THWAITES WILD CARD This unstable glacier-with its potentially disastrous effect on sea levels-is starting to show its hand - Eos.org
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VOL. 101 | NO. 3 Ancient Assyrian Aurorae
MARCH 2020
A Ski Resort Report
New AGU Medalists
THE
THWAITES
WILD CARD
This unstable glacier—with its potentially disastrous
effect on sea levels—is starting to show its hand.
FROM THE EDITOR
Editor in Chief
Heather Goss, AGU, Washington, D.C., USA; Eos_EIC@agu.org
Editorial
The Threat at Thwaites Manager, News and Features Editor
Science Editor
Senior News Writer
Caryl-Sue Micalizio
Timothy Oleson
Randy Showstack
T
News Writer and Production Associate Kimberly M. S. Cartier
he best—or at least most entertaining—thing I learned News and Production Fellow Jenessa Duncombe
from this issue is that glaciers tend to behave “like
Production & Design
pancake batter on a frying pan.” Ted Scambos offers
Manager, Production and Operations Faith A. Ishii
that description in this month’s cover story, “Diagnosing Senior Production Specialist Melissa A. Tribur
Thwaites” (page 18). Editorial and Production Coordinator Liz Castenson
Scambos is the lead scientific coordinator for the U.S. side Assistant Director, Design & Branding Beth Bagley
of the International Thwaites Glacier Collaboration (ITGC). Senior Graphic Designer Valerie Friedman
Graphic Designer J. Henry Pereira
Launched in 2018, this large research initiative hosts eight
teams studying the past, present, and future of Thwaites, one Marketing
of Antarctica’s most unstable glaciers. The problem with Director, Marketing, Branding & Advertising Jessica Latterman
Thwaites, and the West Antarctic region generally, is that it’s Assistant Director, Marketing & Advertising Liz Zipse
Marketing Program Manager Angelo Bouselli
like pancake batter sliding around in too much oil—as it loses
Senior Specialist, Digital Marketing Nathaniel Janick
mass from both above and below, ocean water is creeping in Digital Marketing Coordinator Ashwini Yelamanchili
underneath and reducing the friction between the ice and the bedrock, allowing it to slide
freely over the water. The more it flows, the faster it may calve ice, and scientists have serious Advertising
worries that this will create a runaway situation called marine ice sheet instability. Display Advertising Dan Nicholas
dnicholas@wiley.com
It will not surprise you that a catastrophic collapse at Thwaites could have alarming effects Recruitment Advertising Heather Cain
on sea level rise worldwide. That’s why the ITGC teams are spending four austral summers hcain@wiley.com
drilling into the ice, collecting bedrock samples, and building model after model to help the Science Advisers
experts get a grip on what is happening there. Geomagnetism, Paleomagnetism, Julie Bowles
Of course, there are challenges that come with studying unstable ice at the bottom of the and Electromagnetism
Space Physics and Aeronomy Christina M. S. Cohen
world, and sometimes you must address them by blowing up things in Texas. On page 4 (“Con-
Cryosphere Ellyn Enderlin
trolled Explosions Pave the Way for Thwaites Glacier Research”), read about one of the ITGC Study of the Earth’s Deep Interior Edward J. Garnero
teams trying to study the bedrock underneath the ice. They can “basically create X-ray images Geodesy Brian C. Gunter
of the landscape” by detonating explosives near the surface of the glacier and mapping how History of Geophysics Kristine C. Harper
Planetary Sciences Sarah M. Hörst
the seismic waves propagate, says the lead scientist on the team. If you’d like to learn more
Natural Hazards Michelle Hummel
about how bedrock affects glaciers generally, head to page 13 (“What Lies Beneath Is Import- Volcanology, Geochemistry, and Petrology Emily R. Johnson
ant for Ice Sheets”) to meet some researchers gaining insight into glaciology and ice vulner- Seismology Keith D. Koper
ability by reconstructing the topography under Antarctica back 34 million years. Tectonophysics Jian Lin
Near-Surface Geophysics Juan Lorenzo
Elsewhere in the issue, we hope you’ll turn to page 14 (“Understanding Our Environment
Earth and Space Science Informatics Kirk Martinez
Requires an Indigenous Worldview”) to learn about ice—this time in Alaska—from a different Paleoceanography and Paleoclimatology Figen Mekik
perspective. Raychelle Daniel, of Yup’ik descent, describes the consequences of conducting Mineral and Rock Physics Sébastien Merkel
science and creating science policy without the unique contributions of the Indigenous people Ocean Sciences Jerry L. Miller
Education Eric M. Riggs
immersed in the environment. Daniel’s article was the excellent conclusion of a weeklong
Global Environmental Change Hansi Singh
series of articles on diversity perspectives published at Eos.org. Find the entire series at bit.ly/ Hydrology Kerstin Stahl
Eos-diversity. Tectonophysics Carol A. Stein
See you all next month. Atmospheric Sciences Mika Tosca
Nonlinear Geophysics Adrian Tuck
Hydrology Adam S. Ward
Earth and Planetary Surface Processes Andrew C. Wilcox
Atmospheric and Space Electricity Yoav Yair
GeoHealth Ben Zaitchik
Societal Impacts and Policy Sciences Mary Lou Zoback
©2020. AGU. All Rights Reserved. Material in this issue may be photocopied by
Heather Goss, Editor in Chief individual scientists for research or classroom use. Permission is also granted to use
short quotes, figures, and tables for publication in scientific books and journals. For
permission for any other uses, contact the AGU Publications Office.
Eos (ISSN 0096-3941) is published monthly by AGU, 2000 Florida Ave., NW,
Washington, DC 20009, USA. Periodical Class postage paid at Washington, D.C.,
and at additional mailing offices. POSTMASTER: Send address changes to Member
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Submit your article proposal or suggest a news story to Eos at bit.ly/Eos-proposal.
Views expressed in this publication do not necessarily reflect official positions
of AGU unless expressly stated.
Christine W. McEntee, Executive Director/CEO
EarTh & SPacE ScIENcE NEWS // Eos.org 1
CONTENT
24
28
18 Features
Cover Story 24 Hackathon Speeds Progress
Toward Climate Model
Collaboration
18 Diagnosing Thwaites By Wilbert Weijer et al.
By Javier Barbuzano
Meet the small army of computational scientists who
This Antarctic glacier is rapidly losing mass. An proved 50 heads are better than one.
international team is digging into the ice to figure out
just how bad the situation is.
28 Filling the Gaps
in Ocean Maps
On the Cover
Sledges carry scientific equipment and other supplies during By Xiaoming Liu and Menghua Wang
a full camp move for a project team of the International To complete the picture, this team is figuring out how
Thwaites Glacier Collaboration on 25 December 2019. Credit: the data puzzle pieces fit together.
Joanne Johnson
2 Eos // March 2020
CONTENT
6 14
Columns
From the Editor AGU News
1 The Threat at Thwaites 34 Medalists Honored at AGU’s Fall Meeting 2019
News Research Spotlight
4 Controlled Explosions Pave the Way 48 Reconstructing 150 Million Years of Arctic Ocean Climate
for Thwaites Glacier Research 49 Explaining the Missing Energy in Mars’s Electrons
5 Interstellar Visitors Could Export Terrestrial Life 49 Observational Data Validate Models of Sun’s
to Other Stars Influence on Earth
6 Modern Farming Kick-Starts Large Landslides 50 How Are Microplastics Transported to Polar Regions?
in Peruvian Deserts 51 Improving Estimates of Coastal Carbon Sequestration
7 Here’s What Your Favorite Ski Resort May Look Like 52 Stored Nutrients and Climate Warming
in 2085 Will Feed More Algal Blooms
8 Ancient Assyrian Aurorae Illuminate Solar Activity 52 Timing Matters for Rockfall Estimates
9 The Eternal Nile Is Even More Ancient Than We 53 Modeling the Subsurface Hydrology of the Greenland
Thought Ice Sheet
10 Bikini Seafloor Hides Evidence of Nuclear Explosions
11 Atmospheric Rivers Have Different “Flavors” Positions Available
re-Inca Canal System Uses Hillsides as Sponges
12 P
to Store Water 54 Current job openings in the Earth and space sciences
13 What Lies Beneath Is Important for Ice Sheets
Postcards from the Field
Opinion 57 Teaming up with archaeologists in Florida.
14 Understanding Our Environment Requires
an Indigenous Worldview
16 Integrating Input to Forge Ahead
in Geothermal Research
AmericanGeophysicalUnion @AGU_Eos company/american-geophysical-union AGUvideos americangeophysicalunion americangeophysicalunion
EARTH & SPACE SCIENCE NEWS // Eos.org 3
NEWS
Controlled Explosions Pave the Way
for Thwaites Glacier Research
T
here’s remote, and then there’s Ant- ence Foundation and the United Kingdom’s hot water is necessary to melt the ice, said
arctic remote. Natural Environment Research Council, con- Steven Harder, an explosion seismologist at
Thwaites Glacier, located over 1,500 sists of eight different projects. One of those the University of Texas at El Paso. “The lim-
kilometers from McMurdo Station, falls is Thwaites Interdisciplinary Margin Evolu- itation becomes the amount of fuel you can
squarely in the latter camp. An international tion (TIME), an endeavor to better understand transport to the field.”
collaboration is currently studying this noto- the boundaries (the margins) of the glacier. In 2018, Harder and his colleagues experi-
riously unstable glacier and the significant The size of Thwaites dictates how much ice is mented with another technique, one that
sea level rise that would result from its col- flowing into the sea, said Slawek Tulaczyk, a didn’t require any drilling and had, in fact,
lapse. And recent fieldwork in West Texas, a glaciologist at the University of California, been used in the 1930s in Antarctica. Known
world away, is informing that research. Santa Cruz and lead principal investigator of as Poulter shooting, after Thomas C. Poulter,
Last year, researchers working near the city the TIME project. But because Antarctica is the physicist who developed it, the method
of Tornillo, intentionally detonated a series of blanketed in ice, glaciers are defined only as involves detonating explosives mounted on
explosives mounted atop poles. The shock rivers of ice that flow within slower moving poles above the ground rather than sunk deep
waves created by the detonations sent seismic ice masses, Tulaczyk said. “These boundaries into the ice. Harder and his colleagues exper-
waves into the ground. This technique, known can move. It’s not a very stable situation.” imented with different types of explosives—
as active source seismic, allows scientists to That’s where active source seismic comes ammonium nitrate/fuel oil, ammonium
infer properties of the subsurface based on in. By detonating hundreds of explosives near nitrate/nitromethane, dynamite, and pento-
how those seismic waves propagate. the surface of Thwaites and mapping how the lite, for instance—and metal and bamboo
Later this year, researchers working in seismic signals propagate, it’s possible to poles 1.2, 1.8, and 2.4 meters long.
Antarctica will use this method to study “basically create X-ray images of the land- They worked in remote West Texas in the
Thwaites. Thwaites is currently responsible scape that’s sitting beneath the ice,” said 849,840-hectare University Lands managed
for about 4% of sea level rise worldwide. Some Tulaczyk. That’s important because the mar- by the University of Texas and Texas A&M Uni-
scientists believe that if Thwaites collapsed, gins of Thwaites might be dictated by changes versity systems. “This is a very small part of a
the entire West Antarctic Ice Sheet might in the geology of the subsurface, researchers big project,” said Harder. “It’s trying to figure
destabilize and break apart, boosting sea lev- believe. out how we should do the bigger project.”
els by more than a meter.
Hot Water in a Cold Place Not Too Tall, Not Too Short
The Edges of a River of Ice The traditional way of doing active source The researchers discovered that ammonium
In November 2019, roughly 100 scientists and seismic in Arctic or Antarctic environments n itrate– b ased explosives atop 1.8 - m eter
support staff departed for Antarctica as part involves drilling tens of meters into the ice, metal poles yielded the strongest seismic sig-
of the International Thwaites Glacier Collab- placing an explosive, and detonating it nals. The 1.2-meter poles didn’t give the
oration. (See our cover story on p. 18.) This remotely. But all that drilling is a highly fuel- explosives enough time to fully detonate
consortium, funded by the U.S. National Sci- intensive process because a steady stream of before the shock wave hit the ground, the
team said. And the 2.4-meter poles were too
tall: The gas pressure built up by the detona-
tion was already dropping when the shock
wave hit the surface, Harder and his col-
leagues concluded. These results were pre-
sented at AGU’s Fall Meeting 2019.
In the 2 020–2021 austral summer, TIME
researchers will begin detonating explosives
above Thwaites. Hundreds of seismometers
will pick up the signals, and Tulaczyk and his
colleagues will begin assembling a picture of
the glacier’s extent. There’s a certain irony to
using this technique to study the retreat of
Thwaites, said Tulaczyk, because it was orig-
inally developed by the petroleum industry
for oil and gas exploration. “We’re stealing
their ideas to help alleviate a problem they’ve
created.”
By Katherine Kornei (@k atherinekornei),
Ice cliffs at the northern tip of Thwaites Glacier tower over the Southern Ocean. Credit: Rob Larter Science Writer
4 Eos // March 2020
NEWS
Interstellar Visitors Could Export Terrestrial Life
to Other Stars
L
ife from Earth could spread beyond the single published experiment has identified
solar system if an interstellar visitor them at almost 80 kilometers. That experi-
skimmed our planet’s atmosphere and ment hasn’t been replicated since it was per-
picked up microbial hitchhikers. In fact, formed in 1978. “It’s a somewhat controver-
although the odds are slim, it’s possible Earth sial paper,” Lingam said. That doesn’t mean
has already sent out a slew of these natural the research was wrong, he said, only that it
probes. needed to be independently verified. “Until
Most research on panspermia, the idea that we have another subject that corroborates the
life could be carried from one world to results, we just need to be cautious about
another, focuses on the b lunt-force approach: Visitors like the interstellar comet ‘Oumuamua could using those older studies.”
If a large enough rock slams into a planet help spread life from Earth to other stars. Credit: Siraj didn’t seem overly concerned, point-
infected with life, smaller debris could be ESA/Hubble, NASA, ESO, M. Kornmesser, CC BY 4.0 ing out that his team was mostly interested
blown off world, carrying microorganisms (bit.ly/ccby4-0) in finding out whether the process itself was
into space, where they could eventually col- possible. He expressed optimism that studies
lide with other worlds. But with the recent like his might spur further investigation into
discovery of two interstellar interlopers, how high microorganisms could survive in
‘Oumuamua and Borisov, a new question at up to 50 kilometers above Earth’s surface, the atmosphere.
emerged: Could objects like these have with at least one study identifying them as Hitching a ride is only the first step. Once
scooped up life from Earth’s atmosphere and high as 77 kilometers. For passing comets to microorganisms were outside the solar sys-
carried it back out of the system? pick up a few microbes, higher altitude is bet- tem, radiation from other stars could quickly
It’s possible, according to new research ter because the lower the comet dips, the put an end to any terrestrial life that managed
from Amir Siraj, an undergraduate at Harvard more friction it will encounter and the more to escape the solar neighborhood. That’s why
University, and Harvard theoretical astro- likely it is to burn up without escaping Earth’s comets, both local and interstellar, make
physicist Avi Loeb. Their studies suggest that gravitational grasp. such good transportation. With their icy sur-
objects kicked out of other planetary systems, This not-too-high, not-too-low sweet faces, comets are extremely porous, allowing
as well as long-period comets from our own spot changes with the size and density of the microorganisms to burrow or be pushed into
solar system, could have hit the atmospheric objects. Larger, denser objects could survive the depths rather than ride on the surface.
sweet spot that would allow them to carry a trip through regions lower than their more Tucked away inside, life could be shielded
microorganisms beyond the heliosphere. fragile counterparts. from harmful radiation by its transportation.
“How many objects could have come just Although hitting that sweet spot is unlikely, “It’s hard to know what would happen to
close enough not to hit Earth but just to pick it’s not impossible. Several atmospheric graz- the microbes,” Lingam said, pointing out that
up microbes along the way?” asked Siraj. ing events have been reported since the 1970s, there are few studies on how much protection
Siraj said that he expected the answer to be the most recent being a fireball over the Aus- the icy surface provides from radiation. “If
zero. Instead, his research revealed that as tralian desert in 2017. Such fireballs could they do make it closer to the center of the
many as 50 interstellar objects could have have scooped up life as they passed through. object, deep inside the object, I think they
buzzed Earth during our planet’s lifetime before would be quite fine. It really depends on how
leaving the solar system for good. As many as Escaping the Solar System many of them can burrow to a deeper layer.”
10 long-period comets, born in the solar system Is Just a Start The next step, of course, would be colliding
and freed by the gravitational pull of passing The optimistic upper atmosphere measure- with another habitable planet where the
stars, could also have escaped with life. ments should be taken with caution, warns microorganisms could flourish. Although the
“We’ve sent the Voyager probes,” Siraj Manasvi Lingam, an astrobiologist at the odds of that aren’t covered by the current
said, referring to the 1970s human-made sat- Florida Institute of Technology. Although paper, Siraj said he hopes to study the subject
ellites on their way out of the solar system several studies have found microorganism in the near future.
carrying information about Earth’s life. “But colonies at altitudes of 50 kilometers, only a Impacts remain the dominant method for
in fact, we might have sent thousands of Voy- carrying life off Earth, but Earth-grazing
ager probes already—thousands of rocks that objects could provide a significant addition.
were laden with Earth microbes.” “This is a very small subset, but perhaps one
of the most important,” Siraj said.
Catching a Ride “We might have sent The new research was published in January
in the International Journal of Astrobiology (bit
To pick up terrestrial hitchhikers, a comet
would need to zip through the upper atmo-
thousands of Voyager .ly/earthgrazing-LPC-ISO).
sphere, where microorganisms have been probes already—thousands
detected by other studies, but not dip low
enough to burn up or collide with our planet.
of rocks that were laden By Nola Taylor Redd (@NolaTRedd), Science
Previous studies have found microorganisms with Earth microbes.” Writer
EARTH & SPACE SCIENCE NEWS // Eos.org 5
NEWS
Modern Farming Kick-Starts Large Landslides
in Peruvian Deserts
earth is moving, it will continue to move,
Lacroix said. The cliffs above are feeding the
mechanics of the landslides and promoting
motion farther down, he added.
Paradoxical Impacts
As the slides move downhill, sometimes as
fast as 10 meters a year, they are eating away
at agricultural land in the valleys. Satellite
imagery shows that in the past 4 decades, 7%
of the valley surface has been lost.
The data also show that valuable cropland
on valley plateaus is being eroded as valley
walls crumble. “The paradox is that modern
farming needs extensive irrigation, leading to
landslides, and those landslides destroy the
modern farmland as well as the older farming
areas,” Lacroix said.
Edu Taipe views the Punillo Sur slow moving landslide in the Vitor valley in Peru, which was triggered by irriga- Another group of researchers, led by Paul
tion in the late 1980s. Credit: Pascal Lacroix Santi, a professor of geology and geological
engineering at the Colorado School of Mines
in Golden, is also investigating landslides in
the Siguas valley. One of them could soon
I
n the Vitor and Siguas valleys of south- of these valleys, where rivers provided water have impacts on the Pan-American Highway,
western Peru, giant landslides have been for crops. “But Peruvians wanted to increase a major thoroughfare, and another could
creeping down hillsides for decades, dam- the space for agriculture areas, and they eventually damage an industrial milk facility
aging farmland in the fertile valley basins. For couldn’t do that in the valleys because they that produces approximately half the milk
the first time, scientists have documented the are so narrow,” Lacroix said. “So they started consumed in Peru.
cause of these vast movements of earth: irrigating the plateaus above the valleys.”
large-scale irrigation programs developed to Vast irrigation programs started in the Moving Toward Mitigation
feed modern agriculture on the high plateaus 1950s, and satellite data detailed the expan- Lacroix and Taipe hope their study, published
above. sion of farmland to cover 105 square kilome- in December 2019 in Nature Geoscience, will
“The findings demonstrate the l ong-term ters above the Vitor valley and 76 square kilo- bring the attention of authorities and even-
erosional impacts of irrigation,” said Pascal meters above the Siguas valley. During that tually lead to the deployment of mitigation
Lacroix, a geoscientist based in Grenoble, time, satellite imagery also showed that strategies in the valleys (bit.ly/farming
France, at the Research Institute for Devel- 12 large, slow moving landslides had started, -impacts-ag). The findings show that it is
opment and colead author of the new study. ranging in volume from 20 to 80 million cubic important to use water efficiently, for
“They also highlight the competition meters. The volume of earth moved by the instance, with drip or sprinkler irrigation
between modern and traditional agricul- largest landslide was the equivalent of more with adequate dosing, said hydrologist Wou
ture.” than 26,000 Olympic swimming pools. ter Buytaert of Imperial College London. “The
Lacroix and his collaborator, Edu Taipe of The landslides occurred only on the sides study highlights that rational use of water is
Peru’s Mining and Metallurgical Geological of valleys below irrigated plateaus, and sci- not just a water resources issue but has wider
Institute in Arequipa, visited the valleys in entists found that landslides in the Siguas geomorphological implications,” Buytaert
May 2017, having heard of the landslides and valley began later than those in the Vitor val- said.
their impacts. To investigate further, the ley. This time difference corresponds to later Developing sustainable mitigation strate-
researchers analyzed images from the Satel- development of irrigation programs in the gies requires an understanding of how irriga-
lite pour l’Observation de la Terre (SPOT) 6 region. “The spatial distribution of the land- tion is triggering earth movement. “The only
and SPOT 7 and the Hexagon spy satellite slides, together with the different initiation way to reduce the risk of these disasters is to
taken between 1978 and 2016. timing in the two valleys, clearly indicates investigate the processes,” Taipe said. “With
that the landslides are triggered by irriga- this knowledge, preventative and mitigation
Sleuthing the Culprit tion,” Lacroix said. “And when you go there, measures can be implemented.”
Analyzing the satellite data, the scientists you see water gushing from the cliffs, and it
could see the expansion of cropland on pla- is clearly from irrigation.”
teaus above the valleys. For at least 3 millen- In both valleys, landslides began about By Jane Palmer (@JanePalmerComms), Science
nia, farming had been confined to the basins 20 years after irrigation started, and now that Writer
6 Eos // March 2020
NEWS
Here’s What Your Favorite Ski Resort
May Look Like in 2085
F
or those living in the West, the winter
of 2
014-2015 went down as one of the
worst ski seasons in memory. Snow lev-
els were so low that some ski resorts didn’t
open, whereas others limped along with sub-
par snowpacks. Skiers and snowboarders at
Whistler Blackcomb, a resort in Vancouver,
B.C., rode trams to midmountain to reach
snow.
According to new research from the Uni-
versity of British Columbia, the winter of
2014-2015 may become the new normal.
Climate change could significantly lower A map of ski resorts in the United States and Canada shows the average length of ski seasons from 1971 to
the number of skiable days across western 2000 (left). Model results (right) reveal the decreasing length of ski seasons in 2085 under the high-emission
North America, forcing some ski resorts to scenario. Credit: Michael Pidwirny and Ethan Clark
shut down entirely. The study, which uses
historical data and model projections, fore-
casts that more than 90% of western resorts
will have ski seasons shorter than 120 days by
2085 if countries don’t curb greenhouse gas
countries do not act as aggressively to curb
“I think a lot of people can’t
emissions, and global temperatures soar by
emissions. Although many more severe risks 3°C to 5°C. These scenarios are widely used wrap their heads around
could come from climate change, losing rec-
reational skiing, snowboarding, and snow-
across climate sciences and come from the
Intergovernmental Panel on Climate
what scientists are saying
mobiling opportunities could cost the United Change. about how climate change
States billions of dollars and tens of thou- In the first scenario, only a third of 154 ski
sands of jobs per year, according to the non- resorts have seasons longer than 120 days.
is going to change their
profit Protect Our Winters. Pidwirny said that some researchers regard life.”
“I think a lot of people can’t wrap their 100 days as an economic cutoff for breaking
heads around what scientists are saying about even. In the same scenario, 21 resorts have
how climate change is going to change their zero skiable days, meaning that temperatures
life,” said Michael Pidwirny, an associate pro- never dip below freezing to bring snow.
fessor at the University of British Columbia. In the second scenario, when countries do the research, called the latest study import-
“But a lot of people ski, and a lot of people do little to curb emissions, only 9% of resorts ant and in agreement with other scientific
winter activities.” would pass 120 days, and nearly a third of studies. She said that one way scientists could
“It’s kind of an interesting canary in the resorts wouldn’t have a skiable day all sea- help resorts stay open is by advancing sea-
coal mine,” he added. son. sonal snow forecasts.
Not all ski resorts are affected the same, “Ski resorts are doing their staffing early
Shrinking Seasons however: Resorts in coastal states fare far in the fall, and the ones at lower elevations
Ski resorts need two ingredients for a good worse than those in inland states. In the sec- need information that can let them make the
season: freezing temperatures and a healthy ond scenario, the only resort in Oregon with hard decision of when to either delay opening
dose of precipitation. Pidwirny and his mas- a ski season is Mount Hood, and all resorts in or skip a winter season entirely,” Lundquist
ter’s students Ethan Clark and Kalim Bahba- California have no ski seasons. Yet the higher said.
hani investigated how climate change would temperatures in that scenario help some Ski resorts may welcome the help. If the
jeopardize the necessary conditions for a resorts in interior states like those around the low-snow season of 2014-2015 was any indi-
healthy snowpack. Rocky Mountains because warmer subzero air cation, shortening ski seasons will bleed
First, the researchers calculated baseline can hold more moisture and produce more money from local economies.
air temperatures at 154 ski resorts stretching snow. The team presented its research at AGU’s
from Canada to California using historic “Skiing is in trouble,” Pidwirny said. Fall Meeting 2019 and plans to submit its
weather data. Next, they modeled future Although there is y ear-to-year variability, his results for publication. The project received
mountain temperatures with 15 different prediction for resorts is bleak: “For most of funding from the Canada West Ski Areas
general circulation climate models seeded them, they’ll shut down.” Association.
with two scenarios of future greenhouse gas
concentrations. In one scenario, countries Money Melting Away
curb emissions and cap warming at about 2°C Jessica Lundquist, a professor at the Univer- By Jenessa Duncombe (@jrdscience), Staff
above preindustrial levels; in the other, sity of Washington who was not involved with Writer
EARTH & SPACE SCIENCE NEWS // Eos.org 7
NEWS
Ancient Assyrian Aurorae Illuminate Solar Activity
O
n a dark spring night, the sky blan- several studies have found isotope data of
keting the N eo-Assyrian Empire carbon-14 levels recorded in tree rings that
turned red. The red glow was taken as suggest a strong burst of solar activity during
an ominous sign—one important enough the same time period. By adding Assyrian
that the Assyrian court scribe Issār-šumu- observational evidence to these natural
ēreš carved an official record of the event into archival data, scientists are better able to
a clay tablet. confirm that the event was truly a space
Although the event, which we know today weather event caused by an extreme solar
as the aurora borealis, or northern lights, storm.
wouldn’t have affected the course of nature “Comparing these data from natural
at the time, it is now helping astronomers archives to real historical records made by
understand our Sun and may even help pro- contemporary astrologers at the time is very
tect astronauts and assets in space. important,” said Ilya Usoskin, a space phys-
The Assyrian record is one of the earliest icist at the University of Oulu in Finland who
known observations of aurorae, dating to was not involved with the new research.
around 660 BCE. Aurorae are created by high- “From it, we know that we are on the right
e
nergy particles launched from the Sun, and track, because the two records match each
historical records offer a way to study condi- other.”
tions on the Sun long before the invention of
telescopes. Dangerous Beauty
“Direct observations [of the Sun] span Although solar energetic particles can create
some 400 years with sunspot observations, beautiful aurorae, they can also fry electron-
and ground-based instrument observations ics in telecommunications satellites and
are mostly within 200 years,” said Hisashi harm astronauts in space. The distance from
Hayakawa, lead author of a new study and an the pole to where the ancient Assyrian obser-
astronomer at Osaka University in Japan and This Neo-Assyrian tablet from the Library of Ashur- vations of aurorae were made is similar to
the Rutherford Appleton Laboratory in the banipal provided researchers with what may be one that of an event in 1989 when the power grid
United Kingdom. “To discuss the kind of less of the earliest descriptions of the aurora borealis. in all of Quebec was knocked out.
frequent, but more hazardous events [coming Credit: Trustees of the British Museum, CC BY-NC-SA “It is likely that the [ancient] storms were
from the Sun], we need to expand the data 4.0 (bit.ly/ccbyncsa4-0) considerably large,” Hayakawa said. “Storms
coverage, like with historical documents.” with similar intensity [today] would be harm-
ful to modern technological infrastructures.”
Blasts in the Past Understanding the historical frequency of
Hayakawa and his colleagues identified the Documenting aurorae helps astronomers solar storms and learning how to predict such
records by examining ancient cuneiform tab- understand patterns of solar activity. Mag- big events are important for mitigating their
lets held in the British Museum. These tablets netic storms on the Sun can release giant effects on our t ech-based society. The histor-
were carved by Assyrian court scribes, whose plumes and jets of materials, some of which ical data can help astronomers model how
job was to document important happenings fall back into the Sun and some of which are often such extreme events occur and better
in the empire. They often included accounts ejected and spewed across the solar system. assess the probability of similar extreme
of celestial appearances, like comets (ṣal- Particles that make it to Earth can be funneled events.
lummû), meteors (kakkabu rabû), and lunar along magnetic field lines into Earth’s upper “Direct observations from the last decades
and solar halos (tarbāṣu), which were thought atmosphere, where they strike atmospheric are not very useful here because they just
to be omens of the future. Although most particles, causing them to glow. Red aurorae, cover too short a period of time,” Usoskin
Assyrian and Neo-Assyrian tablets aren’t like the ones seen in ancient Assyria, are typ- said. “Such historical records are very helpful
explicitly dated, their authorship gives schol- ically caused by low-energy electrons. because now we know that during the last,
ars a close idea of when the tablet was writ- Because they follow magnetic field lines, say, 3,000 years, there were three events of
ten—usually within a decade. aurorae are most commonly seen near the that magnitude, which means that on aver-
In the tablets studied, researchers found poles. But strong solar events can make auro- age, we may expect such disasters to occur a
two references from Nineveh (a city near rae visible at lower latitudes. Although today few times per millennia.”
current-day Mosul, Iraq) and one from Baby- it is rare to see an aurora in the Middle East, Hayakawa and his colleagues recently pub-
lon (built along Iraq’s Euphrates River) that 2,000 years ago the magnetic North Pole was lished their analysis of the Assyrian tablets in
describe red aurorae, using terms like akukūtu, much closer to Mesopotamia, hovering over Astrophysical Journal Letters (bit.l y/solar
meaning red glow, or stating, “red covers the the Norwegian archipelago of Svalbard -activity-660-BCE).
sky.” Using the authorship of the tablets, instead of at its current location just 4° south
researchers think the events happened some- of the geographic North Pole.
time between 680 BCE and 650 BCE, a century The newly identified records also match By Mara Johnson- Groh (marakjg@gmail.com),
earlier than previous records of aurorae. indirect evidence of solar activity. Since 2012, Science Writer
8 Eos // March 2020NEWS
The Eternal Nile Is Even More Ancient Than We Thought
I
f you had traveled the length of the Nile tunity to study these interactions on a
River 30 million years ago, you would have l andscape-wide scale.”
followed much the same 6,650-kilometer The team first traced the geologic history
course that you would today. The river has of the Nile by correlating ancient volcanic
been flowing from its headwaters in the Ethi- eruptions in the highlands with massive
opian Highlands to its mouth in the Mediter- deposits of river sediments transported to the
ranean Sea for about 6 times longer than Nile Delta. By combining these observations,
previously thought, its course held steady by the team was able to determine that the Ethi-
deep-mantle currents that mirror the Nile’s opian Highlands rose dramatically around
northward flow. 30 million years ago and have remained rel-
The geological evolution of the Nile River atively unchanged ever since, supported by a
is complicated, said Thorsten Becker, a geo- steady upwelling of hot mantle below the
physicist at the University of Texas at Austin mountain range.
(UT Austin) and coauthor of a new study The researchers then verified their find-
published in Nature Geoscience (bit.ly/ ings using computer modeling to simulate
s
ustaining-Nile-River). At least five ances- the past 40 million years of plate tectonic
tral rivers have flowed north from the Ethi- activity in eastern Africa, an extremely active
opian Highlands since the Miocene. “When region due to the East African Rift system.
the river we now know as the Nile formed The models indicate that a stationary mantle
has been debated for some time,” Becker plume that created the highlands evolved
said. into a sustained south to north flowing con-
Lead author Claudio Faccenna, also at UT veyor belt of mantle that mirrors the south to
Austin, and colleagues took a deeper approach north gradient of the river. The topography
to deciphering the Nile’s ancient history by simulated by the model was “strikingly sim-
connecting the gently tilting landscape along ilar” to the course of the actual Nile, Becker
the river’s course to a conveyor belt of mantle said, down to the locations of the famous Cat-
rock that wells upward in the south under the aracts of the Nile—a series of six rock-choked The new study combines geological field evidence
Ethiopian Highlands and pulls downward on rapids between Khartoum, Sudan, and Aswan, (gathered by Claudio Faccenna, above, and his
the Earth’s crust under the Mediterranean, Egypt. team) with the latest modeling techniques to reveal
keeping the Nile on a consistently northward “This study links a pretty diverse set of new insights into the age of the Nile River. Credit:
course. geologic observations and embeds those find- Claudio Faccenna
ings into a state-of-the-art flow model for
the mantle,” said Eric Kirby, a geophysicist at
Oregon State University who was not involved
in the new study. “It’s a very compelling have occurred more recently than 30 million
The researchers took a combination of techniques.” years ago because the rocky cataracts would
deeper approach to “Over the past decade or two, understand- have been worn down by the powerful river in
ing how the deep Earth influences the sur that much time, he said. “It’s a hard place to
deciphering the Nile’s face has been a burgeoning field,” Kirby said, understand just by looking at the surface
ancient history by “driven by increasingly high resolution seis- expression,” Stern said. “We need to look
mic images and advances in our understand- deeper.”
connecting the gently ing of how to relate seismic images to prop- Becker and colleagues are also planning to
tilting landscape along the erties that govern mantle flow, such as tem- use their new observational and modeling
perature, viscosity, and composition.” techniques to look at mantle activity under
river’s course to a conveyor More work will need to be done to further other large rivers, such as the Congo and
belt of mantle rock. decipher the mysteries of the Nile, said Bob Yangtze. “We’re hoping to develop tech-
Stern, a geoscientist at the University of Texas niques of reading the topography that help us
at Dallas who was not involved in the new fingerprint the underlying d
eep-mantle pro-
study. An interesting next step could involve cesses,” he said. “How does the mantle shape
focusing the new techniques on the Nubian the landscape over time? What are the geo-
The idea that mantle flow patterns can Swell, a region of structural uplift that runs logical and geophysical constraints? These are
influence surface topography is not new, but east to west across the river, creating the Cat- some of the big picture questions we’re trying
the sheer scale of the Nile River drainage aracts of the Nile, Stern said. to answer.”
offers a unique opportunity to study large- “The Nubian Swell is a mysterious area that
s cale surface expressions of this mantle- shows no signs of igneous activity, and yet the
l andscape interaction, Becker said. “Because mantle has to be responsible for that uplift By Mary Caperton Morton (@theblondecoyote),
the river is so long, it offers a unique oppor- somehow,” he said. The uplift also is likely to Science Writer
EARTH & SPACE SCIENCE NEWS // Eos.org 9NEWS
Bikini Seafloor Hides Evidence of Nuclear Explosions
S
eventy-three years after serving as the In contrast, Baker was the world’s first haped plume atop the spray column rained
s
site of the world’s first underwater underwater test of a nuclear weapon. The back down into the crater.
nuclear test, the seafloor around Bikini bomb was anchored 27 meters below the sur- “If you imagine a bathtub, it would be like
Atoll in the Pacific Ocean remains scarred by face of the lagoon and the target fleet. The dumping a giant bag of sand into it,” Trembanis
finely detailed craters and littered with dere- Baker explosion, captured in a series of well- said. “It’s going to hit and then radiate away.”
lict ships. known images, sent nearly 2 million metric
Today an interdisciplinary team of scien- tons of water, sand, and pulverized coral sky- Ghosts of the Past
tists is using sonar to assess the complex sub- ward in a plume over 2 kilometers high. Littered throughout the atoll are the husks of
marine environment. The results provide a decommissioned dreadnoughts, aircraft car-
sobering assessment of humanity’s capacity Milky Mud and Cauliflower Features riers, and submarines situated to bear the
to alter nature. Nuclear testing at Bikini ended in 1958. After brunt of the Able and Baker explosions.
“We’re revealing for the first time the forest so many years, Trembanis brought no expec- In addition to their seafloor mapping,
and the trees of that early dawn of the nuclear tations about what, if anything, he and his which Trembanis describes as “painting the
age,” said Arthur Trembanis, an oceanogra- team might find. house with broad brushstrokes,” the
pher at the University of Delaware who pre- They began by using sonar to “mow the researchers performed detailed assessments
sented his team’s results at AGU’s Fall Meet- lawn,” motoring a tin boat back and forth of the 12 shipwrecks nearest the blast sites.
ing 2019. “Now we can see the configuration across an area 1.5 times the size of New York’s Both explosions sank vessels, flash melt-
of the seabed [around Bikini] and the disposi- Central Park. Altogether, the map represents ing ships into twisted specters. The USS Pilot-
tion of the many ships that were sunk.” 20 million individual points of reflected fish, a submarine close to the Baker blast,
sound, the most detailed geoacoustic map of was built to withstand several hundred kilo
Unleashing the Power of the Atom the region to date. grams per square inch. But pressure sensors
In the aftermath of World War II, the U.S. Navy When scans of the Able site yielded undis- deployed during the test registered pressures
chose Bikini Atoll for a series of controlled turbed seafloor, it seemed time had reclaimed 10 times higher.
nuclear explosions. Between 1946 and 1958, the evidence. But images of the Baker site Following up on the sonar findings, divers
23 confirmed tests were conducted in the area. revealed something unexpected. were sent to six wrecks, and all showed sub-
Trembanis and his team studied Able and Clustering around a laptop, Trembanis and stantial damage that could have come only
Baker, a pair of tests conducted in July 1946 as his team witnessed the r eal-time render from these immense explosions. The Pilotfish
part of Operation Crossroads. Both Able and ing of an underwater crater more than 800 rested on the bottom, its steel rivets torn
Baker involved plutonium fission bombs with meters across—big enough to fit three Roman apart when its hulls breached.
a yield of between 21 and 23 kilotons, but they Colosseums. Even independent of their place in nuclear
were deployed differently. Rather than a smooth bowl, radiating out history, the Pilotfish and other Bikini ship-
The Able test bomb, nicknamed Gilda, was from the center of the Baker crater was a wrecks attest to the l ong-lived effects of
dropped by plane and detonated 150 meters series of what Trembanis called “cauliflower human activities on the environment.
above the lagoon and the target fleet of ships features” embedded in a “powdery, milky As old ships decompose, they become eco-
positioned there. Pressure waves from the mud,” testaments to the blast’s immense logical burdens, and researchers found that
resulting fireball depressed the ocean’s sur- force. He believes these structures formed as several wrecks on the Bikini seafloor are
face and sank several ships. superheated debris from the cauliflower- leaching plumes of oil.
Visible and Invisible Scars
“Mapping the seafloor or shipwrecks isn’t
new,” said Nicole Raineault, chief scientist
with the Ocean Exploration Trust who was not
involved in the study. “But mapping the
impacts of a historical maritime event and
being the first to monitor recovery add some-
thing different.”
According to Trembanis, this study will
serve as an important baseline for monitoring
recovery: “Even though we think of the test-
ing as having ended and gone away, the
impact on both the people and the environ-
ment is still quite visible.”
A geoacoustic map revealed "cauliflower features" on the Bikini seafloor beneath the site of the Baker nuclear test. By Amanda Heidt (@Scatter_Cushion), Science
The unusual bathymetric features were a result of debris that rained down from the cauliflower-shaped plume cre- Writing Graduate Student, University of Califor-
ated by the detonation of Baker's plutonium fission bomb. Credit: Courtesy of Art Trembanis, University of Delaware nia, Santa Cruz
10 Eos // March 2020NEWS
Atmospheric Rivers Have Different “Flavors”
A
tmospheric rivers are wet and windy
by nature—they move vast amounts
of water vapor through the sky in
long, narrow bands. These features, such as
the recurring Pineapple Express events that
carry moisture from around Hawaii to the
West Coast of the United States, often supply
needed precipitation, but they can also bring
flooding rains and damaging winds. Seem-
ingly similar atmospheric rivers, though, can
result in very different amounts of precipita-
tion and wind on land, puzzling scientists and
complicating forecasting efforts.
In new research looking at data from the
past few decades, scientists found that each
atmospheric river comes in one of four “fla-
vors”—wet, windy, wet and windy, or neu-
tral—depending on whether it is moisture
or wind dominated. The new classification
scheme should help researchers discover new An atmospheric river system that drenched parts of California on 14 February 2019 is seen in this image from
insights into how atmospheric rivers affect the National Oceanic and Atmospheric Administration’s GOES-West satellite. Credit: NOAA
weather on the U.S. West Coast and else-
where, according to Katerina Gonzales, a cli-
mate scientist and graduate student at Stan-
ford University. The researchers wanted to find a better way against coastal mountain ranges, causing the
“Different flavors of atmospheric rivers of classifying atmospheric rivers to under- moisture to condense into rain or snow.
have different impacts,” said Gonzales, who stand their diverse behavior. “You need two
presented the research at AGU’s Fall Meeting ingredients to get moisture transport,” Gon- Ingredients for Improving Storm
2019. This realization “could give us better zales said. “We’re losing that nuance when Forecasts
clues for what we’re going to get from future we only look at IVT of atmospheric rivers.” Researchers are realizing that IVT alone is no
storms and climate change.” Gonzales and her team analyzed previously longer enough to understand the behavior
published IVT data for every day that the West of atmospheric rivers, said Gang Chen, an
West Coast Flavors Coast experienced an atmospheric river atmospheric scientist at the University of
Atmospheric rivers are responsible for 30%– between 1980 and 2015. They then parsed the California, Los Angeles who was not involved
40%, on average, of the annual precipitation IVT values into moisture and wind compo- with the new research. “This study in partic-
on the West Coast, with most of this coming nents. When the researchers plotted those ular tries to separate the effects of moisture
from only a few events. Some strong atmo- components against one another, they found and wind…and I think this separation could
spheric rivers carry up to 15 times as much that they could categorize atmospheric rivers be useful” in providing “a better way to look
water as the average flow at the mouth of the with similar IVT values as having high mois- into the total effect” of atmospheric river
Mississippi River. The frequency of atmo- ture and low wind (wet), low moisture and events, Chen said.
spheric river events is expected to increase high wind (windy), high moisture and high Gonzales and her colleagues hope they can
with climate change, according to the U.S. wind (wet and windy), or average levels of use their classifications to forecast the flavors
Global Change Research Program’s Fourth each (neutral). of future atmospheric river events. Prelimi-
National Climate Assessment, released in The researchers also found that “windy” nary data suggest that the windy atmospheric
2017. atmospheric rivers not only showed larger rivers that tend to dump more rain are asso-
Individual atmospheric river events are extremes in surface wind speeds but also ciated with deep troughs of low-pressure
generally characterized using a metric resulted in higher average precipitation both systems offshore, but further research is
called integrated vapor transport (IVT), in the Pacific Northwest and in California. required to build predictive models. She said
which accounts for water volumes and Gonzales said she was surprised by the she imagines a future in which water manag-
winds to assess the total amount of water result at first. “I would have expected the ers and public safety officials can be warned
vapor moving through the atmosphere in a moisture-dominant atmospheric rivers to further in advance of when such storms are
river. But it is not uncommon for storms [result in] more precipitation,” Gonzales expected to hit land.
with similar IVT values to have different said. But she now thinks that “wet” storms
impacts on land in terms of precipitation may actually be “wind limited” and that
and wind speeds, which could be the differ- “moisture is allowed to see its full potential” By Ariana Remmel (@science_ari), Science Writ-
ence between muggy rains and dry, bluster- as precipitation in wind-dominant atmo- ing Graduate Student, University of California,
ing gales. spheric rivers when clouds are forcibly blown Santa Cruz
EARTH & SPACE SCIENCE NEWS // Eos.org 11NEWS
Pre-Inca Canal System Uses
Hillsides as Sponges to Store Water
L
ima, Peru, which lies on the dry Pacific are examining techniques already used by
side of the Andes Mountains, is the Indigenous cultures around the world. But
second-largest desert city in the world. few studies quantify the hydrological effects
(Cairo, Egypt, is the largest.) To endure the of natural interventions like those used by
region’s 7- to 9-month dry season, Lima’s Indigenous Andean mountain communities. The village of Huamantanga in the Peruvian Andes
10 million inhabitants are almost entirely “Sometimes we think that scientific continues to use and maintain 1,400-year-old amu-
reliant on water collected from the glaciated knowledge is more valuable than Indigenous nas, canals that preserve water, to collect and store
Andes or transported from the lush Amazon and ancient knowledge,” Ochoa-Tocachi said. water during the long dry season. Credit: Diego
rain forest to the east. But the glaciers are “With this research, we tried to really show Pérez/Forest Trends
melting, and existing dams and reservoirs, how both can complement each other.”
which hold a total of 330 million cubic meters
of water, can quench Lima’s thirst through Going with the Flow
only a single year of drought. choa-Tocachi and his team conducted work-
O the dry season. These effects could increase
A team of hydrologists, engineers, and shops, field visits, and interviews with over the capacity of current gray infrastructure to
social scientists is hoping to strengthen the 100 members of a village called Huamantanga withstand drought conditions.
water security of Lima and other Peruvian cit- “The beauty of Indigenous knowledge is in
ies through analysis of a 1,4 00-year-old its specificity,” said Kate Brauman, lead sci-
nature-based system developed by pre-Inca entist for the Global Water Initiative at the
mountain communities. The technique uses University of Minnesota’s Institute on the
a canal system that diverts water from
“Sometimes we think that Environment, who was not involved in the
streams to small ponds or spreads it over scientific knowledge is study. “Indigenous knowledge of water man-
rocky hillslopes that act as natural sponges. agement is particularly beneficial because it’s
This slows the flow of water down the moun-
more valuable than closely tied to the place where it was devel-
tains, preserving it into the dry season. Indigenous and ancient oped, and it’s been honed to be very respon-
The team’s analysis determined that if the sive to local conditions.”
system were scaled up to its maximum capac- knowledge. With this Ochoa-Tocachi is hoping that his team’s
ity, it could divert, infiltrate, and recover up to research, we tried to really findings will help to inform policy decisions
100 million cubic meters of water and increase in the region as melting glaciers remove a
the region’s dry-season water volume by up show how both can previously relied upon natural buffer. “If the
to 33%. Lead author Boris O choa-Tocachi of complement each other.” glaciers are retreating, the only way to coun-
Imperial College London presented the team’s teract the loss of this buffer is through the use
findings at AGU’s Fall Meeting 2019. of natural infrastructure,” he said.
Peru has embraced green infrastructure in
Quantifying the Benefit recent years, but the projects that receive
of Green Infrastructure in the Andean Highlands near Lima. The vil- funding aren’t always backed by evidence.
Like most modern cities, Lima relies on gray lage is one of the last to maintain the water- For instance, a recent review paper coau-
infrastructure like reservoirs and dams for saving canals known as amunas, and the team thored by Ochoa-Tocachi found that a policy
water diversion and storage. Gray infrastruc- was able to locate 11 operational infiltration of planting nonnative trees in high-altitude
ture alone, however, has its drawbacks. It is canals through participatory mapping. native grassl ands is actually decreasing,
often expensive and challenging to imple- Then they injected a red dye into one of the rather than increasing, water availability
ment. It also has a static threshold, being canals to track the water’s progress over time. (bit.ly/restore-forest-cover). This year, he
unable to adapt to shifting environmental Samples from local springs showed that water and his team will begin a review of the ben-
conditions. from the canal was retained underground for efits of native grasses for water security and
Natural (green) infrastructure can be much between 2 weeks and 8 months, which means erosion prevention to incentivize their pres-
more dynamic and cost-effective than gray that at least some of it was stored for the ervation.
infrastructure. Green infrastructure is a broad entirety of the dry season. “The work that Dr. Ochoa-Tocachi and his
category that can include planting native Once they had quantified the capacity of team are doing is critical because we need
grasses to prevent erosion and maintaining existing amunas, the researchers modeled more robust evidence of exactly how effective
wetland health to hold and filter water. Cru- what it might look like to upscale the system green infrastructure is, and under which con-
cially, communities can use it in addition to and apply it to the Rímac River basin, one of ditions,” Brauman said.
the dams and reservoirs already in place, Lima’s primary water sources. They deter-
amplifying their effectiveness and providing mined that 35% of the water flowing through
a buffer when their threshold is exceeded. the Rímac River during the wet season could By Rachel Fritts (@rachel_fritts), Science Writ-
To understand the most effective ways to be similarly diverted, increasing the river’s ing Graduate Student, Massachusetts Institute
implement green infrastructure, researchers dry-season flow by 33% at the beginning of of Technology, Cambridge
12 Eos // March 2020You can also read
