon Valley: earthquakes along the San Andreas fault.

In bursts that last seconds to minutes, earthquakes have moved the region’s surface meters at a time. But researchers have never been able to reconcile the quick release of the Earth’s stress and the bending of the Earth’s crust over years with the formation of mountain ranges over millions of years. Now, by combining geological, geophysical, geochemical and satellite data, geologists have created a 3D tectonic model that resolves these timescales.

The research, which appears in Science Advances Feb. 25, reveals that more mountain building happens in the period between large earthquakes along the San Andreas Fault, rather than during the quakes themselves. The findings may be used to improve local seismic hazard maps.

“This project focused on linking ground motions associated with earthquakes with the uplift of mountain ranges over millions of years to paint a full picture of what the hazard might actually look like in the Bay Area,” said lead study author Curtis Baden, a PhD student in geological sciences at Stanford University’s School of Earth, Energy & Environmental Sciences (Stanford Earth).

Bending and breaking

Geologists estimate the Santa Cruz Mountains started to uplift from sea level about four million years ago, forming as the result of compression around a bend in the San Andreas fault. The fault marks the boundary between the Pacific Plate and the North American Plate, which shift past each other horizontally in a strike-slip motion.
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Drifting Apart: New Study in Earth Science Frontiers Explains the Driving Force Behind Continental Drift
February 28, 2022

https://www.eurekalert.org/news-releases/944806

Introduction:
(EurekAlert) The breakup of the South Atlantic region, which led to the separation of the African and South American continents, is a well-known global phenomenon. In fact, the famous continental drift theory put forth by the German climatologist, Alfred Wegener, is based on the South Atlantic breakup. According to this theory, the continental plate floats on the oceanic crust and, powered by the Earth’s rotation and tidal energy, drifts relative to it. However, the driving forces behind these continental plate movements have not been fully ascertained and continue to be a topic of debate.

Specifically, none of the multiple hypotheses put forth can reasonably account for the formation of numerous linear ridges with continental fragments floating in the Atlantic Ocean. Moreover, these hypotheses do not explain why the opening of the Atlantic Ocean is wider in the south than in the middle.

Now, in a new study, researchers from China seem to have finally solved the conundrum. The team comprising Dr. Liang Guanghe from Chinese Academy of Sciences and Prof. Yang Weiran from China University of Geosciences have proposed a new dynamic model that suggests that while thermal energy can cause the continental plates to drift, the main driving force is supplied by a gravitational slip of the continental crust and hot mantle upwelling. One can picture this better by imagining a slab of butter floating a hot pan, which can move in any direction by itself. This paper was made available online on 07 January, 2022 and was published in Volume 29 Issue 1 of the journal Earth Science Frontiers* in January 2022.

How did the duo accomplish this feat? To start with, they studied two deep seismic reflection survey profiles across the Atlantic Ocean, and calculated the magnitude of crustal gravitational slip shear force in the African continent along Moho (the boundary layer between the earth’s crust and mantle), in two passive continental margin basins.

…the gravitational slip force is the main driver, and the slip only occurs on the Moho surface due to the greater thickness of the continental crust as compared to that of the oceanic crust, causing the drift to produce an even greater gravity slip.
*http://www.earthsciencefrontiers.net.cn ... 1.12.27-en
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A slow-motion section of the San Andreas fault may not be so harmless after all
https://phys.org/news/2022-02-slow-moti ... fault.html
by Columbia Climate School
Most people have heard about the San Andreas Fault. It's the 800-mile-long monster that cleaves California from south to north, as two tectonic plates slowly grind against each other, threatening to produce big earthquakes.

Lesser known is the fact that the San Andreas comprises three major sections that can move independently. In all three, the plates are trying to move past each other in opposing directions, like two hands rubbing against each other. In the southern and the northern sections, the plates are locked much of the time—stuck together in a dangerous, immobile embrace. This causes stresses to build over years, decades or centuries. Finally a breaking point comes; the two sides lurch past each other violently, and there is an earthquake. However in the central section, which separates the other two, the plates slip past each other at a pleasant, steady 26 millimeters or so each year. This prevents stresses from building, and there are no big quakes. This is called aseismic creep.

At least that is the story most scientists have been telling so far. Now, a study of rocks drilled from nearly 2 miles under the surface suggests that the central section has hosted many major earthquakes, including some that could have been fairly recent. The study, which uses new chemical-analysis methods to gage the heating of rocks during prehistoric quakes, just appeared in the online edition of the journal Geology.
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