As much as 50% of the plume shooting out of geysers on Saturn’s moon Enceladus could be ice, scientists reported at the AGU conference. Read the full story here.

New US Geological Survey director Marcia McNutt talked with Nature this week about her priorities in the job. Read the full interview here.

Footage of an eruption nearly 1,200 metres under the sea was unveiled this week at the AGU meeting. The 50-plus hours of high-definition film, complete with background sound, represent one of the first times that lava has been caught flowing on the deep sea floor. Read the full story here.

Temperatures on the Moon are cold enough to freeze nitrogen, according to new findings from the Lunar Reconnaissance Orbiter. Read the full story here.

The morning of September 29, 2009, was one Mase Akapo will never forget.

Akapo is a meteorologist with the National Weather Service in Pago Pago, American Samoa, and one of his jobs is to help prepare the islands for natural disasters. At 6:48 a.m. that day, he felt the ground shaking stronger than he’d ever felt before. When you’re an emergency manager, that means just one thing: get to work. Ten minutes later he was pulling into his office, where a local radio station was already on the phone asking if a tsunami was on the way.

Preliminary magnitudes for the quake were also rolling in: 7.1, then 7.9. (It was later revised upward to 8.0 on the moment magnitude scale.) “I couldn’t believe it was so strong,” says Akapo – and thus he figured it must have come from the nearby Tonga trench, where one tectonic plate dives beneath another, triggering powerful earthquakes in the process. The trench is only 250 kilometers from Pago Pago.

Tsunamis sometimes provide a fair amount of warning that they’re coming: if you’re in Hawaii, for instance, and a quake hits off Japan you have hours to prepare. But if a large quake strikes virtually right under your feet, you might only have 15 minutes to figure out how to get to high ground.

Akapo sprang into gear, issuing a tsunami warning and contacting the Department of Homeland Security to active an emergency alert that went out at 7:02 a.m. If that sounds efficient, it’s only due to lots of preparation; in a tsunami drill months earlier, emergency managers encountered congested phone lines and instead issued two-way handheld radios. The day the tsunami actually struck, those radios were the only way for managers to reach each other.

As evacuations go, American Samoa was a success story, Akapo says. In one school, for instance, 100 children were sitting down to eat breakfast when they felt the shaking. They sprang up, guided by their teachers, and quickly and efficiently evacuated to higher ground, along with the entire village. All were spared.

More than 100 other people died in the 29 September tsunami, but many more could have been killed. The key is repetition and public education, Akapo says. American Samoa, for instance, holds disaster preparedness drills every September. I asked him if people get tired of all the repetitive messages of impending doom. Yes, he replied – “people always say, here comes Mr. Tsunami again”.

But early one day in September, all those drills with Mr. Tsunami paid off.

Image: Vasily Titov

I’d be remiss in not mentioning that my freelance colleague Harvey Leifert is blogging climate topics from AGU for our sister site Nature Reports Climate Change, here. And don’t miss their coverage of the Copenhagen negotiations; the site’s editor Olive Heffernan is there, as is my Nature colleague Jeff Tollefson.

It’s a busy week for the earth sciences all around! Many researchers here at AGU have just gotten back from Copenhagen, or are heading there shortly.

Chalk up another piece of dire news for the Arctic in a globally warmed future. Researchers have identified a previously unknown climate feedback effect suggesting that, as vegetation creeps northward, it will accelerate warming trends already in place.

Read the full story on Nature News here.

The GRACE gravity-hunting satellites have nailed another significant observation: Groundwater levels in California’s agriculturally rich Central Valley have dropped dramatically since 2003.

GRACE is a pair of satellites that zoom constantly around Earth, the distance between them varying a tiny bit as underlying gravity – say, a big mountain range – tugs the leading satellite ahead ever so slightly. The mission, a joint effort of NASA and the German Aerospace Center, has made fundamental discoveries about how quickly the Greenland and Antarctic ice sheets are losing mass, and about groundwater depletion in regions such as India.

At the AGU meeting today, Jay Famiglietti of the University of California, Irvine, presented new numbers on California, which has been suffering through a drought since 2006. GRACE data show that over a period of 66 months, the water stored in the basins of the Sacramento and San Joaquin rivers, which together cover 154,000 square kilometers, decreased by more than 31 cubic kilometers – nearly the volume of the massive Lake Mead reservoir. Of that, nearly two-thirds, or 20 cubic kilometers, could be attributed to groundwater loss from the Central Valley.

“That’s a ton of water,” says Famiglietti, “and it has huge implications.” The Valley produces more than 250 different agricultural crops and accounts for one-sixth of the irrigated land in the United States.

Further monitoring by GRACE may help improve drought predictions for the state and help regional managers better handle their ever-scarcer water resources, he says.

Image: NASA

Change is in the air this year at the fall American Geophysical Union meeting, and not just because of the gossip in the hallways about what might happen at the climate negotiations in Copenhagen this week.

No, the AGU changes are far more navel-gazing and concern the future of the 50,000-member society itself. Last year its longtime executive director Fred Spilhaus said he would step down; this fall the society launched an extensive soul-searching exercise to not only identify the next executive director but also re-evaluate AGU’s overall mission. Consultants have been busy canvassing members for opinions (full disclosure: as a lapsed member and media representative, I participated in one of these interviews) and the lobby of the Moscone West conference center is now decorated with perky graphic posters full of ideas generated during these brainstorming sessions.

It’ll be interesting to see where all this internal scrutiny leads the society. Like other major scientific organization, it built itself up to a position of strength and influence over the past few decades, but is now struggling to figure out its future in a changing media and scientific landscape.

Judging by the buzz in the hallways and the youth and enthusiasm of the members coursing through Moscone this week, it shouldn’t be too hard to come up with an answer.

Cities often take a lot of heat in environmental discussions. All that pavement and pollution damages human lungs and warms the climate. But a few sessions this week suggest that cities may be part of the greenhouse solution.

First a few challenges: Cities are carbon bombs. In the United States, urban areas cover less than 3 percent of the land area but account for 70 to 80 percent of the carbon dioxide emitted by fossil fuel burning. And cities are growing. By 2030, 60 percent of the world population will be urbanites.

Now some of the good news: Cities are carbon vaults. They and other human settlements store a surprising amount of carbon—to the tune of 18 petagrams in the United States. That’s almost 10 percent of the total land carbon storage in the conterminous US, according to Galina Churkina of the Max-Planck Institute for Biogeochemistry in Germany. The carbon is locked in everything from landfills to the books lining library shelves.

Question: What has a higher carbon density—a city or a tropical forest?

Answer after the jump.

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