Groundwater pumping leads to sea level rise, cancels out effect of dams

As people pump groundwater for irrigation, drinking water, and industrial uses, the water doesn’t just seep back into the ground – it also evaporates into the atmosphere, or runs off into rivers and canals, eventually emptying into the world’s oceans. This water adds up, and a new study calculates that by 2050, groundwater pumping will cause a global sea level rise of about 0.8 millimeters per year.

“Other than ice on land, the excessive groundwater extractions are fast becoming the most important terrestrial water contribution to sea level rise,” said Yoshihide Wada, with Utrecht University in the Netherlands and lead author of the study. In the coming decades, he noted, groundwater contributions to sea level rise are expected to become as significant as those of melting glaciers and ice caps outside of Greenland and the Antarctic.

Between around 1970 and 1990, sea level rise caused by groundwater pumping was cancelled out as people built dams, trapping water in reservoirs so the water wouldn’t empty into the sea, Wada said. His research shows that starting in the 1990s, that changed as populations started pumping more groundwater and building fewer dams.

The researchers looked not only at the contribution of groundwater pumping, which they had investigated before, but also at other factors that influence the amount of terrestrial water entering the oceans, including marsh drainage, forest clearing, and new reservoirs. Wada and his colleagues calculate that by mid-century, the net effect of these additional factors is an additional 0.05 mm per year of annual sea level rise, on top of the contribution from groundwater pumping alone.

The research team’s article is being published today in Geophysical Research Letters, a journal of the American Geophysical Union.

The last report of the United Nations Intergovernmental Panel on Climate Change in 2007 addressed the effect on sea level rise of melting ice on land, including glaciers and ice caps, Wada said. But it didn’t quantify the future contribution from other terrestrial water sources, such as groundwater, reservoirs, wetlands and more, he said, because the report’s authors thought the estimates for those sources were too uncertain.

“They assumed that the positive and negative contribution from the groundwater and the reservoirs would cancel out,” Wada said. “We found that wasn’t the case. The contribution from the groundwater is going to increase further, and outweigh the negative contribution from reservoirs.”

In the current study, the researchers estimated the impact of groundwater depletion since 1900 using data from individual countries on groundwater pumping, model simulations of groundwater recharge, and reconstructions of how water demand has changed over the years. They also compared and corrected those estimates with observations from sources such as the GRACE satellite, which uses gravity measurements to determine variations in groundwater storage.

With these groundwater depletion rates, Wada and his colleagues estimate that in 2000, people pumped about 204 cubic kilometers (49 cubic miles) of groundwater, most of which was used for irrigation. Most of this, in turn, evaporates from plants, enters the atmosphere and rains back down. Taking into account the seepage of groundwater back into the aquifers, as well as evaporation and runoff, the researchers estimated that groundwater pumping resulted in sea level rise of about 0.57 mm in 2000 – much greater than the 1900 annual sea level rise of 0.035 mm.

The researchers also projected groundwater depletion, reservoir storage, and other impacts for the rest of the century, using climate models and projected population growth and land use changes. The increase in groundwater depletion between 1900 and 2000 is due mostly to increased water demands, the researchers find. But the increase projected between 2000 and 2050 is mostly due to climate-related factors like decreased surface water availability and irrigated agricultural fields that dry out faster in a warmer climate.

If things continue as projected, Wada estimates that by 2050, the net, cumulative effect of these non-ice, land-based water sources and reservoirs — including groundwater pumping, marsh drainage, dams, and more — will have added 31 mm to sea level rise since 1900.

The new study assumes that, where there is groundwater, people will find a way to extract it, Wada said, but some of his colleagues are investigating the limits of groundwater extraction. One way to decrease groundwater’s contribution to sea level rise, he noted, is to improve water efficiency in agriculture — to grow more with less groundwater.

Visiting snowball Earth

Ancient glacial deposits in Norway (snowball Earth-aged Smalfjord and the younger Mortensnes formations) are superbly documented and illustrated in this comprehensive eight-day field guide. This guide was written specifically for use in the field, and, as authors A.H.N. Rice, Marc B. Edwards, and T.A. Hansen note, “is not necessarily fully understandable without actually being in front of the rocks.” However, all readers will find the guide a fascinating peek into a wondrous, ancient Snowball Earth.

The aim of the authors (A.H.N. Rice from the University of Vienna; Marc B. Edwards of Houston, Texas, USA; and T.A. Hansen of Talisman Energy Norge AS) is to provide detailed coverage of both the typical and the atypical lithologies and sedimentary structures in the glacial deposits in Finnmark, northern Norway. The guide, they note, is not a systematic update on published ideas and interpretations, although this has been done at some outcrops. Instead, the authors invite readers “to critically evaluate our interpretations in the field and to publish their own ideas.”

The area is a treasure-trove of geologic features. Lodgement, banded, deformation, flow and melt-out diamictites derived from gneissic, clastic, and dolomitic sources are described, as well as glaciomarine, proglacial and fluvioglacial sediments. Outcrops showing glaciotectonic folds, faults, flanking structures, shear-sense criteria (sigma-clasts), fluidized sediments, pro- and sub-glacial channels, iceberg dump structures, ghost clasts, dropstones, ice-crystal molds, and a kettle-hole are included. The classic glacial striations at Oaibaččanjar’ga are described in detail. Marinoan cap-dolostones overlying the Smalford Formation are also included. More than 60 illustrations complete this guide.

Logistically, Finnmark is easily accessible by airplane and/or car in comparison to other Neoproterozoic glacial successions. Most outcrops are along the roadside or are easily reached by small boats. The book includes information about accommodations and renting small boats, as well as a summary of the natural and local history.

Finnmark lies well north of the Arctic Circle and thus has 24 hours of daylight during the midsummer months. The midnight sun disappears around 28 July in the Tana area, although it remains light throughout the night for a week or more afterward. However, nighttime temperatures rapidly drop in August, and a ground frost is not unusual in the first week of that month. Better weather is more likely in late June to early July, and this is the recommended time for an excursion.

This excursion was first run as part of the International GeoscienceProgramme (IGCP) 512 “Neoproterozoic Ice Ages” project during the 33rd International Geological Congress, in Oslo, Norway, in 2008.

Analysis of speed of Greenland glaciers gives new insight for rising sea level

The north branch of Jakobshavn Isbrae is in the upper left corner of the image, with several newly calved icebergs in front of it. The larger, faster moving, south branch is located near the upper right corner. Prior to about 2003, both branches merged to create a large floating ice tongue that extended beyond the iceberg covered area visible in this image. Since the 1990, the glacier calving front (terminus) has retreated about 18 km. Now, it is only in the winter that both branches sometimes merge to form a much smaller seasonal ice tongue, which breaks up in the spring. -  Polar Science Center, Applied Physics Laboratory, University of Washington
The north branch of Jakobshavn Isbrae is in the upper left corner of the image, with several newly calved icebergs in front of it. The larger, faster moving, south branch is located near the upper right corner. Prior to about 2003, both branches merged to create a large floating ice tongue that extended beyond the iceberg covered area visible in this image. Since the 1990, the glacier calving front (terminus) has retreated about 18 km. Now, it is only in the winter that both branches sometimes merge to form a much smaller seasonal ice tongue, which breaks up in the spring. – Polar Science Center, Applied Physics Laboratory, University of Washington

Changes in the speed that ice travels in more than 200 outlet glaciers indicates that Greenland’s contribution to rising sea level in the 21st century could be significantly less than the upper limits some scientists thought possible.

The finding comes from a paper funded by the National Science Foundation (NSF) and NASA and published in today’s journal Science.

While the study indicates that a melting Greenland’s contributions to rising sea levels could be less than expected, researchers concede that more work needs to be done before any definitive trend can be identified.

Studies like this one are designed to examine more closely and in greater detail what is actually happening with the ice sheets, often using newer and more precise tools and thereby better defining the parameters that scientists use to make predictions, such as the upper limits of sea-level rise.

“This study provides more evidence that the rate at which these glaciers can dump ice into the ocean is indeed limited,” said Ian Howat, assistant professor of Earth sciences and member of the Byrd Polar Research Center at Ohio State University, a co-author on the paper. “What remains to be seen is how long the acceleration will continue–but it appears that our worst-case scenarios aren’t likely.”

The fate of the Earth’s ice sheets and their potential contributions to sea-level rise as the globe warms are among the major scientific uncertainties cited in the Fourth Assessment of the Intergovernmental Panel on Climate Change (IPCC). This is in part because the Greenland and Antarctic ice sheets have historically been, and in large measure continue to be, relatively sparsely monitored, as compared to other parts of the globe.

The faster the glaciers move, the more ice and melt water they release into the ocean.

In previous studies, scientists trying to understand the contribution of melting ice to rising sea level in a warming world considered a scenario in which the Greenland glaciers would either double or increase by as much as ten-fold their velocity between 2000 and 2010 and then stabilize at the higher speed.

This new study shows Greenland ice would likely move at the lower rate–a doubling of its speed–and contribute about four inches to rising sea level by 2100. The previous studies used the higher speed and estimated the glaciers would contribute nearly 19 inches by the end of this century.

In the new study, the scientists extracted a decade-long record of changes in Greenland outlet glaciers by producing velocity maps using data from the Canadian Space Agency’s Radarsat-1 satellite, Germany’s TerraSar-X satellite and Japan’s Advanced Land Observation Satellite. They started with the winter of 2000-01 and then repeated the process for each winter from 2005-06 through 2010-11 and found that the outlet glaciers had not increased in velocity as much as had been speculated.

“So far, on average we’re seeing about a 30 percent speedup in 10 years [of Greenland glaciers, which gives new insight for rising sea level],” said Twila Moon, a University of Washington doctoral student in Earth and space sciences and lead author of the paper documenting the observations.

“This study is a great example of the power of high-resolution data sets in both space and time, and the importance of looking carefully at as much data as possible in helping make the best predictions we can of future changes”, said Henrietta Edmonds, program director for Arctic Natural Sciences in NSF’s Office of Polar Programs.

The scientists saw no clear indication in the new research that the glaciers will stop gaining speed during the rest of the century, and so by 2100 they could reach or exceed the scenario in which they contribute four inches to sea level rise.

The record showed a complex pattern of behavior. Nearly all of Greenland’s largest glaciers that end on land move at top speeds of 30 to 325 feet a year, and their changes in speed are small because they are already moving slowly. Glaciers that terminate in fjord ice shelves move at 1,000 feet to a mile a year, but didn’t gain speed appreciably during the decade.

In the East, Southeast and Northwest areas of Greenland, glaciers that end in the ocean can travel seven miles or more in a year. Their changes in speed varied (some even slowed), but on average the speeds increased by 28 percent in the Northwest and 32 percent in the Southeast during the decade.

Moon said she was drawn to the research from a desire to take the large store of data available from the satellites and put it into a usable form to understand what is happening to Greenland’s ice. “We don’t have a really good handle on it and we need to have that if we’re going to understand the effects of climate change,” she said. “We are going to need to continue to look at all of the ice sheet to see how it’s changing, and we are going to need to continue to work on some tough details to understand how individual glaciers change.”

GPS on commercial ships could improve tsunami warnings

While in transit from Hawaii to Guam, the research vessel Kilo Moana detected the February 2010 Chilean tsunami. -  University of Hawaii, SOEST
While in transit from Hawaii to Guam, the research vessel Kilo Moana detected the February 2010 Chilean tsunami. – University of Hawaii, SOEST

Commercial ships travel across most of the globe and could provide better warnings for potentially deadly tsunamis, according to a study published May 5 by scientists at the University of Hawaii – Manoa (UHM) and the National Oceanic and Atmospheric Administration’s Pacific Tsunami Warning Center.

James Foster, lead author and Assistant Researcher at the UH School of Ocean and Earth Science and Technology (SOEST), and colleagues were able to detect and measure the properties of the tsunami generated by the magnitude 8.8 earthquake in Maule, Chile (February 2010), even though, out in the open ocean, the wave was only about 4 inches (9.4 cm) high. The UH research vessel Kilo Moana was on its way from Hawaii to Guam at the time of the tsunami, and was equipped with geodetic GPS system recording data as the tsunami passed by.

Careful analysis of this data showed that the researchers were able to detect changes in the sea-surface height very similar to the Pacific Tsunami Warning Center predictions. This finding came as a surprise because tsunamis have such small amplitudes in the deep water, in contrast to their size when they reach the coastline, that it seemed unlikely that the tsunami would be detected using GPS unless the ship was very close to the source and the tsunami was very big. “Our discovery indicates that the vast fleet of commercial ships traveling the ocean each day could become a network of accurate tsunami sensors,” Foster said.

Although the initial warning for a tsunami is based on seismic data from the earthquake, the details about whether a tsunami was actually generated, how big it is, and where the energy is directed are currently provided by tide gauges and deep ocean pressure sensors (DART system). This is the information that is needed to accurately predict how big the tsunami will be for specific locations, and whether or not an evacuation, and the associated cost, is necessary. Tide gauges are restricted to land and therefore are sparsely distributed, while the DART systems are very expensive and hard to maintain. Consequently, during the 2010 Chilean earthquake, the DART sensor closest to Hawaii was out of order. In fact, nearly 30% of that network was down at the time.

Commercial shipping lines, however, run all around the Pacific basin and provide great coverage globally around tsunamigenic regions (areas of the Earth that produced tsunamis). “If we could equip some fraction of the shipping fleet with high-accuracy GPS and satellite communications, we could construct a dense, low-cost tsunami sensing network that would improve our detection and predictions of tsunamis — saving lives and money,” Foster commented. Foster and co-authors estimate that this sort of ship-based system would have been able to detect the 2004 Indian Ocean tsunami within an hour, potentially save thousands of lives.

Foster and fellow SOEST researchers plan to deploy a demonstration system which will stream GPS data from one or two ships, thus generating accurate real-time heights and confirming that this approach can achieve the accuracy needed for tsunami detection. As a bonus, the same processing system will generate data that meteorologists can use to improve weather forecasts.

Increasing speed of Greenland glaciers gives new insight for rising sea level

These icebergs recently calved from the front of the north branch of Jakobshavn Isbrae, a large outlet glacier that drains 6.5 percent of the Greenland ice sheet. The fact that they are upright, indicated by their dirty and crevassed surfaces, suggests they calved from the floating end of a glacier. -  Ian Joughin/University of Washington
These icebergs recently calved from the front of the north branch of Jakobshavn Isbrae, a large outlet glacier that drains 6.5 percent of the Greenland ice sheet. The fact that they are upright, indicated by their dirty and crevassed surfaces, suggests they calved from the floating end of a glacier. – Ian Joughin/University of Washington

Changes in the speed that ice travels in more than 200 outlet glaciers indicates that Greenland’s contribution to rising sea level in the 21st century might be significantly less than the upper limits some scientists thought possible, a new study shows.

“So far, on average we’re seeing about a 30 percent speedup in 10 years,” said Twila Moon, a University of Washington doctoral student in Earth and space sciences and lead author of a paper documenting the observations published May 4 in Science.

The faster the glaciers move, the more ice and meltwater they release into the ocean. In a previous study, scientists trying to understand the contribution of melting ice to rising sea level in a warming world considered a scenario in which the Greenland glaciers would double their velocity between 2000 and 2010 and then stabilize at the higher speed, and another scenario in which the speeds would increase tenfold and then stabilize.

At the lower rate, Greenland ice would contribute about four inches to rising sea level by 2100 and at the higher rate the contribution would be nearly 19 inches by the end of this century. But the researchers who conducted that study had little precise data available for how major ice regions, primarily in Greenland and Antarctica, were behaving in the face of climate change.

In the new study, the scientists created a decadelong record of changes in Greenland outlet glaciers by producing velocity maps using data from the Canadian Space Agency’s Radarsat-1 satellite, Germany’s TerraSar-X satellite and Japan’s Advanced Land Observation Satellite. They started with the winter of 2000-01 and then repeated the process for each winter from 2005-06 through 2010-11, and found that the outlet glaciers had not increased in velocity as much as had been speculated.

“In some sense, this raises as many questions as it answers. It shows there’s a lot of variability,” said Ian Joughin, a glaciologist in the UW’s Applied Physics Laboratory who is a coauthor of the Science paper and is Moon’s doctoral adviser.

Other coauthors are Benjamin Smith of the UW Applied Physics Laboratory and Ian Howat, an assistant professor of earth sciences at Ohio State University. The research was funded by NASA and the National Science Foundation.

The scientists saw no clear indication in the new research that the glaciers will stop gaining speed during the rest of the century, and so by 2100 they could reach or exceed the scenario in which they contribute four inches to sea level rise.

“There’s the caveat that this 10-year time series is too short to really understand long-term behavior,” Howat said. “So there still may be future events – tipping points – that could cause large increases in glacier speed to continue. Or perhaps some of the big glaciers in the north of Greenland that haven’t yet exhibited any changes may begin to speed up, which would greatly increase the rate of sea level rise.”

The record showed a complex pattern of behavior. Nearly all of Greenland’s largest glaciers that end on land move at top speeds of 30 to 325 feet a year, and their changes in speed are small because they are already moving slowly. Glaciers that terminate in fjord ice shelves move at 1,000 feet to a mile a year, but didn’t gain speed appreciably during the decade.

In the east, southeast and northwest areas of Greenland, glaciers that end in the ocean can travel seven miles or more in a year. Their changes in speed varied (some even slowed), but on average the speeds increased by 28 percent in the northwest and 32 percent in the southeast during the decade.

“We can’t look at one glacier for 100 years, but we can look at 200 glaciers for 10 years and get some idea of what they’re doing,” Joughin said.

Moon said she was drawn to the research from a desire to take the large store of data available from the satellites and put it into a usable form to understand what is happening to Greenland’s ice.

“We don’t have a really good handle on it and we need to have that if we’re going to understand the effects of climate change,” she said.

“We are going to need to continue to look at all of the ice sheet to see how it’s changing, and we are going to need to continue to work on some tough details to understand how individual glaciers change.”

Researchers use stalagmites to study past climate change

Stalagmites like these from northern Borneo are the ice cores of the tropics. -  Adkins/Caltech
Stalagmites like these from northern Borneo are the ice cores of the tropics. – Adkins/Caltech

There is an old trick for remembering the difference between stalactites and stalagmites in a cave: Stalactites hold tight to the ceiling while stalagmites might one day grow to reach the ceiling. Now, it seems, stalagmites might also fill a hole in our understanding of Earth’s climate system and how that system is likely to respond to the rapid increase in atmospheric carbon dioxide since preindustrial times.

Many existing historical climate records are biased to the high latitudes- coming from polar ice cores and North Atlantic deep ocean sediments. Yet a main driver of climate variability today is El Niño, which is a completely tropical phenomenon. All of this begs the question: How do we study such tropical climate influences? The answer: stalagmites.

“Stalagmites are the ice cores of the tropics,” says Jess Adkins, professor of geochemistry and global environmental science at the California Institute of Technology (Caltech). He and geochemist Kim Cobb of the Georgia Institute of Technology led a team that collected samples from stalagmites in caves in northern Borneo and measured their levels of oxygen isotopes to reconstruct a history of the tropical West Pacific’s climate over four glacial cycles during the late Pleistocene era (from 570,000 to 210,000 years ago).

The results appear in the May 3 issue of Science Express. The lead author of the paper, Nele Meckler, completed most of the work as a postdoctoral scholar at Caltech and is now at the Geological Institute of ETH Zürich.

Throughout Earth’s history, global climate has shifted between periods of glacial cooling that led to ice ages, and interglacial periods of relative warmth, such as the present. Past studies from high latitudes have indicated that about 430,000 years ago-at a point known as the Mid-Brunhes Event (MBE)-peak temperatures and levels of atmospheric carbon dioxide in interglacial cycles were suddenly bumped up by about a third. But no one has known whether this was also the case closer to the equator.

By studying the records from tropical stalagmites, Adkins and his team found no evidence of such a bump. Instead, precipitation levels remained the same across the glacial cycles, indicating that the tropics did not experience a major shift in peak interglacial conditions following the MBE. “The stalagmite records have glacial cycles in them, but the warm times-the interglacials-don’t change in the same way as they do at high latitudes,” Adkins says. “We don’t know what that tells us yet, but this is the first time the difference has been recorded.”

At the same time, some changes did appear in the climate records from both the high latitudes and the tropics. The researchers found that extreme drying in the tropics coincided with abrupt climate changes in the North Atlantic, at the tail end of glacial periods. It is thought that these rapid climate changes, known as Heinrich events, are triggered by large ice sheets suddenly plunging into the ocean.

“In the tropics, we see these events as very sharp periods of drying in the stalagmite record,” Adkins says. “We think that these droughts indicate that the tropics experienced a more El Niño-like climate at those times, causing them to dry out.” During El Niño events, warm waters from the tropics, near Borneo, shift toward the center of the Pacific Ocean, often delivering heavier rainfall than usual to the western United States while leaving Indonesia and its neighbors extremely dry and prone to forest fires.

The fact that the tropics responded to Heinrich events, but not to the shift that affected the high latitudes following the MBE, suggests that the climate system has two modes of responding to significant changes. “It makes you wonder if maybe the climate system cares about what sort of hammer you hit it with,” Adkins says. “If you nudge the system consistently over long timescales, the tropics seem to be able to continue independently of the high latitudes. But if you suddenly whack the climate system with a big hammer, the impact spreads out and shows up in the tropics.”

This work raises questions about the future in light of recent increases in atmospheric carbon dioxide: Is this increase more like a constant push? Or is it a whack with a big hammer? A case could be made for either one of these scenarios, says Adkins, but he adds that it would be easiest to argue that the forcing is more like a sudden whack, since the amount of carbon dioxide in the atmosphere has increased at such an unprecedented rate.

Mining for heat

Underground mining is a sweaty job, and not just because of the hard work it takes to haul ore: Mining tunnels fill with heat naturally emitted from the surrounding rock. A group of researchers from McGill University in Canada has taken a systematic look at how such heat might be put to use once mines are closed. They calculate that each kilometer of a typical deep underground mine could produce 150 kW of heat, enough to warm 5 to 10 Canadian households during off-peak times.

A number of communities in Canada and Europe already use geothermal energy from abandoned mines. Noting these successful, site-specific applications, the McGill research team strove to develop a general model that could be used by engineers to predict the geothermal energy potential of other underground mines. In a paper accepted for publication in the American Institute of Physics’ Journal of Renewable and Sustainable Energy, the researchers analyze the heat flow through mine tunnels flooded with water. In such situations, hot water from within the mine can be pumped to the surface, the heat extracted, and the cool water returned to the ground. For the system to be sustainable, heat must not be removed more quickly than it can be replenished by the surrounding rock. The team’s model can be used to analyze the thermal behavior of a mine under different heat extraction scenarios.

“Abandoned mines demand costly perpetual monitoring and remediating. Geothermal use of the mine will offset these costs and help the mining industry to become more sustainable,” says Seyed Ali Ghoreishi Madiseh, lead author on the paper. The team estimates that up to one million Canadians could benefit from mine geothermal energy, with an even greater potential benefit for more densely populated countries such as Great Britain.

Old maps and dead clams help solve coastal boulder mystery

This is the boulder ridge around the coastline of the Aran Islands. New research finds that storm waves have formed these ridges, despite the contention of some researchers that only a tsunami would have enough power to do this. -  Ronadh Cox
This is the boulder ridge around the coastline of the Aran Islands. New research finds that storm waves have formed these ridges, despite the contention of some researchers that only a tsunami would have enough power to do this. – Ronadh Cox

Perched atop the sheer coastal cliffs of Ireland’s Aran Islands, ridges of giant boulders have puzzled geologists for years. What forces could have torn these rocks from the cliff edges high above sea level and deposited them far inland?

While some researchers contend that only a tsunami could push these stones, new research in The Journal of Geology finds that plain old ocean waves, with the help of some strong storms, did the job.

And they’re still doing it.

The three tiny Aran Islands are just off the western coast of Ireland. The elongated rock ridges form a collar along extended stretches of the islands’ Atlantic coasts. The sizes of the boulders in the formations range “from merely impressive to mind-bogglingly stupendous,” writes Dr. Rónadh Cox, who led the research with her Williams College students. One block the team studied weighs an estimated 78 tons, yet was still cut free from its position 36 feet above sea level and shoved further inland.

Armed with equations that model the forces generated by waves, some researchers have concluded that no ordinary ocean waves could muster the force necessary to move the largest of the boulders this high above the ocean surface and so far inland. The math suggests the rocks in the ridges could only have been put there by a tsunami.

The equations tell one story. The islands’ residents tell another. According to some locals, enormous rocks have moved in their lifetimes, despite the fact that there hasn’t been a tsunami to hit the islands since 1755.

“Unless you have little green men from mars doing this on the quiet, it must be storm waves,” Cox said.

While the anecdotes from residents are interesting, Cox and her team went in search of more concrete evidence. The clincher came when the team compared modern high-altitude photos of the coastline to set of meticulous maps surveyed in 1839. The 19th century surveyors, who Cox describes as “possibly the most anal men on the planet,” carefully mapped not only the boulder ridges, but all of the criss-crossing stone walls that farmers built between fields. The researchers digitized the maps and overlaid them on the modern images, using the walls to line the two up accurately.

“Not only did they map every wall, they did it right. The maps aren’t even off by even a meter.”

The overlay of the new photos with the old maps shows definitively that sections of the ridges have moved substantially since

1839-nearly 100 years after the most recent tsunami. Some sections moved inland at an average rate of nearly 10 feet per decade. In some places, the ridge had run over and demolished field walls noted on the old maps.

Other lines of evidence corroborate residents’ accounts of recent movement. When the boulders were ripped from the bedrock, tiny clams that live in cracks and crevices sometimes came along for the ride. Using radiocarbon dating, Cox and her team found that some of the rocks have been pulled from the coastline within the last 60 years. What’s more, the researchers have been photographing sections of the ridge during each field season since 2006, and they’ve documented movement from year to year.

So what of the equations that point to tsunami as the only possible earth mover?

“We’ve eliminated tsunami and I think we can rule out little green men,” Cox said. “What that says is our equations aren’t good enough.”

Cox thinks the characteristics of the Aran Island shoreline are throwing off the calculations. The Aran cliffs rise nearly vertically out of the Atlantic, leaving very deep water close to the shore. As waves slam into the sheer cliff, that water is abruptly deflected back out toward the oncoming waves. This backflow may amplify subsequent waves. The result is an occasional storm wave that is much larger than one would expect.

“In this kind of environment these would be less rare,” Cox said. “You only need a couple of them to move these rocks around. The radiocarbon data show that not only are some boulders moving in recent years, but also that some of them have been in the ridges for hundreds and even a couple of thousand years. Accumulated activity of rare large-wave events over that time could certainly build these structures”

Cox plans to add a physicist to her research team in the near future to try to shed some light on the wave dynamics on the islands, but it’s clear from the evidence the team has already gathered that storm waves can do more than some researchers thought.

Following the devastating Indonesian tsunami in 2004, there has been renewed interest in learning about how a tsunami can change the landscape. Cox’s findings have important implications for that research.

“There’s a tendency to attribute the movement of large objects to tsunami,” she said. “We’re saying hold the phone. Big boulders are getting moved by storm waves.”

Arabic records allow past climate to be reconstructed

Baghdad became the most prosperous place at the time, and the center of international trade and agricultural development. -  Domínguez-Castro et al.
Baghdad became the most prosperous place at the time, and the center of international trade and agricultural development. – Domínguez-Castro et al.

Corals, trees and marine sediments, among others, are direct evidence of the climate of the past, but they are not the only indicators. A team led by Spanish scientists has interpreted records written in Iraq by Arabic historians for the first time and has made a chronology of climatic events from the year 816 to 1009, when cold waves and snow were normal.

The Arabic historians’ records chronologically narrate social, political and religious matters, and some of them mention climate. A study led by researchers from the University of Extremadura (Spain) has focused on ancient meteorological notes of the Iraqi city of Baghdad.

“We have recovered an interesting chronology of climatic events, such as droughts, floods, rain, frost, heat and cold waves as well as strong winds during the period between 816-1009 in the areas now known as Iraq and Syria” Fernando Domínguez-Castro, lead author and researcher in the Physics department at the University of Extremadura, informed SINC.

This study, which has been published in the Weather journal, highlights a high number of cold waves. “The period between 902 and 944 had a high number if we compare them to current weather data. Examples of this are the six snowfalls that occurred in that period, whilst in our era, we only know of one snowfall in Baghdad on 11 January 2008″ Domínguez-Castro highlights.

More cold days due to volcanic eruptions

The research team was especially surprised by the “unexpected” drop in temperatures in July 920. According to the documents analysed, the people of Baghdad had to come down from their roofs (where they would usually sleep in the summer) and go inside their houses and even use blankets. The temperatures could have dropped 9ºC compared to the current average for the month of July.

“It is difficult to identify the cause of this drop in temperature, but it could be due to a volcanic eruption the year before, as it is common for summer temperatures to drop in these cases” the expert points out and says that during some of those nights in July 920, temperatures did not exceed 18ºC.

There were two significant volcanic eruptions during that period, which could be the cause of the cold waves, “although there is a lot of doubt surrounding the dates”, the researcher states. One of those was the Ceboruco volcano (Mexico), around 930, and the other was the Guagua Pichincha (Ecuador), around 910. Nonetheless, “more evidence is necessary to confirm this hypothesis” the expert warns.

The research shows that during the first half of the tenth century, the cold climatic events in Baghdad were more frequent and more intense than today. Although in the Iraqi city only two days with temperatures below 0ºC were registered between 1954 and 2008, there were at least six very cold days in a 42 year period in the tenth century.

According to the researchers, “the Arabic records are very useful for reconstructing the climate in eras and places about which we know very little”. Thanks to the synergy of humans and science ‘robust climate information’ has been extracted” they conclude.

Baghdad, the center of the empire

In 762, Abu Ja’far Abdallah al-Mansur, the second Abbasid Caliph (the second Islamic dynasty), founded the city of Baghdad and established it as the capital of the empire. The city soon became the most prosperous place at the time, and the center of international trade and agricultural development, which attracted a growing population.

Historians of the era debated reasons as to why the Caliph gave so much importance to Baghdad. As well as its strategic location between the Tigris and Euphrates rivers, the city had good weather conditions. “There was plenty of water, the weather was very warm in the summer, very cold in the winter, and moderate in spring and autumn,” Al-Ya’qubi described, author of a geographical treatise in 891.

Yellowstone ‘super-eruption’ less super, more frequent than thought

The Yellowstone “super-volcano” is a little less super-but more active-than previously thought.

Researchers at Washington State University and the Scottish Universities Environmental Research Centre say the biggest Yellowstone eruption, which created the 2 million year old Huckleberry Ridge deposit, was actually two different eruptions at least 6,000 years apart.

Their results paint a new picture of a more active volcano than previously thought and can help recalibrate the likelihood of another big eruption in the future. Before the researchers split the one eruption into two, it was the fourth largest known to science.

“The Yellowstone volcano’s previous behavior is the best guide of what it will do in the future,” says Ben Ellis, co-author and post-doctoral researcher at Washington State University’s School of the Environment. “This research suggests explosive volcanism from Yellowstone is more frequent than previously thought.”

The new ages for each Huckleberry Ridge eruption reduce the volume of the first event to 2,200 cubic kilometers, roughly 12 percent less than previously thought. A second eruption of 290 cubic kilometers took place more than 6,000 years later.

That first eruption still deserves to be called “super,” as it is one of the largest known to have occurred on Earth and darkened the skies with ash from southern California to the Mississippi River. By comparison, the 1980 eruption of Mount St. Helens produced 1 cubic kilometer of ash. The larger blast of Oregon’s Mount Mazama 6,850 years ago produced 116 cubic kilometers of ash.

The study, funded by the National Science Foundation and published in the June issue of the Quaternary Geochronology, used high-precision argon isotope dating to make the new calculations. The radioactive decay rate from potassium 40 to argon 40 serves as a “rock clock” for dating samples and has a precision of .2 percent. Darren Mark, co-author and a post-doctoral research fellow at the SUERC, recently helped fine tune the technique and improve it by 1.2 percent-a small-sounding difference that can become huge across geologic time.

“Improved precision for greater temporal resolution is not just about adding another decimal place to a number, says Mark. “It’s far more exciting. It’s like getting a sharper lens on a camera. It allows us to see the world more clearly.”

The project asks the question: Might super-eruptions actually be products of multiple, closely spaced eruptions through time? With improved temporal resolution, in times to come, maybe super-eruptions will be not quite so super.