#geohazard

[bettergeology]

Keeping an eye out

Mount St. Helens is the most active volcano in the Cascades. It's major eruption in 1980 has been succeeded by about 10 other smaller eruptions and maintains near-constant microseismicity. The first pictures show one of the close-in monitoring stations at Windy Ridge. The USGS Cascade Volcano Observatory maintains a number of large monitoring stations close to the mountain, near the vent, where they've been armored to protect from eruptive activity. These stations typically include a seismometer (seismogram here), a GPS station (the white dome), and other equipment like geophones or a webcam. Volcanoes never erupt spontaneously, they are always preceded by some kind of activity - usually small earthquakes - and let you know when they're ready to go. St. Helens hasn't done anything since about 2010, taking a well-deserved rest after the major lava dome growth in 2004-2008.

Around the mountain to the southeast, you can hike through the Plains of Abraham's pumice fields and past the slot-canyon head of Ape Canyon to the rim of the Muddy River, where another monitoring station reports seismicity and GPS data. The GPS stations observe the shape of the volcano over time. As gas, fluids, and magma move around inside the mountain, the surface deforms. Rapid or dramatic deformation is often indicative of impending eruption or other activity, and is one of the most important parameters in the volcanologists' arsenal.

[earthstory]

Vesuvius, the serial killer

Natural disasters dominate our headlines. Body counts soar and it can make us feel like unwelcomed guests on an increasingly hostile planet. Nowhere is the peril more apparent than in the shadow of a volcano.

The Earth is home to some 600+ active volcanoes; half a billion people live within their blast range. Some are known killers. Montserrat in the Caribbean, the 1997 eruption buried the nations capital in ash. Mount Pinatubo in the Philippines, its 1991 blast was 10 times the size of Mount St. Helens. Active volcanoes can appear dormant, but many are in fact ticking time bombs. Naples Italy, the uneasy neighbour of a seismic serial killer, makes it one city most likely to suffer a fiery death. Here 600,000 people live within the red zone. That’s the blast range of what’s undoubtedly the worlds most treacherous volcano: Vesuvius, a killer with a rap sheet a mile long. Its historic eruption in 79 AD entombed two entire cities, Pompeii and Herculaneum, each about as close to Vesuvius as downtown Naples. Their victims are a haunting reminder of an ancient disaster and a warming to Naples population today.

While most of the world knows the story of Pompeii, few realise just how often Vesuvius erupts. The last time was little more than a half a century ago in 1944. The allied forces had invaded Italy and were driving north; a few tremours from a quiet volcano was the last thing on their minds. For more than a week pumice, volcanic gases and searing hot ash shot out. Rivers of lava poured down the mountainside. In total it killed 26 people, the city got off easy. Which is why perhaps its lesson was seemingly ignored. Because from 1994 to 2004, those living in Vesuvius’s shadow grew to 600,000, and all the while this mass murderer is in no doubt building towards another disaster.

The city is so concerned; they’re actually paying people to leave. Officials are pleading with families to move out of the red zone, the area most likely to be devastated by the next eruption. Why haven’t people already left? Because Vesuvius like many other volcanoes that go long periods between eruptions holds a deadly attraction. Mineral rich volcanic soil creates an inviting paradise on the outside, beneath, murder broods in its molten heart.

Like Earthquakes, most active volcanoes are born from the ‘rubbing’ of tectonic plates, which brings up magma from deep beneath the Earth. Some of the volcanoes in the middle of plates aren’t as volatile. They continuously spew lava leaving the underground pressure. It is this action that somewhat stabilises the Earth. If it didn’t realise this built up pressure, it would eventually go off with one mighty bang and make Earth inhabitable for human life. Volcanoes on vaults like Vesuvius build magma and pressure for years until they erupt with explosive force.

A force of nature that’s impossible to stop. It isn’t a question of if it will happen, but when it will happen.

~ JM

Image Credit: http://bit.ly/1GGHIts

More Info: Living in the Red Zone http://bit.ly/1wJkPmY

Vesuvius Introduction: http://bit.ly/1tmqHNJ

Mount Vesuvius, ticking time bomb:http://bbc.in/1EpVdyg

BBC News Report Video: http://bbc.in/1NtQVp7

[earthstory]

THE ARKSTORM COMETH

Once upon a time, Central Valley of California became a lake when it was flooded in what is termed an “Arkstorm.” Yes, that’s right, a storm huge enough to require an Ark to survive.

Though this name “ARkstorm” brings about mental images of Noah and all the animals lining up to board an oversized wooden barge, the initial letters “AR” stand for “Atmospheric River.” An atmospheric river is a swath of water vapor-rich atmosphere that can stretch for thousands of kilometers. To paraphrase F.M. Ralph, it’s an airborne river flowing toward you at 30 miles per hour that contains more water than 7–15 Mississippi Rivers combined. In the case of California, an atmospheric river can begin in the tropics of the South Pacific, then flow east all the way to the coast, trapped within atmospheric layers.

Imagine this river hitting the mountains of California, head-on. That is when an Arkstorm occurs, causing massive flooding. In the flood of 1861-1862, Los Angeles received 1.65 meters (66 inches) of rain, and the Central Valley became a Central Sea reaching a depth of more than ten meters with flooding conditions lasting for six months. Geologic studies show that these sorts of mega-floods happen once every one hundred or two hundred years in California, with or without the aid of global warming.

Global warming? With rising temperatures, there will be more water vapor in the atmosphere, and (as for mega-hurricanes) a higher chance for the formation of the kind of atmospheric river that can cause a super storm. If you don’t live in California, don’t feel left out: atmospheric rivers can emanate from the Gulf of Mexico and cause deluges in Tennessee, or in the South Atlantic and pour out over Britain and the rest of Europe.

Today, the California Department of Water Resources (http://www.water.ca.gov/floodmgmt/) hopes that their dams and levees can control this kind of flood, but the system has yet to be tested by a real Arkstorm.

Perhaps in the future of our climate-confused world, California will be drowning.

Annie R

A previous post of ours about "Atmospheric rivers" hitting California: http://tmblr.co/Zyv2Js_P34XM

[earthstory]

Planning for a tsunami

Off the coast of Oregon and Washington, a piece of ocean crust known as the Juan de Fuca plate is being pushed down into Earth’s mantle at a gigantic fault known as the Cascadia subduction zone. That fault is a megathrust, the same type of fault that produced the 2004 Indonesia tsunami and the 2011 Japan tsunami.

That fault has a long record of producing giant earthquakes and tsunami, even though there aren’t written records from many of them except possibly for the most recent one about 300 years ago. Some of those tsunami are testified to by sand layers on shore, others by parts of the land which were submerged and then re-exposed as the crust bends (http://tmblr.co/Zyv2Js1dbFv2t).

This fault has produced massive earthquakes and tsunami before and it will do so again. With the recent tsunami disasters still in mind, governments continue funding projects to better understand the hazards of tsunami waves to populated lands.

Estuaries – the open bays at the end of many large rivers – can concentrate tsunami energy. The waves get inside them and can be focused, driving water levels upward and damaging harbors and cities throughout.

This image shows a model created by scientists at Oregon State University of a tsunami wave hitting the Columbia River. You can see many places where tributary rivers that enter the estuary are at risk from flooding – as much as 4 meters along coastlines inside the estuary.

These models are extremely useful in helping planning for future tsunami impacts. The areas at greatest risk for flooding are areas that should have building codes that could allow structures to survive a large tsunami – possibly even elevation above possible wave heights. These areas also should have active evacuation and warning plans in place, in addition to drills to get people used to hearing and responding to the warnings.

These models also are useful for showing the conditions that are most hazardous. Surprisingly, the high flows on the river in the spring don’t really impact tsunami heights that much on this river. On the other hand, daily tides do. If a tsunami hits at high tide, its impact is much worse than a tsunami that hits at low tide. That information can also be used in planning responses at the time an earthquake hits and in knowing what the maximum reach of the waves could be.

-JBB

Image credit: OSU http://oregonstate.edu/ua/ncs/categories/college-engineering

https://phys.org/news/2015-02-outlines-impact-tsunami-columbia-river.html

[earthstory]

The Spire of Pelée

In 1902, Mount Pelée on the island of Martinique unleashed one of the deadliest volcanic eruptions of the 20th century. After a period of a few weeks activity, on May 8 it exploded, producing a pyroclastic flow nicknamed a nuée ardente, which translates to “glowing cloud”. Gases dissolved in the magma broke free, tearing apart the molten rock inside the volcano as it escaped. That mixture of gas and rock enveloped the city of St. Pierre below it, leaving only a handful of known survivors out of a city of 28,000.

After the climactic eruption, Mount Pelée calmed down, but later in the year it began a new phase of activity. Rocks that could be seen glowing at night began oozing out of the volcano, pushing upward and forming this spire that eventually reached over 300 meters in height. The spire grew as much as several meters per day until it finally collapsed in early 1903. While the collapse of this spire was no where near as devastating as the initial eruption, hopefully you can also imagine how collapse of a dome like this one could also be a hazard to anyone nearby.

Many volcanoes have sequences like this to their eruption: violent and explosive eruptions when the molten rock below has a high gas content, slow and oozing dome growth when gas contents are low.

-JBB

Image credit: Lacroix, A., 1904, La Montagne Pelee et ses eruptions: Paris, Masson et Cie, 622 p. http://www.geology.sdsu.edu/how_volcanoes_work/Pelee.html http://content.time.com/time/specials/packages/article/0,28804,2014572_2014574_2014625,00.html

[earthstory]

tornadotitans

What makes a wall cloud dangerous? In short: if its persistent and rotating its time to really pay attention. Watch the video for more

[earthstory]

HayWired

In Southern California, the San Andreas Fault makes up the plate boundary between the North American plate and the Pacific plate, with that single strike slip fault taking up a majority of the motion between the two plates. Northern California is a bit different. The San Andreas fault runs offshore to the west of San Francisco and it takes up part of the plate motion, but another part of the plate motion is taken up by a strike slip fault to the East, the Hayward Fault.

The Hayward Fault runs through communities to the East of San Francisco Bay, including Oakland and Berkeley, where it runs through the campus of the University of California (https://tmblr.co/Zyv2Js1Q0m6xP). Part of the Hayward fault last ruptured in a major earthquake in 1868, when there was a much smaller population than there is today. The nearby San Andreas fault segments last ruptured in the 1906 Earthquake that devastated San Francisco. Faults often don’t behave well enough to say that they will rupture every (blank) number of years, but it is absolutely certain that this fault will break again, triggering a major earthquake to the east of San Francisco Bay, in an area inhabited by millions.

To understand and prepare for this upcoming disaster, scientists have produced computer models like this one, simulating how the area around the fault will shake given a reasonable rupture along the Hayward Fault. This fault model has been nicknamed the HayWired Scenario. The colors are coded to the Mercalli scale of Earthquake intensity, which characterizes earthquakes based on how strong the shaking is at any particular spot (https://tmblr.co/Zyv2Js2BNeuY7).

You can find interesting details of how the local geology moves the energy of the quake around. Look for the extreme shaking in areas right next to the Bay; these areas are loose, water-saturated sediments and those areas typically amplify seismic shaking. Across the Bay, the Marina district in San Francisco is built on these sorts of loose sediments and it suffered heavy damage in both 1906 and 1989, in part because these sediments undergo liquefaction during quakes.

Aside from liquefaction zones, the shaking is most intense right next to the fault, and then energy is carried away by other major geologic structures. Note the slow moving clock at the upper left – a full rupture of this fault would create an earthquake lasting more than a minute.

Last week, there was a magnitude 5 earthquake off the coast of California. Scientists and engineers have developed systems that can trigger an “early warning” of several seconds, sent to smartphones and other automated devices. In California this system is only preliminary, but it has been deployed elsewhere in the world including Japan and Mexico. During the small quake last week, the early warning system gave a warning of several seconds before the strongest shaking arrived.

Several seconds isn’t a huge amount of time, but it can make a lot of difference. Trains can be slowed down, power stations can be put into safe mode, doors can be opened on fire stations to let trucks out, and people can brace. One more creative example of why only a few seconds warning could be hugely important – one southern California Geologist was apparently in the dentist’s chair at the time the shaking started. That’s not a procedure you want to be undergoing when an earthquake starts, so if your dentist can move away a few seconds in advance…that seems to be worth the cost of the program right there.

The Federal government budgeted several million dollars to begin deployment of this warning system in its 2018 budget a few weeks ago. It won’t do everything, but by this time next year there’s a good chance that smartphones in California will be able to link to this system, giving anyone who downloads the right app a chance at an Earthquake Early Warning

-JBB

Video credit/HayWired scenario (USGS)

https://wim.usgs.gov/geonarrative/safrr/haywired_vol1/

Reference:

https://lat.ms/2GXH823

[earthstory]

Ridiculous capture of a rockfall and debris flow in Switzerland, 2015