Friday, September 22, 2017

Mexico City Was Built on an Ancient Lake Bed. That Makes Earthquakes Much Worse.

SIERRA DE
GUADALUPE
Simulated
epicenter
MEXICO
CITY
Area of ancient
lake bed
Shock waves from
a simulated earthquake
The New York Times | Source: Víctor Cruz-Atienza, National University of Mexico
The earthquake that on Tuesday killed at least 135 people in Mexico City and toppled dozens of buildings there was all the more destructive because of the city’s unusual position atop an ancient lake bed.
The animation above, based on a model by Víctor Cruz-Atienza, a professor of geophysics at the National University of Mexico, shows how the shock waves of a hypothetical earthquake near Mexico City would spread. Darker red areas indicate the strongest ground movement.
The shaking in this simulation is strongest in the low parts of the Valley of Mexico, which cradles the city, and it weakens when it meets the surrounding hills. That’s no coincidence. The darker red areas showing the strongest shock waves trace the shape of an ancient lake.
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The Spanish built modern Mexico City over the ruins of the Aztec capital of Tenochtitlan, which they conquered in 1521. The Aztec city was on an island in Lake Texcoco, but the Spanish drained the surrounding lake over centuries and expanded Mexico City onto the new land.
Today, much of the city stands on layers of sand and clay — up to 100 yards deep — that used to be under the lake. These soft, water-laden sediments make the city uniquely vulnerable to earthquakes and other problems.
2 MI.
The city stands on soft
ancient lake sediments.
The lake bed
contains some hills...
...and is surrounded
by mountains.
1 MILE
ABOVE SEA
LEVEL
HARDER ROCK
The New York Times
During an earthquake, the looser sediments near the surface cause shockwaves to slow down from about one and a half miles per second to about 150 feet per second as they enter the valley. The slower waves grow in amplitude, similar to a tsunami approaching a coastline, and cause more violent shaking.
Worse still, the denser, deeper material below the looser sediments causes waves to linger in the valley, making the amplified shaking last longer.
The map below, based on seismological readings taken at the National University of Mexico, shows how violently the ground shook in Mexico City during Tuesday’s earthquake. Like the simulation map, the redder the area, the more violently the ground shook.
MEXICO
CITY
Lake bed
Strength of shaking in Mexico City
The New York Times | Source: The Institute of Engineering at the National University of Mexico
These actual readings confirm what the simulation shows: Tuesday’s earthquake grew worse in the city as its waves moved through the ancient lake bed below.
Mexico City is already a hot spot for earthquakes because vast chunks of the earth’s crust, called tectonic plates, are slowly smashing into one another nearby. Mexico rests on the North American Plate, and the Cocos Plate slides underneath it along the country’s southwestern coast.
MEXICO
200 MILES
Mexico City
TUESDAY’S EPICENTER
COCOS PLATE
The collision as one plate plunges below the other, a movement called subduction, releases huge amounts of energy, making earthquakes a common occurrence in Mexico. Unlike Tuesday’s, many of these earthquakes are small.
The unique geology of Mexico City’s basin can amplify earthquake waves to be a hundred times stronger than they would be otherwise, a phenomenon that Dr. Cruz-Atienza said is not matched anywhere else in the world.
Partly because of this amplification, earthquakes that happen relatively far away from Mexico City can still cause significant damage. A devastating earthquake in 1985 that killed as many as 10,000 people originated over 200 miles away, near the Pacific coast of Mexico.
The epicenter of Tuesday's quake was closer, around 50 miles away, but the map below shows that it shook Mexico City more violently than other areas that were a similar distance from the epicenter.
Mexico City
Puebla
Atlixco
EPICENTER
20 MILES
The New York Times | Source: United States Geological Survey
The 1985 earthquake prompted improvements to building codes that are thought to have lessened the damage on Tuesday. But earthquakes will always pose a unique threat to Mexico City, because of the geologic implications of the ancient lake bed that lies beneath it.

Tuesday, September 12, 2017

Protest in Catalonia Adds to Pressure Before Independence Vote

Photo
Hundreds of thousands of people celebrated the Catalan National Day on Monday in Barcelona. Credit David Ramos/Getty Images
BARCELONA, Spain — Hundreds of thousands of Catalans took over the center of Barcelona on Monday to mark their national day and raise the pressure on the Spanish government in Madrid before an independence referendum planned for Oct. 1.
The referendum has been declared illegal by Prime Minister Mariano Rajoy and suspended by the Spanish judiciary as a violation of Spain’s constitution. But separatist leaders in the Catalan regional government have vowed to go ahead with it, even if they risk prosecution for civil disobedience.
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Photo
Protesters carrying “esteladas” or Catalan flags and other nationalist symbols in support of an Oct. 1 referendum on independence. Credit Santi Palacios/Associated Press
Since 2012, the Diada, or Catalan national day, has been turned into the annual show of force of independence-minded Catalans.
On Monday, the protesters filled two streets of Barcelona to form a “plus” sign, representing citizens joining forces. Some demonstrators said the cross symbolized the mark they will put on their ballots in favor of independence, assuming the referendum goes ahead.
The national day marks a historic defeat for Catalans, the 1714 capture of Barcelona by the troops of Philip V of Spain. “Philip V repressed Catalonia, and three centuries later here we are, getting denied the right to vote in the Spain of Philip VI,” said Oriol Cabré, a retired industrial engineer, referring to the current king.
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Photo
Men wearing of Catalan military costumes from the 18th century performed during the rally. Credit Santi Palacios/Associated Press
Many demonstrators insisted that they would also step up their protests if the result of the vote did not then become binding — as their separatist leaders have promised it would be.
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“Civil disobedience is sadly sometimes the only way,” said Manel Angurem, an international trade consultant who drove for about an hour with his wife and three children to Barcelona to attend the demonstration. “If it weren’t for civil disobedience in the United States, black people wouldn’t have managed to get a seat on the same bus as white people.”
Still, as in previous years, Monday’s protest was a festive and peaceful occasion, with some participants even forming the traditional Catalan castells, or human towers.
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Photo
Performers built a human tower during the demonstration. Credit Emilio Morenatti/Associated Press
Catalans feel strongly about their distinct language, history and culture. But such feelings have become entwined in recent years with other issues, including how much tax revenue Catalonia should redistribute to poorer parts of Spain.
In addition to history, many of the participants cited pocketbook issues in wanting independence, after a financial crisis that helped fuel separatism in Catalonia.
“If we look after our own wealth rather than hand it over to Madrid, I’m sure independence will also bring us better economic conditions,” said Laura Solsona, who has a beauty salon in the town of Sabadell and had painted “Yes” on her forehead and a Catalan flag on her cheek.
Carles Puigdemont, the leader of Catalonia, assured the region’s voters that the independence referendum would take place, despite efforts by the Madrid government and Spanish courts to block it.
Catalan citizens “will vote, as they have always done in complete normality,” Mr. Puigdemont said. A referendum, he argued, would not escalate the secessionist conflict because “the ballot boxes don’t divide, they unite.”
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Photo
The leader of Catalonia, Carles Puigdemont, attended a ceremony to mark the occasion. Credit Toni Albir/European Pressphoto Agency
The demonstrators held a minute’s silence in honor of the victims of the terrorist attacks last month in Catalonia that killed 16 people, most of them mowed down by a van driver on Barcelona’s most famous promenade. Few in the crowds on Monday seemed concerned about security.
“We’ve always shown respect, and we now hope that we can convince others to respect our right to vote and become another normal European state,” said Jesús Ribera, a trade union official, who had a sticker on his sleeve showing Catalonia as a future member state of the European Union.
“I can assure you that all the people here today will be standing in front of the polling stations on Oct. 1, even if they are kept closed and Madrid also manages to seize the ballot papers and boxes.”
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Photo
In addition to hundreds of thousands of protesters, many other independence supporters watched the march. Credit Susana Vera/Reuters
As the political clock ticks toward the Oct. 1 deadline for the referendum, the tension between Madrid and Barcelona is rising. Prime Minister Rajoy is even weighing whether to take emergency measures to stop the vote, a step many fear would deepen the standoff.
Even the crowd estimates were disputed on Monday. Local police put the number at about one million, while representatives from the central government in Barcelona estimated it at between 300,000 and 350,000.

Saturday, September 9, 2017

Hurricane Irma Live Updates: ‘The Storm Is Here,’ Florida Governor Says

Continue reading the main story Video

Hurricane Irma Churns Toward Florida

The Atlantic’s strongest storm has left destruction across the Caribbean. Witnesses warn others to brace themselves as Irma moves toward Florida.
By CAMILLA SCHICK, ROBIN LINDSAY and CHRIS CIRILLO on Publish Date September 6, 2017. Photo by Martin Bureau/Agence France-Presse — Getty Images. Watch in Times Video »
Hurricane Irma churned toward Florida on Saturday, leaving a trail of death and destruction across the Caribbean and prompting one of the largest emergency evacuations in American history.
The storm is driving northwest as it rips across northern Cuba, and will eventually continue toward the United States. It is expected to grip hold of land again by Sunday morning in Florida, where it will most likely move along or near the southwest coast, according to the National Hurricane Center.
Storm surges will threaten Florida’s west coast on Sunday, where more than 3 million people live, and entire neighborhoods stretching northward from Naples to Tampa Bay could be submerged.
Irma made landfall in Cuba Friday evening as a Category 5 hurricane, lashing the island’s northern coast with a direct hit. It became the first Category 5 hurricane to make landfall in Cuba since 1924.
The hurricane was downgraded to Category 3 Saturday morning, with winds of 125 miles per hour, and remained Category 3 around 2 p.m., but was expected to strengthen again over Florida. About 6.3 million people in the state have been ordered to leave their homes.
“The storm is here,” Gov. Rick Scott said Saturday morning, noting that the storm surge could reach 15 feet in some places.
“Fifteen feet is devastating and will cover your house,” he said. “Do not think the storm is over when the wind slows down. The storm surge will rush in and it could kill you.”
Here’s the latest:
• At least 25 people were confirmed dead by Saturday morning in areas affected by the storm.
• Irma’s core is expected to reach the Florida Keys by Sunday morning, with the eye on track to tear between the cities of Key West and Marathon. “THIS IS AS REAL AS IT GETS,” the National Weather Service said. “NOWHERE IN THE FLORIDA KEYS WILL BE SAFE.” The National Hurricane Center warned of “life-threatening surge and wind.” Check out our maps tracking the storm.
• In addition to an evacuation order in Miami, one of the country’s largest evacuations, 540,000 people were told to leave the Georgia coast. Alabama, North Carolina and South Carolina have declared states of emergency.
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Photo
The Palmetto Expressway in Miami on Saturday as Hurricane Irma approached. Credit Scott McIntyre for The New York Times
• At 1 p.m., the National Hurricane Center said a weather station in Ciegode Avila, Cuba, reported a wind gust to 159 m.p.h.
• Hurricane Jose, upgraded to a Category 4, was barreling toward the Leeward Islands. On St. Martin, already devastated by Irma, Dutch Marines dropped fliers from a helicopter warning inhabitants to head to shelters.
• Hurricane Katia, which made landfall on Mexico’s eastern coast, was downgraded to a tropical depression, with winds of 35 m.p.h. Two people died in a mudslide in the state of Veracruz after the storm hit, The Associated Press reported.
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SEVERITY Category 5 4 3 2 1 Tropical storm

Governor to Floridians: Evacuate now

During a news conference Saturday morning, Gov. Rick Scott urged Floridians to heed evacuation orders and seek shelter immediately.
“Evacuate,” he said. “Not tonight, not in an hour. You need to go right now.”
He reassured those who were still delaying that they would not have to leave the state. More than 260 shelters were already operating across every county, with 70 more scheduled to open throughout the day.
Evacuation routes across the state were moving consistently, the governor said, adding that he had dispatched additional state troopers to maintain the flow of traffic.
“Just remember this,” he said, “Once the storm starts, law enforcement cannot save you.”
Volunteers were needed at shelters that were serving people with special needs. “We need more nurses,” the governor said, asking those who were willing to work to email BPRCHDpreparedness@flhealth.gov. “All available nurses, if you’ll please respond.”
Rob Gould, the public information officer for the Florida Power & Light Company, said the company expected 3.4 million customers to be affected by the storm. Parts of the electrical system will need to be entirely rebuilt, Mr. Gould said, with the company expecting the brunt of the damage in the western part of the state.
“Likely on the east coast, we will see a restoration, but on the west coast, a complete rebuild,” he said. “We anticipate this restoration effort will be measured in weeks, not days.”
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Photo
Many homes were destroyed on Virgin Gorda, in the British Virgin Islands. Credit Caribbean Buzz Helicopters/Caribbean Buzz Helicopters, via Associated Press

Florida Keys face being cut off from mainland

In the Florida Keys, where the hurricane is expected to make landfall on Sunday morning between Marathon and Key West, emergency officials girded for a direct hit and residents who did not evacuate began to take cover as the winds kicked up sharply Saturday afternoon.
The Keys, a thin chain of islands that sit below sea level, are especially vulnerable to Hurricane Irma’s anticipated powerful tidal surges.
The ocean is expected to rise and hurtle into buildings and houses near the coast. Pine Island, north of Key West, was already seeing rising seas at noon.
Some canals were spilling their bounds and emergency responders were evacuating to the Upper Keys.
“We’re very concerned about the potential loss of life,” said Cammy Clark, a county spokeswoman. “Storm surges could kill a lot of people because there’s nowhere to go.”
But the worst could come after the hurricane moves on. Keys residents could find themselves isolated from the mainland if any one of their 42 bridges gets damaged.
Residents and emergency officials would be cut off from food, gas and other supplies because there would be no easy way of reaching them by road.
“Just think about the Keys for a second,” Governor Scott warned residents at a recent news conference. “If we lose one bridge, everything south of the bridge, everybody’s going to be stranded. It’s going to take us a while to get back in there to try to provide services.”
With so many dire warnings, some residents left Saturday morning. But others dug in, choosing not to evacuate. Emergency officials grew so concerned about the holdouts they opened four refuges of last resort.

A dangerous storm surge

The winds of Hurricane Irma are fierce. But the surge from the storm could also cause tremendous damage to coastal cities.
“It flows in very fast,” Governor Scott said of the waters expected to rush into parts of the state. “It’s going to go faster, possibly, than you are.”
Continue reading the main story
Photo
Palm trees in Caibarién, Cuba, on Friday, before Hurricane Irma arrived. Credit Desmond Boylan/Associated Press
The National Hurricane Center provides a map of the potential storm surge from Irma, and the 5 a.m. Saturday forecast suggested a brutal surge near Naples topping nine feet.
More detailed projections can be found at the website adcirc.org, which is devoted to a highly respected suite of computer programs that model surge. Rick Luettich, one of the principal developers of Adcirc and director of the University of North Carolina, Chapel Hill’s Institute of Marine Sciences, said that the current map of Florida under the models “looks a bit ugly,” which he acknowledged was an understatement.
“For years, we have thought about areas of the country that are particularly vulnerable to hurricanes, and particularly, storm surge,” Dr. Luettich said. New York City, New Orleans, Houston, and Miami are always high on such lists. “It’s almost as if we’ve been going down the list and checking them off,” he said.
The projections on the site, which are based on the forecasts from the National Hurricane Center and updated with each new forecast, allow users to look at any given report and see what would happen if the storm track shifts 50 percent to the west or to the east. (To try this, go to the map, pull down the advisory/track tab and hover your cursor over any report.)
With this storm, Dr. Luettich noted, those shifts can mean major differences in destructive storm surge for the Atlantic or Gulf coasts of Florida and farther up the Atlantic coast.

‘Run from the water, hide from the wind’

A hurricane watch took effect for the entire Georgia coast on Saturday, and a mandatory evacuation order covered most of the coast.
Officials warned of the potential for high winds and storm surge even as Irma’s forecasted path seemed likely to spare the region from the worst.
“Run from the water, hide from the wind,” said Dennis Jones, the director of emergency management in Chatham County, which contains Savannah. “Our focus is to get you out of the threat.”
Hundreds of people lined up outside of the convention center in Savannah, waiting for school and coach buses to evacuate them out of the city.
Doretha Harden, 53, stood with six of her neighbors from a housing complex for disabled residents. Ms. Harden has a brain disorder and was worried, she said, that the tension of the evacuation could give her a seizure.
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Boarding up windows in Miami on Friday in preparation for Hurricane Irma. Credit Scott McIntyre for The New York Times
“It’s triggered by stress,” she said.
Lorenzo Green, 66, said he worried more about the evacuation than the storm itself.
“I’m supposed to be going to Augusta,” Mr. Green said. “The only thing that’s scary is going to a place I’ve never been.”

Cuba gets a direct hit

Irma slammed into Cuba on Friday night as a Category 5 hurricane, causing widespread destruction. Meteorologists were expecting the storm to tack north earlier, and were not predicting a direct hit.
The eye of the storm passed directly through the archipelago of keys on the northern coast in the central part of the island.
Irma, downgraded to Category 3, continued to plow through Cuba on Saturday afternoon.
The damage to its central provinces was substantial: Power lines were brought down in Camaguey, houses were destroyed in Ciego de Avila and fishing towns have been submerged in Villa Clara.
By Saturday afternoon, the storm started to lash Havana. By 1 p.m. waves were crashing over the capital’s iconic breakwater and esplanade, the Malecón. Apart from the police, the only people out were a few thrill-seeking tourists.
Havana is set to avoid the brunt of the storm, but meteorologists warned that flooding could penetrate over 500 meters into the city.

An ‘apocalyptic doomsday scene’ on the British Virgin Islands

With communications limited on the British Virgin Islands, the full scope of the damage from Hurricane Irma was still revealing itself. On Saturday, at least five deaths were reported by the governor, Gus Jaspert. With communication on the island all but severed, officials were still working to assess the full scale of devastation.
Residents of Tortola, the largest island, said buildings were leveled and roads were washed away. People have limited food and water.
Mr. Jaspert said the toll on the islands was widespread and he urged citizens to prepare for incoming Hurricane Jose.
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Photo
Salvaging items from a flooded home in Fort-Liberté, Haiti, on Friday. Credit Dieu Nalio Chery/Associated Press
The British government said it sent 20 tons of aid to the affected areas, including shelter kits and solar lanterns aboard a naval ship.
Catherine Clayton, whose family owns a hotel on Tortola in Josiah’s Bay, said 25 people — including neighbors whose homes were decimated — were sheltered in the two remaining inhabitable rooms at the once eight-room Tamarind Hotel.
“It is like an apocalyptic doomsday scene here,” she said. “No trees, leaves or greenery.”
Other parts of the island had similar damage. From her apartment on Skelton Hill, which overlooks Road Town, the capital, Christine Perakis said most of the homes had their roofs torn off.
“We have been in shock for a couple of days,” she said. “It’s the most intense thing I’ve ever seen.”

Severe flooding in the Bahamas

Residents of the western Bahamas braced for Irma on Saturday even as the hurricane ripped apart sea walls, destroyed wooden homes and eroded roads on the nearby southern and central islands.
Severe flooding was reported on Acklins, where the settlement of Salina Point was cut off from the rest of the island, according to early reports from that area.
“There’s been significant damage to houses on Ragged Island, and in certain parts of Acklins there’s been a lot of road erosion,” said Dion Foulkes, the Bahamas’ minister of labor and consumer affairs, and a liaison with the National Emergency Management Agency in Nassau.
He said stone structures had fared well in the storm, and so far there have been no reports of deaths or injuries.
As soon as conditions permit, the Jamaican Defense Force has agreed to survey the affected Bahamian islands, Hubert Minnis, the Bahamian prime minister, said.
Bimini, Grand Bahama and Andros are expected to be the last group of Bahamian islands affected by Irma, starting early Sunday through Monday morning.
Around 300 residents of Bimini have been evacuated, and residents of the low-lying West End, Grand Bahama, have been urged to relocate east.

Wednesday, August 23, 2017

Alaska’s Permafrost Is Thawing






RUSSIA
BEAUFORT SEA
PERMAFROST
ALASKA
CANADA
BERING
SEA
GULF OF
ALASKA

Alaska’s permafrost, shown here in 2010, is no longer permanent. It is starting to thaw.

By 2050, much of this frozen ground, a storehouse of ancient carbon, could be gone.

This is what may be lost.


YUKON DELTA NATIONAL WILDLIFE REFUGE, Alaska — The Arctic is warming about twice as fast as other parts of the planet, and even here in sub-Arctic Alaska the rate of warming is high. Sea ice and wildlife habitat are disappearing; higher sea levels threaten coastal native villages.
But to the scientists from Woods Hole Research Center who have come here to study the effects of climate change, the most urgent is the fate of permafrost, the always-frozen ground that underlies much of the state.
Starting just a few feet below the surface and extending tens or even hundreds of feet down, it contains vast amounts of carbon in organic matter — plants that took carbon dioxide from the atmosphere centuries ago, died and froze before they could decompose. Worldwide, permafrost is thought to contain about twice as much carbon as is currently in the atmosphere.
Once this ancient organic material thaws, microbes convert some of it to carbon dioxide and methane, which can flow into the atmosphere and cause even more warming. Scientists have estimated that the process of permafrost thawing could contribute as much as 1.7 degrees Fahrenheit to global warming over the next several centuries, independent of what society does to reduce emissions from burning fossil fuels and other activities.



Stash Wislocki

In Alaska, nowhere is permafrost more vulnerable than here, 350 miles south of the Arctic Circle, in a vast, largely treeless landscape formed from sediment brought down by two of the state’s biggest rivers, the Yukon and the Kuskokwim. Temperatures three feet down into the frozen ground are less than half a degree below freezing. This area could lose much of its permafrost by midcentury.
That, said Max Holmes, senior scientist and deputy director of the research center, “has all kinds of consequences both locally for this region, for the animals and the people who live here, as well as globally.”
“It’s sobering to think of this magnificent landscape and how fundamentally it can change over a relatively short time period,” he added.



Max Holmes, deputy director and senior scientist of the Woods Hole Research Center. Stash Wislocki

But on this wide, flat tundra, it takes a practiced eye to see how Alaska is thawing from below.
At one of the countless small lakes that pepper the region, chunks of shoreline that include what had been permafrost have calved off toward the water.
Nearby, across a spongy bed of mosses and lichens, a small boggy depression likely formed when the ice in the top layers of the permafrost below it melted to water.



John Schade


John Schade
In July, the Woods Hole scientists, along with 13 undergraduate and graduate students working on projects of their own, set up a temporary field station on a nameless lake 60 miles northwest of Bethel, which with a population of 6,000 is the largest town in the region. They drilled permafrost cores with a power auger, took other sediment and water samples and embedded temperature probes in the frozen ground. Later, back in the lab at Woods Hole, they began the process of analyzing the samples for carbon content and nutrients.
The goal is to better understand how thawing permafrost affects the landscape and, ultimately, how much and what mix of greenhouse gases is released.
“In order to know how much is lost, you have to know how much is there,” said Sue Natali, a Woods Hole scientist and permafrost expert.
Even in colder northern Alaska, where permafrost in some parts of the North Slope extends more than 2,100 feet below the surface, scientists are seeing stark changes. Vladimir E. Ramonovsky, a permafrost researcher at the University of Alaska, Fairbanks, said that temperatures at a depth of 65 feet have risen by 3 degrees Celsius (about 5.5 degrees Fahrenheit) over decades.
Near-surface changes have been even greater. At one northern site, he said, permafrost temperatures at shallow depths have climbed from minus 8 degrees Celsius to minus 3.
“Minus 3 is not that far from zero,” Dr. Romanovsky said. If emissions and warming continue at the same rate, he said, near-surface temperatures will rise above freezing around the middle of the century.



Max Holmes and Sue Natali of the Woods Hole Research Center. Stash Wislocki

There is plenty of debate among scientists about when and how much of Alaska’s permafrost will thaw. And there is no doubt that thawing of the full depth of permafrost would take millenniums.
But Dr. Romanovsky said that his and others’ work shows that permafrost “is not as stable as people thought.”
In addition to greenhouse gas emissions, thawing wreaks havoc on infrastructure, causing slumping of land when ice loses volume as it turns to water.
The main road in Bethel, where average temperatures have risen about 4 degrees Fahrenheit since the mid-20th century, is more of a washboard than a thoroughfare because of shifting ground. Building foundations in Bethel move and crack as well. Some roads, airport runways and parking areas have to be reinforced with liquid-filled pipes that transfer heat out of the permafrost to keep the ground from slumping.
The thawing of permafrost is a gradual process. Ground is fully frozen in winter, and begins to thaw from the top down as air temperatures rise in spring. As average temperatures increase over years, this thawed, or active, layer can increase in depth.
At the field station, the researchers are especially interested in how wildfires affect the permafrost. Because burning removes some of the vegetation that acts as insulation, the theory is that burning should cause permafrost to thaw more.











In the field, Sarah Ludwig, a Woods Hole research assistant (left), and a student, Laura Jardine, extract a core of permafrost. In the lab, Ms. Jardine cuts the core with a saw. Stash Wislocki, except for last photo, by John Schade
Parts of the tundra here burned in the 1970s and in the summer of 2015, so the researchers took cores from both burned and unburned areas. Scientists wrestled with the bulky power auger as its stainless steel tube worked its way into the hard permafrost. Cores — often containing thin layers of solid ice — were labeled, packed in a cooler and sent by helicopter to a freezer in Bethel.
Thawing permafrost underneath or at the edge of a lake can cause it to drain like a leaky bathtub. Thawing elsewhere can bring about small elevation changes that can in turn lead to changes in water flow through the landscape, drying out some parts of the tundra and turning others into bogs.
Beyond the local effects on plant and animal life, the landscape changes can have an important climate change impact, by altering the mix of carbon dioxide and methane that is emitted. Although methane does not persist in the atmosphere for as long as carbon dioxide, it has a far greater heat-trapping ability and can contribute to more rapid warming.
So the researchers devote much of their time to studying the flow of water and the carbon and nutrients it contains.



John Schade

“It’s one of the big questions to tackle – what’s wet and dry now, and what will be wet and dry in the future,” Dr. Natali said. If the decomposing permafrost is wet, there will be less oxygen available to the microbes, so they will produce more methane. If the permafrost is dry, the decomposition will lead to more carbon dioxide.
Estimates vary on how much carbon is currently released from thawing permafrost worldwide, but by one calculation emissions over the rest of the century could average about 1.5 billion tons a year, or about the same as current annual emissions from fossil-fuel burning in the United States.
Already, thawing permafrost and warmer temperatures are being blamed for rising carbon emissions in the Alaskan tundra, both here and farther north. In a study earlier this year, researchers found that bacterial decomposition of thawed permafrost, as well as carbon dioxide produced by living vegetation, continues later into the fall because freezing of the surface is delayed.
The rise in emissions has been so significant, the researchers found, that Alaska may be shifting from a sink, or storehouse, of carbon, to a net source.
Dr. Holmes said that shift was not surprising given the climate trend, and he would expect that sub-Arctic parts of Siberia, Canada and other areas with permafrost may be undergoing similar changes.
“There’s a massive amount of carbon that’s in the ground, that’s built up slowly over thousands and thousands of years,” he said.
“It’s been in a freezer, and that freezer is now turning into a refrigerator.”
Correction August 23, 2017
An earlier version of this article referred incorrectly to an estimate of the amount of carbon released from thawing permafrost worldwide. It is 1.5 billion tons a year averaged over the remainder of the century, not 1.5 billions tons a year currently.
Note: Highlighted areas of maps show over 50% probability of permafrost within one meter of ground surface.
Source: Data from “Distribution of Near-Surface Permafrost in Alaska: Estimates of Present and Future Conditions” by Neal J. Pastick and others in Remote Sensing of Environment, October 2015.