Scientists have finally figured out what caused the largest volcanic eruption in human history

Lindsay Dodgson

Business Insider UK

Jan 27, 2017

A satellite image of Lake Toba in Indonesia. NASA Landsat


Indonesian volcano Toba produced a cataclysmic eruption that devastated the region 73,000 years ago. Monstrous volcanoes like this are called supervolcanoes, and sometimes their impacts are so huge, they can cause global climate change.

Now, scientists may have worked out what triggers them to blow in a new study published in the journal Scientific Reports.

The Toba eruption was the largest volcanic eruption witnessed in history, which covered 2,800 cubic kilometers of the surrounding area in volcanic ash, causing enormous amounts of rain in Indonesia and India.

How exactly these huge amounts of magma are created (and why they erupt so violently) has been a cause of debate between scientists for a long time. It has been known that volcanoes erupt because of density and pressure, and generally it is a way that Earth can release excess heat and pressure. Still, the precise trigger has remained a mystery.

A group of researchers at Uppsala University and their international colleagues may have found some answers lying in millimeter-sized crystals called quartz crystals embedded in the volcanic ash and rock.

Quartz crystals grow in magma, and register chemical and thermodynamical changes before an eruption, which is similar to how tree rings record climate change, according to Dr David Budd, lead author of the study from the Department of Earth Sciences at Uppsala University.

"When the conditions in the magma change, the crystals respond and produce distinct growth zones that record these changes," he said in a statement. "The problem is that each 'tree ring'-analogue is only a few micrometers across, which is why they are extremely challenging to analyse in detail."

While studying the quartz from Toba, the researchers found that there was a difference in the composition and weight of the outer part of the crystals compared to the inside. Around the outside the crystals were heavier and contained a form of oxygen called 18O. On the inside, however, there was a lighter form called 16O.

According to the study authors, the ratio suggests that something in the magmatic system had changed drastically just before the big eruption. So what happened? The researchers think that when the magma melted, it took along with it a large volume of a nearby rock which contained the same ratio.

"This rock type also often contains a lot of water, which may be released into the magma, producing steam, and thereby an increased gas pressure inside the magma chamber," said Dr Frances Deegan, another author of the study. "This rapidly increased gas pressure and eventually allowed the magma to rupture the overlying crust, and send thousands of cubic kilometres of magma into the atmosphere."

HOW OFTEN DO SUPERVOLCANOES ERUPT?



THE NYIRAGONGO VOLCANO IN VIRUNGA NATIONAL PARK.


Luckily, supervolcanoes like these erupt very infrequently. Volcanic eruptions are measured by the Volcanic Explosivity Index (VEI,) with VEI 7 and VEI 8 eruptions being the most powerful.

Other than Toba, these are some of the most massive supervolcano eruptions in history:

• La Garita Caldera erupted approximately 27,800,000 years ago, and released 5,000 cubic kilometers of magma.
• Huckleberry Ridge in Yellowstone had a bulk ejection of 2,500 cubic kilometers about 2,100,000 years ago.
• Atana Ignimbrite in Chile erupted about 4,000,000 years ago, also ejecting 2,500 cubic kilometers.
• In 1815, the Tambora volcano on Sumbawa Island in Indonesia erupted in what is considered the largest ever eruption in recorded history. It was a VEI 7 on the VEI scale, but an estimated 100,000 people died from the effects, and it caused a global volcanic winter.

Although famous, eruptions such as Mount Vesuvius (Pompeii in 79 AD) and Mount St. Helens in 1980 were very small in comparison to these supervolcanic ones.

Researchers say that Toga's eruption in particular was so colossal it came close to wiping out humanity entirely. It's a matter of when, not if, supervolcanoes erupt again. Here's to hoping that we're better prepared when the next one happens!

Our Planet Doesn’t Just Support Life, It is Also Living Vessel

Mike White

TrendinTech
February 5, 2017

Although many people don’t realize, our planet doesn’t just support life; it too is alive. If you were to strip away all of the human-made structures, and even ourselves and other living creatures, you would still see waters flowing, volcanoes erupting, and trees blowing in the wind. Tectonic plates are thought to play a part in making the planet a livable place to live, and as far as we know, Earth is the only one in the solar system known to have them.

Beyond our solar system, astronomers have found various other planets – some of which may boast plate tectonics and could well be habitable. Even of these planets don’t hold tectonics that doesn’t mean to say there’s no geological activity going on there. Both the moon and Mars experience quakes, Jupiter’s moons have volcanoes and geysers, and evidence suggests that Mercury has a molten core (at least partly) and none of those have plate tectonics.

However, plate tectonics and geological activity aren’t the same. Ours is the only planet in the solar system that has a broken outer crust with plates that extend hundreds of kilometers beneath the surface. Where these plates shift against one another, they renew the surface, and at mid-ocean ridges, plates are pushed apart by rising magma forming a new crust. These are all essential processes that need to happen for the Earth continue as it is – without them, the planet would be as uninhabitable as Venus.

Plate tectonics also help to keep volcanoes active by ensuring the carbon cycle runs efficiently. A warmer climate will produce a lot of rain which ultimately aids in the extraction of carbon dioxide from the atmosphere. Then the gas is dissolved in raindrops and splashes on the rocks where chemical reactions take place that release carbon and other minerals from them. Eventually, the water will flow back to the ocean where carbonate rocks and organic objects like seashells will form. Where the carbonate settles on the bottom of the ocean, volcanoes are activated, and carbon is sprayed back into the atmosphere as carbon dioxide.

Fresh rocks are bought to the surface with thanks to plate tectonics, mountains are formed from plate tectonics, and diverse environments have been created because of plate tectonics. Brad Foley, a geophysicist at Penn State University, said, “Plate tectonics help keep volcanism active for a long time. If we didn’t have volcanism sending back carbon dioxide into the atmosphere, then the planet could get very cold. It would freeze over.” Plate tectonics are also helpful when it comes to removing elements from rock and carrying them to sea. Without plate tectonics we wouldn’t have such diverse environments either, so we have a lot to be thankful to them for.

Another thing that wouldn’t be without the help of plate tectonics is the hydrothermal vents that lie on the ocean floor. These vents are home to various marine life, and some experts have even predicted similar events could have given rise to the first instances of life on Earth. But, the real question lies in if plate tectonics are a requirement in order for life to start and survive. Lindy Elkins-Tanton is a planetary scientist at Arizona State University, and she says, “Plate tectonics is critical for the life we know and love as humans. But, it’s not necessarily required for life in a broader sense.” Just because Earth requires plate tectonics to maintain a regular carbon cycle, that doesn’t mean a different planet has the same requirement.

However, one thing that can be agreed upon is that plate tectonics could help coax life into existence but whether that’s necessary – who knows? Elkins-Tanton says, “We don’t understand enough about plate tectonics to understand whether it’s critical for habitability.” But, to try and prove this theory by looking at other planets outside our solar system is almost impossible. “We could barely detect it on our own planet, and we’re standing right on it”, says Elkins- Tanton. So, we may never really know if plate tectonics is needed, but for now, at least, we can still believe that Earth is the only planet truly alive.

These declassified maps show how the CIA saw the world at the height of theCold War

Christopher Woody

Business Insider

Feb 2, 2017

Perhaps more so than any other tool used by the clandestine services, an accurate map can mean the difference between success and failure, or life and death.

The CIA, renowned for its secrecy, has long kept its maps and cartographic methods under wraps.

But, in honor of the agency's Cartography Center's 75th anniversary, the CIA put a number of maps online, depicting how "the company" has viewed the world since its inception in the aftermath of World War II.


Suspected sites of missiles in Cuba, 1962CIA


President Franklin Roosevelt created the agency that would eventually become the CIA in the early 1940s. The map division produced a bevy of maps vital to strategic planning during the war, according to National Geographic.

The agency's mapmakers had a broad mission, asked to produce maps and data relevant to whatever national security issues the country may have encountered. In the process, "Geographers and cartographers amassed what would be the largest collection of maps in the world."

In a sign of how valuable maps were during the Cold War, the Soviet Union dedicated a great deal of resources and time to not only making exacting maps of foreign capitals and other cities, but also to make misleading maps of their own territory, meant to disrupt the movements of anyone who acquired those maps with nefarious intent.

In the early days, the CIA's maps were produced by hand, drawn in pen on translucent sheets that could be stacked, photographed, and printed. But the agency was one of the first to adopt digital technology.

"In 1966, a large working group, using a borrowed digitizer, compiled and digitized coastlines and international boundaries for the entire world—in a single weekend," the agency said in a release.

What maps got made varied with the geopolitical challenges of the moment, but as the maps below show, the quality never slacked.


CIA

CHINESE RAILROAD CONSTRUCTION IN THE MID-1950S.

CIA

OIL TRANSPORT AND REFINING FACILITIES IN THE MIDDLE EAST IN THE EARLY 1950S.


CIA

A MAP OF FRENCH AND VIET MINH AREAS OF OPERATIONS DURING THE 1950S.


CIA

INTERNATIONAL TRADE FLOWS IN THE 1950S.


CIA

SUSPECTED SITES OF MISSILES IN CUBA, 1962.


CIA

TRANSPORTATION ROUTES IN AND AROUND WEST AND EAST BERLIN IN THE 1960S.


CIA

THE CHINA-INDIA BORDER REGION IN 1963.


CIA

BANTUSTANS IN SOUTH AFRICA IN 1973.


CIA

ETHNIC GROUPS IN AFGHANISTAN IN 1979.


CIA

SOUTHERN LEBANON AND ENVIRONS IN 1977.


CIA

CENTRAL MOSCOW IN 1980.


CIA

POPULATION CHANGES DUE TO REFUGEE MOVEMENT ON THE AFGHANISTAN-PAKISTAN BORDER, 1982.


CIA

YUGOSLAVIA IN 1981.


CIA

VATICAN CITY, 1984.

Does an anomaly in the Earth’s magnetic field portend a coming pole reversal?

February 5, 2017
What’s north would become south

The Conversation

John Tarduno and Vincent Hare

The Earth is blanketed by a magnetic field. It’s what makes compasses point north, and protects our atmosphere from continual bombardment from space by charged particles such as protons. Without a magnetic field, our atmosphere would slowly be stripped away by harmful radiation, and life would almost certainly not exist as it does today.

You might imagine the magnetic field is a timeless, constant aspect of life on Earth, and to some extent you would be right. But Earth’s magnetic field actually does change. Every so often – on the order of several hundred thousand years or so – the magnetic field has flipped. North has pointed south, and vice versa. And when the field flips it also tends to become very weak.

On the left, the Earth’s magnetic field we’re used to. On the right, a model of what the magnetic field might be like during a reversal. NASA/Gary Glazmaier, CC BY

What currently has geophysicists like us abuzz is the realization that the strength of Earth’s magnetic field has been decreasing for the last 160 years at an alarming rate. This collapse is centered in a huge expanse of the Southern Hemisphere, extending from Zimbabwe to Chile, known as the South Atlantic Anomaly. The magnetic field strength is so weak there that it’s a hazard for satellites that orbit above the region – the field no longer protects them from radiation which interferes with satellite electronics.

And the field is continuing to grow weaker, potentially portending even more dramatic events, including a global reversal of the magnetic poles. Such a major change would affect our navigation systems, as well as the transmission of electricity. The spectacle of the northern lights might appear at different latitudes. And because more radiation would reach Earth’s surface under very low field strengths during a global reversal, it also might affect rates of cancer.

We still don’t fully understand what the extent of these effects would be, adding urgency to our investigation. We’re turning to some perhaps unexpected data sources, including 700-year-old African archaeological records, to puzzle it out.

Genesis of the geomagnetic field

Cutaway image of the Earth’s interior. Kelvinsong, CC BY-SA

Earth’s magnetic field is created by convecting iron in our planet’s liquid outer core. From the wealth of observatory and satellite data that document the magnetic field of recent times, we can model what the field would look like if we had a compass immediately above the Earth’s swirling liquid iron core.

These analyses reveal an astounding feature: There’s a patch of reversed polarity beneath southern Africa at the core-mantle boundary where the liquid iron outer core meets the slightly stiffer part of the Earth’s interior. In this area, the polarity of the field is opposite to the average global magnetic field. If we were able to use a compass deep under southern Africa, we would see that in this unusual patch north actually points south.

This patch is the main culprit creating the South Atlantic Anomaly. In numerical simulations, unusual patches similar to the one beneath southern Africa appear immediately prior to geomagnetic reversals.

The poles have reversed frequently over the history of the planet, but the last reversal is in the distant past, some 780,000 years ago. The rapid decay of the recent magnetic field, and its pattern of decay, naturally raises the question of what was happening prior to the last 160 years.
Archaeomagnetism takes us further back in time

In archaeomagnetic studies, geophysicists team with archaeologists to learn about the past magnetic field. For example, clay used to make pottery contains small amounts of magnetic minerals, such as magnetite. When the clay is heated to make a pot, its magnetic minerals lose any magnetism they may have held. Upon cooling, the magnetic minerals record the direction and intensity of the magnetic field at that time. If one can determine the age of the pot, or the archaeological site from which it came (using radiocarbon dating, for instance), then an archaeomagnetic history can be recovered.

Using this kind of data, we have a partial history of archaeomagnetism for the Northern Hemisphere. In contrast, the Southern Hemisphere archaeomagnetic record is scant. In particular, there have been virtually no data from southern Africa – and that’s the region, along with South America, that might provide the most insight into the history of the reversed core patch creating today’s South Atlantic Anomaly.

But the ancestors of today’s southern Africans, Bantu-speaking metallurgists and farmers who began to migrate into the region between 2,000 and 1,500 years ago, unintentionally left us some clues. These Iron Age people lived in huts built of clay, and stored their grain in hardened clay bins. As the first agriculturists of the Iron Age of southern Africa, they relied heavily on rainfall.

Grain bins of the style used centuries ago. John Tarduno, CC BY-ND

The communities often responded to times of drought with rituals of cleansing that involved burning mud granaries. This somewhat tragic series of events for these people was ultimately a boon many hundreds of years later for archaeomagnetism. Just as in the case of the firing and cooling of a pot, the clay in these structures recorded Earth’s magnetic field as they cooled. Because the floors of these ancient huts and grain bins can sometimes be found intact, we can sample them to obtain a record of both the direction and strength of their contemporary magnetic field. Each floor is a small magnetic observatory, with its compass frozen in time immediately after burning.

With our colleagues, we’ve focused our sampling on Iron Age village sites that dot the Limpopo River Valley, bordered today by Zimbabwe to the north, Botswana to the west and South Africa to the south.

What’s happening deep within the Earth, beneath the Limpopo River Valley? John Tarduno

Magnetic field in flux

Sampling at Limpopo River Valley locations has yielded the first archaeomagnetic history for southern Africa between A.D. 1000 and 1600. What we found reveals a period in the past, near A.D. 1300, when the field in that area was decreasing as rapidly as it is today. Then the intensity increased, albeit at a much slower rate.

The occurrence of two intervals of rapid field decay – one 700 years ago and one today – suggests a recurrent phenomenon. Could the reversed flux patch presently under South Africa have happened regularly, further back in time than our records have shown? If so, why would it occur again in this location?

Over the last decade, researchers have accumulated images from the analyses of earthquakes’ seismic waves. As seismic shear waves move through the Earth’s layers, the speed with which they travel is an indication of the density of the layer. Now we know that a large area of slow seismic shear waves characterizes the core mantle boundary beneath southern Africa.

Location of the South Atlantic Anomaly. Michael Osadicw/John Tarduno, CC BY-ND

This particular region underneath southern Africa has the somewhat wordy title of the African Large Low Shear Velocity Province. While many wince at the descriptive but jargon-rich name, it is a profound feature that must be tens of millions of years old. While thousands of kilometers across, its boundaries are sharp. Interestingly, the reversed core flux patch is nearly coincident with its eastern edge.

The fact that the present-day reversed core patch and the edge of the African Large Low Shear Velocity Province are physically so close got us thinking. We’ve come up with a model linking the two phenomena. We suggest that the unusual African mantle changes the flow of iron in the core underneath, which in turn changes the way the magnetic field behaves at the edge of the seismic province, and leads to the reversed flux patches.

We speculate that these reversed core patches grow rapidly and then wane more slowly. Occasionally one patch may grow large enough to dominate the magnetic field of the Southern Hemisphere – and the poles reverse.

The conventional idea of reversals is that they can start anywhere in the core. Our conceptual model suggests there may be special places at the core-mantle boundary that promote reversals. We do not yet know if the current field is going to reverse in the next few thousand years, or simply continue to weaken over the next couple of centuries.

But the clues provided by the ancestors of modern-day southern Africans will undoubtedly help us to further develop our proposed mechanism for reversals. If correct, pole reversals may be “Out of Africa.”

Well, This Might Be The Most Artistic Climate Change Ad You've Ever Seen

By Louise Jack
Feb 7, 2017

Charles Dance leads British stars of stage and screen in a poetic "Love Song" ode to Earth for climate charities.


Charles Dance


WHAT: "A Love Song", a poetic tribute to Earth from a group of U.K. charities and organizations committed to tackling climate change.


WHO: The Climate Coalition, Ridley Scott Associates

WHY WE CARE: When Charles Dance’s says, darkly, "I’ve heard talk of a quiet violence waiting at the water’s edge," one sits up and pays attention. But, although this film begins with loss and foreboding, it unfolds into a lyrical message of hope. Dance is joined by fellow actors Miranda Richardson, Jason Isaacs and David Gyasi. Each recites a section of a script written by British poet Anthony Anaxagorou after which the background soundtrack swells into a majestic choral version of Elbow’s Magnificent (She Says).


David Gyasi


The Climate Coalition is an alliance of more than 100 U.K. charities and other organizations, including WWF U.K., 350.org, Friends of the Earth, and Greenpeace U.K., all with an interest in combatting climate change. In a statement, the film’s director, Stuart Rideout, alludes to the current disturbing political attitudes to climate change, "We are entering difficult times in terms of how the world views and reacts to climate change. Engagement with the subject is more important now than ever, " he says. How right he is.

As California goes from drought to deluge, a dangerous old foe returns: Mudslides

LA Times

Rosanna Xia , Raoul Rañoa and Raoul Rañoa/Jan 22, 2017

Through five years of severe drought, El Capitan Canyon above the Pacific Ocean near Goleta endured bone-dry conditions that at times seemed like they would never end.

Then, on Friday, the skies opened up. Nearly 2 inches of rain dropped in a single hour in the Santa Ynez Mountains.

So a creek that had once disappeared came roaring alive, full of mud, brush and broken trees pouring from the burned slopes of the Sherpa fire in the summer.

Five cabins were lifted off their foundations and swept down the creek. The muddy torrent claimed 22 vehicles. One of the cabin’s remains were found south of the 101 Freeway. Nearly two dozen people had to be rescued, including one trapped in a car, said Santa Barbara County fire Capt. Dave Zaniboni. The remains of five smashed vehicles floated all the way down to the beach.

What happened in a matter of minutes at the campground is emblematic of the drought-to-deluge cycle that has always been at the heart of California’s climate. All it can take is an intense amount of rain in a short amount of time to create damaging flows of mud and debris that can kill people and destroy buildings.

The flows are part of nature. But the situation has become more dangerous as humans came to inhabit these paths of destruction.

“There’s a competition between the growth of the mountains and the erosion from the rainstorms,” U.S. Geological Survey hydrologist Jason Kean said. “They’re in this constant battle.”


Flood waters and a debris flow sweep away cabins and vehicles at El Capitan Canyon Resort & Campground in Santa Barbara County Friday. (Mike Eliason / Santa Barbara County Fire)


California’s dramatic shift in the last few months — from extreme dryness to some of the strongest storms in a decade — has brought mudslides that have closed roads, damaged vehicles and homes and left residents on edge. On Friday night, Highway 17 — the key route between Silicon Valley and Santa Cruz — was closed for hours after sliding mud and a fallen tree blocked all southbound lanes, causing a commuter nightmare.


Floodwaters and a debris flow carry away a vehicle at El Capitan Canyon. (Mike Eliason / Santa Barbara County Fire Dept.)

One Sierra highway alone has endured nearly 20 major slides. And a rare warm winter storm two weeks ago sent rains that deposited 10,000 cubic yards of decomposed granite that shut down all westbound lanes of Interstate 80 west of Lake Tahoe for more than 12 hours.

“It’s truly a battle,” Caltrans spokeswoman Liza Whitmore said.

The situation is expected to get worse in Southern California on Sunday, when a storm — which could be the most powerful to strike the region since 2010 — moves in. Officials have warned of mudslides and mudflows.

Why do landslides happen during a storm?

In a burned area, a wildfire can make the soils repellent to water, creating a floodlike flow on the ground that picks up rock and debris, Kean said.

In an area that has not burned, soil can become saturated. Pressure builds up underground, and soil starts moving and begins picking up mud and debris as it starts flowing downhill.

Water rushing down with only mud is called a mud flow. If the flow picks up rocks, branches and sometimes massive boulders, that’s called a debris flow.


This debris flow on Jan. 8, 2017 was caused by a warm winter storm that dumped rain on the Sierra, sending a flow of water and decomposed granite to wash over Interstate 80 at Donner Summit. (California Highway Patrol)


A shallow landslide over Highway 49 in the Sierra Nevada, north of Camptonville, Calif. on Jan. 20, 2017. This route has endured nearly 20 major slides between Nevada City and Sierraville. (Caltrans District 3)


Mud and debris flows are types of shallow landslides, generally defined as less than 15 feet deep.

Another type of shallow landslide involves a saturated hillside that collapses but does not move very far, such as one that buries a roadway with dirt and rocks from a neighboring slope. They can happen up to an hour after a burst of intense rain. “There were widespread shallow landslides as recently as 2005” in Southern California, Kean said.

What’s the easiest type of landslide to predict?

Landslides that strike in recently burned areas are the easiest to predict, as wildfires have burned away roots of trees and vegetation that had kept soils in place.

Sometimes, authorities have accurately predicted when debris flows will occur, based on forecast rainfall rates, and have called for evacuations of homes before the rivers of mud and debris begin flowing.


A debris flow in Duarte sent mud and rocks down Mel Canyon Road Friday. (Irfan Khan / Los Angeles Times)


Can debris flow still catch people off guard?

Yes. In 2010, the winter after the worst fire in L.A. County history, a debris flow — which one resident described like a “Niagara Falls” — flowed down La Cañada Flintridge’s northernmost neighborhood when a 10-ton boulder clogged a critical basin, plugging up the drain like a giant stopper. More than 40 homes were damaged.

It came as a surprise because the storm was supposed to be fast moving, but unexpectedly stalled and dumped rain at an alarming rate. The forecast that authorities had relied on in the days leading up to the three-day storm had called for a light to moderate rains. No evacuations had been ordered.


A debris flow hit La Canada Flintridge in 2010. Mud and debris came rushing through an entire house on Manistee Drive. (Allen J. Schaben / Los Angeles Times)


How much rainfall is needed to trigger mud or debris flow?

In Southern California’s unburned areas, 10 inches of rainfall during the winter is needed to nearly saturate the ground. After that point, a burst of rain of just one-quarter of an inch an hour can trigger widespread shallow landslides, including debris flow, Kean said.

Since July 1, downtown Los Angeles has received 11.33 inches of rain as of Friday, which is 178% of average at this point of the winter. Santa Barbara has received 12.03 inches, which is 149% of average.

But for burned areas, mud and debris flows can strike with only intense rainfall, even if the ground is not saturated.

What’s the least predictable type of landslide?

The kind that can strike on a dry day.

In areas where the bedrock is very deep, rainwater can seep deep underground during multiple rainstorms. During a series of repeated heavy storms, water can eventually start to accumulate and build up pressure, Kean said.

The pressure can destabilize an entire chunk of land, causing it to collapse downhill. The landslide can happen slowly, and show warning signs like cracking or subtle movements, allowing people time to escape. But they can also strike rapidly with no warning, even on a rainless day months after the end of winter.

This is called a deep-seated landslide, involving landslides greater than 15 feet deep. Often, deep-seated landslides strike in areas with a history of such events. The USGS has warned that such landslides can become active many months after a very wet winter.


A deep-seated landslide struck Bluebird Canyon of Laguna Beach in 2005. (Mark Boster / Los Angeles Times)


What’s an example of a deep-seated landslide?

An example of where a deep-seated landslide has occurred is Bluebird Canyon of Laguna Beach.

One occurred on a foggy morning in June 2005 after heavy rains fell between the previous December through February. No rainfall occurred during or just before the landslide. Seventeen homes were destroyed and 11 seriously damaged.

There has been a history of devastating landslides in Bluebird Canyon. The neighborhood suffered a slide in October 1978 that destroyed more than 20 homes. The California Division of Mines and Geology said the heavy rains between December 1977 through April 1978 are believed to have played a role, along with a history of landslides and erosion at the site, and weakness in the rock.

What about the coastal hamlet of La Conchita in Ventura County? Did landslides there come as surprises?

The first landslide, in March 1995, came as no surprise, Ventura County geologist Jim O’Tousa said. The summer before, officials had observed ground cracks and other signs of a pending landslide. A sheriff’s official was assigned to patrol the area, and town meetings were held to prepare the community for what was coming.

Then about 24 inches of rain hit the region in January — way above the average of about 4 inches for that month. The slide hit March 2. The slopes started sliding at a pace so slow that residents could outrun it. The patrol officer was still knocking on doors as the ground was moving and got everyone down the hill in time, O’Tousa recalled.

“The groundwater finally built up to a high enough level to destabilize the slope,” O’Tousa said.


A deep-seated landslide buried 10 people, killing them, in 2005 in La Conchita. (Stephen Osman / Los Angeles Times)


The second landslide in 2005 occurred at the end of an intense 15-day rainy period that saw heavy precipitation throughout Southern California. This slide came with no warning, and buried 10 people, killing them.

The 2005 landslide was actually a “remobilization of part of the 1995 slide,” O’Tousa said. The 1995 landslide had fractured and was sitting in the bottom of the canyon, he explained. Then in 2005, when enough water saturated the bottom of the canyon, the material came flushing out of the canyon — a speed of 20 mph — and flowed into the neighborhood where the fatalities occurred.


In this photo taken Jan. 27, 2016, crumbling cliffs threaten homes, apartment buildings and businesses in Pacifica, Calif. (Monica Davey / EPA)


What about cliffs that fall into the sea?

Last winter, California saw cliffs erode into the sea in Pacifica, about a 15-mile drive south of San Francisco. There, apartment units have been ordered vacated because of the crumbling coastline.

Pacifica has some of the weakest soils along the California coast composed of cliffs, USGS research civil engineer Brian Collins said.

The cliffs are being attacked from both the bottom and on top from water. At its base, the ocean is eroding the cliffs. When heavy rains come from above, water seeps into the soils, and eventually exits when it reaches less permeable layers.

The nature of this seepage weakens the bonds in the soil that keep the soil particles bonded together, “so it collapses,” Collins said.

The coast in this region has been eroding for thousands of years. As sea levels have risen, the ocean has eroded the cliffs. And the San Andreas fault has been lifting the cliffs up, only for them to be taken down by the seas and the rain.

ron.lin@latimes.com | @ronlin ■