Earth

The Los Angeles wildfires were still burning when scientists started scouting the freshly charred burn scars to search for signs of another danger that’s yet to come — roaring torrents of rock and mud and water that can sweep downhill with deadly momentum.

Triggered by intense bouts of rainfall, these debris flows — as well as flash floods — become more likely to occur after an intense wildfire has scorched an area’s slopes and vegetation. While flash floods can be devastating, debris flows surge with even greater ferocity. At least half of their volume is sediment, and it’s mixed with burned trees, cars and boulders. More

Shifting is in a river’s nature. But when a river breaks free of its channel and carves a new path across the landscape, devastating floods may descend upon communities with little to no warning.

For decades, researchers have struggled to explain exactly how river channels become primed for such sudden diversions, or avulsions. A study published September 18 in Nature may have finally quelled the debate, showing how two factors work together to stage the rerouting of a river. Building on their findings, the researchers also developed a promising algorithm that can predict the new path of a river that has avulsed. More

Meteorologist Thea Sandmael watched the storm close in. It was near enough for her to spot a rotating dome of clouds emerging from its dark underbelly — the quickening of a tornado. By the time the spinning mass was 10 minutes away, Sandmael and her colleagues had shut down their radar instruments and evacuated their post.

“Just keep going,” she advised her colleague behind the wheel, who was rightly focused on maneuvering their SUV down the remote Alabama road. Following behind was another colleague in a truck carrying their cumbersome radar equipment. Evacuating was a good decision, she reflects: “We were sitting on the west side of the road, and the tornado touched down in our exact location.” More

The strongest solar flare in recorded history burst into Earth’s atmosphere in 1859, bathing both hemispheres in brilliantly colorful aurorae as it wreaked worldwide havoc on telegraph systems. The celestial chaos was broadly witnessed, but lingering physical evidence of that storm, dubbed the Carrington event, has proven stubbornly elusive — until now, researchers report in the March 16 Geophysical Research Letters.

Ecologist Joonas Uusitalo of the University of Helsinki and his colleagues have identified the first known traces of the Carrington event: atoms of carbon-14 preserved in tree rings in Finland’s far north. Scientists previously hadn’t detected tree ring evidence of this event, although other trees have recorded more powerful solar flares that occurred before modern recordkeeping began, such as in 774 and 993. More

Climate change may be making it harder to know exactly what time it is.

The rapid melting of the ice sheets atop Greenland and Antarctica, as measured by satellite-based gravitational measurements, is shifting more mass toward Earth’s waistline. And that extra bulge is slowing the planet’s rotation, geophysicist Duncan Agnew reports online March 27 in Nature. That climate change–driven mass shift is throwing a new wrench into international timekeeping standards.

The internationally agreed-upon coordinated universal time, or UTC, is set by atomic clocks, but that time is regularly adjusted to match Earth’s actual spin. Earth’s rotation isn’t always smooth sailing — the speed of the planet’s spin changes depending on a variety of factors, including gravitational drag from the sun and the moon, changes to the rotation speed of Earth’s core, friction between ocean waters and the seafloor, and shifts in the planet’s distribution of mass around its surface. Even earthquakes can affect the spin: The magnitude 9.1 earthquake in Indonesia in 2004, for example, altered the land surface in such a way that it caused Earth to rotate a tiny bit faster, says Agnew, of the Scripps Institution of Oceanography in La Jolla, Calif. More

The world’s precious stash of subterranean freshwater is shrinking — and in nearly a third of aquifers, that loss has been speeding up in the last couple of decades, researchers report in the Jan. 25 Nature.

A one-two punch of unsustainable groundwater withdrawals and changing climate has been causing global water levels to fall on average, leading to water shortages, slumping land surfaces and seawater intrusion into aquifers. The new study suggests that groundwater decline has accelerated in many places since 2000, but also suggests that these losses can be reversible with better water management. More

SAN FRANCISCO — Most of the news regarding the Thwaites Glacier, a Florida-sized slab of ice that is melting and currently contributing about 4 percent of global sea level rise, is bad. But a bit of good news may have emerged.

A seismic survey of the bed beneath an upstream section of Thwaites has revealed rough high-rises of earth under the Antarctic glacier, which are comparable in height to the Manhattan skyline, glaciologist Coen Hofstede reported December 12 at a news conference during the American Geophysical Union fall meeting. These rugged rises may be snagging the glacier’s underbelly, slowing its flow toward the ocean and mitigating global sea level rise.

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Glaciers flow somewhat like rivers, but much slower. Where Thwaites outlets into the ocean, it connects to a floating shelf of ice that braces and partially restrains the glacier. That ice shelf was once pinned upon an underwater mountain, which helped stabilize it (SN: 12/13/21). But now the shelf is so deteriorated that it’s basically unhitched, Erin Pettit, a glaciologist at Oregon State University in Corvallis, said at the news event.

Fortunately, though, the glacier “is not going to suddenly flow off land,” thanks partly to what’s been discovered upstream, said Pettit, who was not involved in the discovery.  

To image Thwaites’ underbelly, researchers used a tractorlike vehicle (background, center) to haul a seismic vibrator truck on a sled, as well as a 1.5-kilometer-long chain of seismometers (foreground), across the glacier’s surface. A caboose-train (left) used for cooking, eating and repairs accompanied the vibrator truck across the ice. Coen Hofstede

More than 70 kilometers inland from Thwaites’ ice shelf, Hofstede and his colleagues conducted a seismic survey to probe the glacier’s underbelly. The team attached a 1.5-kilometer-long daisy-chain of seismometers to a vehicle equipped with a vibrating plate. Then they drove a roughly 200-kilometer-long stretch of the glacier, using the plate to generate seismic waves and the seismometers to record the waves’ reflectance off layers of ice and earth below. “It’s almost like radar,” said Hofstede, of the Alfred Wegener Institute Helmholtz Center for Polar and Marine Research in Bremerhaven, Germany.

A Pisten Bully (center left), a tracked vehicle able to maneuver on the ice, tows seismic equipment (red) across Thwaites Glacier. A second Pisten Bully (right) hauls the
accommodation train with the crew’s sleeping tents.Ole Zeising

The seismic waves revealed rises under Thwaites that are 10 to 20 kilometers long and toothed with blocks of sediment. These blocks stood up to 100 meters tall above the rises and stretched for up to several kilometers horizontally.

The data showed that the upstream faces of these blocks appear to be under greater pressure than their downstream sides, and that there might be layers of deformed ice within the glacier above the rises. Hofstede hypothesizes that the rises and blocks are slowing Thwaites’ flow as its ice presses against them.

Using computers to simulate the flow of Thwaites glacier shows that “it gets hung up on tall features,” said glaciologist Ben Smith of the University of Washington in Seattle, who was not involved in the work.

The rises are probably related to a rift system, an area where tectonic forces have pulled the ground apart, Hofstede said. Under Thwaites, these rifts run roughly perpendicular to the glacier’s ice flow, sort of like speed bumps on a street.

The findings will allow for more nuanced simulations of the glacier’s evolution, Hofstede said, which are crucial for understanding rates of sea level rise. More