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