The sea level has been rising and falling over the last 2,500 years

Rising and falling sea levels over relatively short periods do not indicate long-term trends. An assessment of hundreds and thousands of years shows that what seems an irregular phenomenon today is in fact nothing new,' explains Dr. Dorit Sivan, who supervised the research.
The Templar palace in Acre, seen here, is one of the sites where this study was carried out. -  Amir Yurman, Director of the Leon Recanati Institute for Maritime Studies Maritime Workshop at the University of Haifa;
Courtesy of the University of Haifa
Rising and falling sea levels over relatively short periods do not indicate long-term trends. An assessment of hundreds and thousands of years shows that what seems an irregular phenomenon today is in fact nothing new,’ explains Dr. Dorit Sivan, who supervised the research.
The Templar palace in Acre, seen here, is one of the sites where this study was carried out. – Amir Yurman, Director of the Leon Recanati Institute for Maritime Studies Maritime Workshop at the University of Haifa;
Courtesy of the University of Haifa

“Rising and falling sea levels over relatively short periods do not indicate long-term trends. An assessment of hundreds and thousands of years shows that what seems an irregular phenomenon today is in fact nothing new,” explains Dr. Dorit Sivan, who supervised the research.*

The sea level in Israel has been rising and falling over the past 2,500 years, with a one-meter difference between the highest and lowest levels, most of the time below the present-day level. This has been shown in a new study supervised by Dr. Dorit Sivan, Head of the Department of Maritime Civilizations at the University of Haifa. “Rises and falls in sea level over relatively short periods do not testify to a long-term trend. It is early yet to conclude from the short-term increases in sea level that this is a set course that will not take a change in direction,” explains Dr. Sivan.

The rising sea level is one of the phenomena that have most influence on humankind: the rising sea not only floods the littoral regions but also causes underground water salinization, flooded effluents, accelerated coastal destruction, and other damage.

According to Dr. Sivan, the changing sea level can be attributed to three main causes: the global cause – the volume of water in the ocean, which mirrors the mass of ice sheets and is related to global warming or cooling; the regional cause – vertical movement of the earth’s surface, which is usually related to the pressure placed on the surface by the ice; and the local cause – vertical tectonic activity. Seeing as Israel is not close to former ice caps and the tectonic activity along the Mediterranean coast is negligible over these periods, it can be concluded that drastic changes in Israel’s sea levels are mainly related to changes in the volume of water.

In the present study, in light of earlier studies, research student Ayelet Toker and Dr. Sivan, set out to examine Israel’s sea level over the past 2,500 years, based on data deduced from many coastal archaeological findings. They made a careful selection of findings that have been reliably and accurately dated, and first focused on findings that were excavated by the Antiquities Authority in Acre of the Crusader period. These revealed that the sea level during the Crusader period – just 800 years ago – was some 50-90 centimeters lower than the present sea level. Findings from the same period at Caesarea and Atlit reinforced this conclusion. When additional sites were examined from periods before and after the Crusader period, it was revealed that there have been significant fluctuations in sea level: During the Hellenistic period, the sea level was about 1.6 meters lower than its present level; during the Roman era the level was almost similar to today’s; the level began to drop again during the ancient Muslim period, and continued dropping to reach the same level as it was during the Crusader period; but within about 500 years it rose again, and reached some 25 centimeters lower than today’s level at the beginning of the 18th century.

“Over the past century, we have witnessed the sea level in Israel fluctuating with almost 19 centimeters between the highest and lowest levels. Over the past 50 years Israel’s mean sea level rise is 5.5 centimeters, but there have also been periods when it rose by 10 centimeters over 10 years. That said, even acute ups and downs over short periods do not testify to long-term trends. An observation of the sea levels over hundreds and thousands of years shows that what seems a phenomenon today is as a matter of fact “nothing new under the sun”, Dr. Sivan concludes.

Maximum height of extreme waves up dramatically in Pacific Northwest

Waves crawl up against the lower level of a structure in Neskowin, Oregon, during a storm in January, 2008. (Photo by Armand Thibault, Neskowin)
Waves crawl up against the lower level of a structure in Neskowin, Oregon, during a storm in January, 2008. (Photo by Armand Thibault, Neskowin)

A major increase in maximum ocean wave heights off the Pacific Northwest in recent decades has forced scientists to re-evaluate how high a “100-year event” might be, and the new findings raise special concerns for flooding, coastal erosion and structural damage.

The new assessment concludes that the highest waves may be as much as 46 feet, up from estimates of only 33 feet that were made as recently as 1996, and a 40 percent increase. December and January are the months such waves are most likely to occur, although summer waves are also significantly higher.

In a study just published online in the journal Coastal Engineering, scientists from Oregon State University and the Oregon Department of Geology and Mineral Industries report that the cause of these dramatically higher waves is not completely certain, but “likely due to Earth’s changing climate.”

Using more sophisticated techniques that account for the “non-stationarity” in the wave height record, researchers say the 100-year wave height could actually exceed 55 feet, with impacts that would dwarf those expected from sea level rise in coming decades. Increased coastal erosion, flooding, damage to ocean or coastal structures and changing shorelines are all possible, scientists say.

“The rates of erosion and frequency of coastal flooding have increased over the last couple of decades and will almost certainly increase in the future,” said Peter Ruggiero, an assistant professor in the OSU Department of Geosciences. “The Pacific Northwest has one of the strongest wave climates in the world, and the data clearly show that it’s getting even bigger.

“Possible causes might be changes in storm tracks, higher winds, more intense winter storms, or other factors,” Ruggiero said. “These probably are related to global warming, but could also be involved with periodic climate fluctuations such as the Pacific Decadal Oscillation, and our wave records are sufficiently short that we can’t be certain yet. But what is clear is the waves are getting larger.”

In the early 1990s, Ruggiero said, a fairly typical winter might have an offshore wave maximum of a little more than 25 feet. It was believed then – based primarily on data from two offshore buoys – that 10 meters, or 33 feet, would be about as large as waves would ever get, even in a massive “100-year” storm.

But then a major El Nino – which tends to bring larger waves, higher water levels and increased erosion – happened in 1997-98 and led to a string of “100-year” wave events of around and above 33 feet. Researchers went back to the drawing board, continued to study data and storm events, and now believe that the maximum waves the region may face could approach or even exceed 50 feet.

Increasing wave heights, they said, have had double or triple the impact in terms of erosion, flooding and damage as sea level rise over the last few decades. If wave heights continue to increase, they may continue to dominate over the acceleration in sea level that’s anticipated over the next couple of decades. The prior concern about what sea level rise could do, in other words, is already a reality. If sea levels do increase significantly in future decades and centuries, that will only add to the damage already being done by higher waves.

Exactly what impacts this will have in terms of beach erosion and shifting shorelines is difficult to predict, scientists say, because currents and sand move in complex ways, creating both “winners and losers” in terms of beach stability. But some effects are already visible, Ruggiero said.

“Neskowin is already having problems with high water levels and coastal erosion,” Ruggiero said. “Some commercial structures there occasionally lose the use of their lower levels.

“Going to the future, communities are going to have to plan for heavier wave impacts and erosion, and decide what amounts of risk they are willing to take, how coastal growth should be managed and what criteria to use for structures,” he said.

Hampering the research effort is the fact that two of the major buoys used for these studies, which are some distance off the Pacific Northwest coast and measure waves in deep water, were only installed in the 1970s. Even at that they provide two of the longest high-quality wave height records in the world. OSU researchers are studying historical records through climate data, old newspaper records and other information to try to recreate what wave heights and storm events were like going further back in time.

The largest wave height increases, scientists say, have occurred off the Washington coast and northern Oregon, with less increase in southern Oregon and nothing of significance south of central California. The study also noted that similar increases in wave heights have occurred in the North Atlantic Ocean, as well as the seasonal total power generated by hurricanes.

These issues do not consider the potential drop in land level that is expected to occur in this region with a subduction zone earthquake at some point in the future. Ruggiero noted that he did some research in Sumatra following the huge 2004 earthquake there – an area with geology very similar to that of the Pacific Northwest – and some of the shoreline had dropped from 1.5 to five feet. If and when that occurs, the impacts on shorelines could be enormous.

Congo receives help from space after volcano eruption

The loss of coherence observed by the Advanced Synthetic Aperture Radar (ASAR) instrument on ESA’s Envisat between images acquired on 8 January 2010 and on 7 December 2009 allowed the GORISK team to detect one of the paths of the lava flows following the eruption of Mount Nyamuragira on 2 January 2010 in the Democratic Republic of Congo. - Credits: RMCA-NMNH
The loss of coherence observed by the Advanced Synthetic Aperture Radar (ASAR) instrument on ESA’s Envisat between images acquired on 8 January 2010 and on 7 December 2009 allowed the GORISK team to detect one of the paths of the lava flows following the eruption of Mount Nyamuragira on 2 January 2010 in the Democratic Republic of Congo. – Credits: RMCA-NMNH

On 2 January, Mount Nyamulagira in the Democratic Republic of Congo erupted, spewing lava from its southern flank and raising concerns that the 100 000 people in the town of Sake could be under threat.

Fears were also triggered in Goma as rumours circulated that an eruption was imminent at the nearby Nyiragongo volcano, which devastated the city in 2002.
Following the eruption, scientists and local authorities have been using a long series of space images from ESA’s Envisat, together with seismic and helicopter data, to monitor the situation and calm fears of the local population.

Dr Nicolas d’Oreye of GORISK, which is in Congo assisting the Goma Volcano Observatory to collect and process satellite observations and field data, said the satellite images are very useful for managing the crisis.

“As well as helping to validate information from different datasets, the satellite images are providing invaluable information about the situation, such as the details about the lava flow and the fact that the Nyiragongo volcano is not showing any signs of abnormal activity.

“This has been of great importance for the local authorities and the Goma Volcano Observatory, who are holding daily crisis meetings, to reassure the local population and humanitarian agencies that Nyiragongo will be unaffected by the eruption of Nyamulagira.”

Goma, the capital of the North Kivu province, is situated along the southern margin of the lava fields from these volcanoes. Lava from the Nyamulagira (height 3058 m) eruption has been flowing in a direction south and southwest of the volcano, raising concerns that lava could cover the Goma and Sake road within weeks, causing widespread chaos and threatening the local economy.

“Lava flows from Nyamulagira are usually not a direct threat for the population and the infrastructure except when it develops southwards, as it is in this case,” explained Dr d’Oreye, a senior scientist at the Geophysics/Astrophysics Department of the National Museum of Natural History in Luxembourg. “In this situation, it is crucial to monitor the flow size, direction and speed for the authorities to be able to make timely decisions.”

Lava flows can be mapped by comparing satellite radar images acquired before and after the eruption. In the images, old lava appears bright white. If an area appears white in before images and black in after images, then the ground has changed between acquisitions by the flow of new lava.

By comparing images acquired over the area before and after the eruption by the Advanced Synthetic Aperture Radar (ASAR) on Envisat, the GORISK team was able to detect a lava flow in the main caldera and one of the paths of the flows.

Although scientists are not worried about the lava flow reaching Lake Kivu during this eruption, they continue to observe the situation. If lava were to flow into the lake, as has occurred several times in the recent past, there is a small chance that it might trigger the gas (mainly carbon dioxide and methane) in the lake to release quickly.

This mixture could create a flammable cloud with possible catastrophic consequences, as in 1986 when Lake Nyos in Cameroon released a cloud of gas that killed more than 1700 people. Scientists think lava flows that reach the lake after 20 km are not harmful for the lake itself.

To learn how the ground deformed during the volcanic eruption, the team used a technique called ‘SAR interferometry’, or InSAR, to construct an ‘interferogram’ image by analysing the differences between two radar signals taken over the same area on Earth at different times.

The first interferogram processed after the onset of the eruption, based on data from 7 December 2009 and 8 January 2010, shows the ground deformation due to the eruption. A complete set of coloured bands, called ‘fringes’, represents ground movement relative to the spacecraft of 2.8 cm in the case of Envisat’s ASAR.

The team has been systematically monitoring the area by InSAR since 2005 and continues to acquire about six new SAR scenes per month. The thousands of interferograms computed by the team so far have provided a detailed picture of the site and afforded experience in distinguishing real ground deformation from possible artefacts.

The InSAR technique was also applied to data over Mount Nyiragongo to determine whether there were any signs of activity at the volcano.

In order to evaluate the level of risk and increase their knowledge of volcanoes, volcanologists need continuous data over long periods. In some cases, only a satellite is capable of providing this, because some areas are inaccessible or too dangerous to be approached. For instance, to reach Mount Nyamulagira by ground scientists would have to travel through dense tropical forests in a region where rebel forces are present.

Envisat can supply this much-needed information and provide accurate maps of areas at risk. Continuously gathered satellite data can be used to assess risk and detect the slight signs of change that may foretell an eruption.

When an eruption begins, optical and radar instruments can image the various phenomena associated with it, including lava flows, mud slides, ground fissures and earthquakes. Atmospheric sensors can identify the gases and aerosols released by the eruption, and quantify their wider environmental impact.

The GORISK project, funded by the Belgian Science Policy Office and the National Research Fund of Luxembourg, aims to improve and implement techniques dedicated to studying and monitoring the Nyamilagira and Nyiragongo volcanoes through space- and ground-based observations.

SAR images are provided as part of ESA category-1 projects through which the team also ensures the systematic monitoring of other volcanic areas in Cape Verde, Cameroon and Tanzania.

“This eruption is a good exercise for a potential eruption of Nyiragongo, which is the major concern for the city of Goma and its 800 000 inhabitants,” Dr d’Oreye said.

San Andreas Fault study unearths new quake information

View of the 'Southeast' channel of the Bidart fan, Carrizo Plain, looking downstream. The channel is offset approximately 10 m by the San Andreas fault, at the bend in the middle ground of the photo, near the pump can. Trench 18, or 'T18' (foreground) was excavated to exposure sediment in the channel for mapping and radiocarbon dating. -  Bidart Fan San Andreas fault research team, University of California Irvine and Arizona State University
View of the ‘Southeast’ channel of the Bidart fan, Carrizo Plain, looking downstream. The channel is offset approximately 10 m by the San Andreas fault, at the bend in the middle ground of the photo, near the pump can. Trench 18, or ‘T18′ (foreground) was excavated to exposure sediment in the channel for mapping and radiocarbon dating. – Bidart Fan San Andreas fault research team, University of California Irvine and Arizona State University

Recent collaborative studies of stream channel offsets along the San Andreas Fault by researchers at Arizona State University and UC Irvine reveal new information about fault behavior – affecting how we understand the potential for damaging earthquakes.

The researchers’ findings encompasses their work at the Carrizo Plain, which is located 100 miles north of Los Angeles and site of the original “Big One” – the Fort Tejon quake of 1857. Applying a system science approach, the ASU-UCI team presents a pair of studies appearing Jan. 21 at Science Express that incorporates the most comprehensive analysis of this part of the San Andreas fault system to date.

In one of the studies, Ramon Arrowsmith, an associate professor in the School of Earth and Space Exploration in ASU’s College of Liberal Arts and Sciences, and Dr. Olaf Zielke employed topographic measurements from LiDAR (Light Detection and Ranging), which provide a view of the earth’s surface at a resolution at least 10 times higher than previously available, enabling the scientists to “see” and measure fault movement, or offset.

To study older earthquakes, researchers turn to offset landforms such as stream channels which cross the fault at a high angle. A once straight stream channel will have a sharp jog right along the fault and indicate that prior offset.

This highly detailed overhead view of Carrizo Plain stream channels measured the offset features linked to large earthquakes in this section of the southern San Andreas Fault.

“This virtual approach is not a substitute for going out and looking at the features on the ground,” says Zielke, who earned his Ph.D. at ASU under Arrowsmith. “But it is a powerful and somewhat objective approach that is also repeatable by other scientists.”

In the second Science Express study, a team led by UCI’s Lisa Grant Ludwig with postdoctoral scholar Sinan Akciz and Ph.D. candidate Gabriela Noriega determined the age of offset in a few Carrizo Plain dry stream channels by studying how much the fault slipped during previous earthquakes. The distance that a fault ‘slips’, or moves, determines its offset.


By digging trenches across the fault, radiocarbon-dating sediment samples and studying historic and older weather data of these Carrizo Plain channels, and combining them with the LiDAR data, the researchers found something other than what scientists had thought. Instead of having the same slip repeat in characteristic ways, researchers found that slip varied from earthquake to earthquake.

“When we combine our offset measurements with estimates of the ages of the offset features determined by Lisa’s team and the ages of prior earthquakes, we find that the earthquake offset from event to event in the Carrizo Plain is not constant, as is current thinking” Arrowsmith said.

“The idea of slips repeating in characteristic ways along the San Andreas Fault is very appealing, because if you can figure that out, you are on your way to forecasting earthquakes with some reasonable confidence,” added Ludwig, an associate professor of public health. “But our results show that we don’t understand the San Andreas Fault as well as we thought we did, and therefore we don’t know the chances of earthquakes as well as we thought we knew them.”

Before these studies, the M 7.8 Fort Tejon earthquake of 1857 (the most recent earthquake along the southern San Andreas Fault) was thought to have caused a 9 to 10 meter slip along the Carrizo Plain. But the data the teams acquired show that it was actually half as much, and that slip in some of the prior earthquakes may have been even less. The researchers also found that none of the past five large earthquakes in the Carrizo Plain dating back 500 years produced slip anywhere near nine meters. In fact, the maximum slip seen was about 5-6 meters, which includes the slip caused by the Fort Tejon quake.

This result changes how we think the San Andreas Fault behaves: it probably is not as segmented in its release of accumulated stress. This makes forecasting future earthquakes a bit harder because we cannot rely on the assumption of constant behavior for each section. It could mean that earthquakes are more common along the San Andreas, but some of those events are probably smaller than we had previously expected.

Since the 1857 quake, an approximate five meters of strain, or potential slip, has been building up on the San Andreas Fault in the Carrizo Plain, ready to be released in a future earthquake. In the last five earthquakes, the most slip that has been released was 5-6 meters in the big 1857 quake. This finding points to the potential of a large temblor along the southern San Andreas Fault.

“Our collaboration has produced important information about how the San Andreas Fault works. Like all science, it is pushed forward by hard work, good ideas, and new technology. I am optimistic that these results, which change how we think about how faults work, are moving us to a more subtle understanding of the complexity of the earthquake process,” said Arrowsmith.

“The recent earthquake in Haiti is a reminder that a destructive earthquake can strike without warning. One thing that hasn’t changed is the importance of preparedness and earthquake resistant infrastructure in seismically active areas around the globe,” Ludwig added.

Cave reveals Southwest’s abrupt climate swings during Ice Age

Sarah Truebe, a geosciences doctoral student at the University of Arizona, checks on an experiment that measures how fast cave formations grow in Arizona's Cave of the Bells. -  Copyright 2010 Stella Cousins.
Sarah Truebe, a geosciences doctoral student at the University of Arizona, checks on an experiment that measures how fast cave formations grow in Arizona’s Cave of the Bells. – Copyright 2010 Stella Cousins.

Ice Age climate records from an Arizona stalagmite link the Southwest’s winter precipitation to temperatures in the North Atlantic, according to new research.

The finding is the first to document that the abrupt changes in Ice Age climate known from Greenland also occurred in the southwestern U.S., said co-author Julia E. Cole of the University of Arizona in Tucson.

“It’s a new picture of the climate in the Southwest during the last Ice Age,” said Cole, a UA professor of geosciences. “When it was cold in Greenland, it was wet here, and when it was warm in Greenland, it was dry here.”

The researchers tapped into the natural climate archives recorded in a stalagmite from a limestone cave in southern Arizona. Stalagmites grow up from cave floors.

The stalagmite yielded an almost continuous, century-by-century climate record spanning 55,000 to 11,000 years ago. During that time ice sheets covered much of North America, and the Southwest was cooler and wetter than it is now.

Cole and her colleagues found the Southwest flip-flopped between wet and dry periods during the period studied.

Each climate regime lasted from a few hundred years to more than one thousand years, she said. In many cases, the transition from wet to dry or vice versa took less than 200 years.

“These changes are part of a global pattern of abrupt changes that were first documented in Greenland ice cores,” she said. “No one had documented those changes in the Southwest before.”

Scientists suggest that changes in the northern Atlantic Ocean’s circulation drove the changes in Greenland’s Ice Age climate, Cole said. “Those changes resulted in atmospheric changes that pushed around the Southwest’s climate.”

She added that observations from the 20th and 21st centuries link modern-day alterations in the North Atlantic’s temperature with changes in the storm track that controls the Southwest’s winter precipitation.

“Also, changes in the storm track are the kinds of changes we expect to see in a warming world,” she said. “When you warm the North Atlantic, you move the storm track north.”

The team’s paper, “Moisture Variability in the Southwestern U.S. Linked to Abrupt Glacial Climate Change,” is scheduled for publication in the February issue of Nature Geoscience. Cole’s UA co-authors are Jennifer D. M. Wagner, J. Warren Beck, P. Jonathan Patchett and Heidi R. Barnett. Co-author Gideon M. Henderson is from the University of Oxford, U.K.

Cole became interested in studying cave formations as natural climate archives about 10 years ago. At the suggestion of some local cave specialists, she and her students began working in the Cave of the Bells, an active limestone cave in the Santa Rita Mountains.

In such a cave, mineral-rich water percolates through the soil into the cave below and onto its floor. As the water loses carbon dioxide, the mineral known as calcium carbonate is left behind. As the calcium carbonate accumulates in the same spot on the cave floor over thousands of years, it forms a stalagmite.

The researchers chose the particular stalagmite for study because it was deep enough in the cave that the humidity was always high, an important condition for preservation of climate records, Cole said. Following established cave conservation protocols, the researchers removed the formation, which was less than 18 inches tall.

For laboratory analyses, first author Wagner took a core about one inch in diameter from the center of the stalagmite. The scientists then returned the formation to the cave, glued it back into its previous location with special epoxy and capped it with a limestone plug.

To read the climate record preserved in the stalagmite, Wagner sliced the core lengthwise several times for several different analyses.

On one slice, she shaved more than 1,200 hair-thin, 100-micron samples and measured what types of oxygen molecule each one contained.

A rare form of oxygen, oxygen-18, is more common in the calcium carbonate deposited during dry years. By seeing how much oxygen-18 was present in each layer, the scientists could reconstruct the region’s pattern of wet and dry climate.

To assign dates to each wet and dry period, Wagner used another slice of the core for an analysis called uranium-thorium dating.

The radioactive element uranium is present in minute amounts in the water dripping onto a stalagmite. The uranium then becomes part of the formation. Uranium decays into the element thorium at a steady and known rate, so its decay rate can be used to construct a timeline of a stalagmite’s growth.

By matching the stalagmite’s growth timeline with the sequence of wet and dry periods revealed by the oxygen analyses, the researchers could tell in century-by-century detail when the Southwest was wet and when it was dry.

“This work shows the promise of caves to providing climate records for the Southwest. It’s a new kind of climate record for this region,” Cole said.

She and her colleagues are now expanding their efforts by sampling other cave formations in the region.

Volcanic hazard map produced for island of Gran Canaria

This is the volcanic hazard map for the island of Gran Canaria. -  Rodríguez-González et al.
This is the volcanic hazard map for the island of Gran Canaria. – Rodríguez-González et al.

Spanish and French researchers have defined the age, location, size and geochemistry of the volcanoes of Gran Canaria during the Holocene, 11,000 years ago, in order to draw up a map of volcanic hazards for the island. The research shows that the area of greatest volcanic activity is one of the most heavily populated areas in the north east of the island, which has suffered 24 eruptions over the period studied.

The team of French and Spanish scientists led by researchers from the University of Las Palmas de Gran Canaria (ULPGC) and the “Jaume Almera” Institute of Earth Sciences (CSIC, Barcelona) combined the data from previous studies with the results of analysis of 13 new radiocarbon ages in order to gain an understanding of the history of the island and predict the areas to be struck by future volcanic eruptions.

The result, which has been published recently in the Journal of Quaternary Science, is a map of volcanic hazards for Gran Canaria, describing risk scenarios. “We have identified 24 volcanic eruptions that took place over the past 11,000 years on Gran Canaria. We know that volcanism was concentrated in the northern sector of the island and produced small monogenetic strombolian cones (eruptions that are not very violent and which release lava and pyroclastic flows) and, occasionally, phreatomagmatic calderas (which release ash), Alejandro Rodríguez-González, lead author of the study and a researcher at the ULPGC, tells SINC.

In order to create the map, the researchers based themselves on detailed field work, which enabled them to define the limits of the various volcanic units (cone, lava and horizontal spread of pyroclastic flows) with a great degree of exactitude, using geomorphologiccal and stratigraphic criteria.

The data now made available by the scientists makes it possible to better evaluate the scale and type of future eruptions in this area. By working out the areas, before and after, of each eruption using Digital Land Models (DLM), the researchers have developed a novel and very detailed morphometric methodology for this kind of volcanic environment.

The study started with palaeotopographical reconstructions of areas affected by recent volcanic activity. “This allows our methodology to show geomorphological changes according to volcanic type and the periods of erosion involved”, explains Rodríguez-González.

North of the island faces greatest risk of eruption

The volcanologists expect that the next volcanic eruption on the island will be of the “strombolian monogenetic type”, producing a cone of between 30 and 250 metres in height and a lava flow of between 100 and 10,000 metres in length.

One of the most heavily populated areas in the north east of the island has experienced the highest level of volcanic activity over the past 11,000 years, and it is therefore likely that this volcanic activity will continue in future. However, it is impossible to predict when such an eruption will take place. “While it is possible to determine where there is the greatest future danger, our current understanding of volcanic phenomena does not allow us to predict when an eruption will take place”, explains Rodríguez-González.

The new results highlight the fact that there were three groups of volcanic activity during the Holocene “separated by four periods of inactivity”. The first of these took place more than 10,000 years ago, with the single eruption at El Draguillo, to the east of the island. The other series of eruptions took place between 5,700 and 6,000 years ago, and between 1,900 and 3,200 years ago. Archaeological studies show that the most recent period of eruptions affected prehistoric human settlements on the island.

However, the researchers say that currently “the number of eruptive centres is on the increase, and periods of volcanic inactivity are getting shorter”. They also warn that over the past 11,000 years “the amount of magma released has increased, as has the explosivity of eruptions”.

The seismic gap south of Istanbul




Geoscientists expect an earthquake along the North Anatolian Fault
Geoscientists expect an earthquake along the North Anatolian Fault

The chain of earthquakes along the North Anatolian fault shows a gap south of Istanbul. The expected earthquakes in this region represent an extreme danger for the Turkish megacity. A new computer study now shows that the tensions in this part of the fault zone could trigger several earthquakes instead of one individual large quake event. In the latest issue of Nature Geosciences (Vol 3, doi:10.1038/NGEO739) Tobias Hergert of the Karlsruhe Institute for Technology and Oliver Heidbach of the GFZ German Research Centre for Geosciences present the results of the computer simulation, which was developed within the framework of the CEDIM (Centre for Disaster Management and Risk Reduction Technology).project “Megacity Istanbul”.

The Izmit-Earthquake of August 1999 resulted in 18,000 death victims and was, with a magnitude of 7.4, the most recent quake of a series, which began in 1939 to the east of Turkey and gradually ran along the plate border between the Anatolian and the Eurasian Plate from east to west. Therefore, the next quake in this series is expected to take place west of Izmit, i.e. south of Istanbul. The city has, thus, a threatening earthquake risk.

An important factor in judging seismic hazard is the movement rates of the tectonic fault. For their study Hergert and Heidbach divided the area into 640,000 elements, in order to determine, three-dimensionally, the kinetics of the fault system. “The model results show that the movement rates at the main fault are between 10 and 45% smaller than accepted to-date” explains Oliver Heidbach of the GFZ. “In addition the movement rates vary by 40% along the main fault” The authors interpret this variability as an indication that the built-up tension in the Earth’s crust can also unload in two or three earthquakes with a smaller magnitude rather than in one enormous quake. This, however, by no means implies an all-clear for Istanbul. The authors explicitly point out in their article that the short distance of the main fault to Istanbul still represents an extreme earthquake risk for the megacity. The fault zone is less than 20 kilometres from the city boundary, disaster precaution before the occurrence of a quake is essential.

Jurassic ‘burn-down’ events and organic matter richness in the Kimmeridge Clay Formation

Monika Kodrans-Nsiah inspects an exposed section of the Kimmeridge Clay Formation on Dorset's 'Jurassic Coast.' -  Ian Harding (NOCS)
Monika Kodrans-Nsiah inspects an exposed section of the Kimmeridge Clay Formation on Dorset’s ‘Jurassic Coast.’ – Ian Harding (NOCS)

The sediments of the Kimmeridge Clay Formation were deposited during the Late Jurassic between around 160 and 145 million years ago, the age of the reptiles. They are the main oil source rock in the North Sea. However, within this unit beds rich in organic matter are interspersed with organic-poor sediments. New evidence demonstrates that organic-poor sediments were probably caused by post-depositional loss of organic matter during so-called ‘burn-down’ events.

The Kimmeridge Clay Formation is named after the English village of Kimmeridge on Dorset’s ‘Jurassic Coast’, a favorite haunt of fossil hunters. The sediments comprising the formation, which is particularly well exposed here, were probably deposited in shallow marine environment with an average water depth of 50-100 metres.

“We were particularly interested in the transition between organic-rich and organic-poor sediments,” said Dr Ian Harding of the University of Southampton’s School of Ocean and Earth Science at the National Oceanography Centre, Southampton (NOCS), and a member of the team that investigated the underlying processes.

A long-held hypothesis is that the organic-rich beds were the result of elevated planktonic productivity in sunlit surface waters, possibly accentuated by enhanced preservation of the resulting organic matter by the oxygen-depleted bottom waters resulting from this excess productivity.

A second possibility was that a cyclic rise and fall of the interface between oxygenated and oxygen-depleted waters was responsible for the transition between organic-rich and organic poor sediments. According to this theory, when oxygenated waters reached the seabed, organic matter already deposited would have been oxidised and degraded. These post-depositional ‘burn down’ events could have alternated with periods during which the bottom waters had little oxygen, favouring preservation of organic matter.

“The first theory emphasizes changes in the amount of organic matter reaching the seabed, while the ‘burn-down’ theory puts more weight on the relative dominance of preservation or degradation after it has got there,” said Dr Harding.

To distinguish between these two theories, he and colleagues from the University of Bremen and the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, analysed the chemical composition and organic content of a sediment core from a borehole in Swanworth Quarry in Dorset, originally drilled as part of the Natural Environment Research Council (NERC) Rapid Global Geological Events Project run by NOCS’ Prof. John Marshall.

Monika Kodrans-Nsiah, a PhD student jointly supervised by Dr Harding and Dr Karin Zonneveld (Bremen) was responsible for analyzing the fossilized organic cysts of various species of dinoflagellate, a group of tiny aquatic organisms, found in the sediments. Different dinoflagellate species are known to be adapted to different environmental conditions, so studying the distribution of ‘dinocyst’ fossils helps reconstruct past environments.

The lower part of the core was rich in organic carbon, with abundant dinocysts, and its chemical composition was indicative of anoxic conditions, implying that sediments were deposited and preserved in an oxygen-deficient environment.

However, the chemical composition of the uppermost sediments indicated the presence of oxygenated water when they were deposited. This transition was sudden, occurring at a drilling depth of 122.37 metres, but changes in organic content and dinocyst distributions were more gradual.

“It looks likely that influxes of well-oxygenated bottom water caused the oxidation and degradation of organic matter and cysts after they were deposited,” said Dr Harding: “This would explain the gradual reduction in the amount of organic matter above the transition, and provide support for the idea of ‘burn-down’ events during the Jurassic.”

New satellite maps of Haiti coming in

This is a damage evaluation map based on satellite data over the Port-au-Prince area of Haiti, following a 7.0 magnitude earthquake and several aftershocks that hit the Caribbean nation on 12 January. Map based on data from CNES's SPOT-5, JAXA's ALOS and the US-based GeoEye-1 satellites; this was processed by SERTIT. -  CNES, JAXA, GeoEye, SERTIT
This is a damage evaluation map based on satellite data over the Port-au-Prince area of Haiti, following a 7.0 magnitude earthquake and several aftershocks that hit the Caribbean nation on 12 January. Map based on data from CNES’s SPOT-5, JAXA’s ALOS and the US-based GeoEye-1 satellites; this was processed by SERTIT. – CNES, JAXA, GeoEye, SERTIT

As rescue workers scramble to provide assistance to hundreds of thousands of people following Haiti’s earthquake, Earth observation satellite data continues to provide updated views of the situation on the ground.

Following the 7.0-magnitude earthquake that hit Haiti on 12 January, international agencies requested satellite data of the area from the International Charter on ‘Space and Major Disasters’.

The Charter, an international initiative aimed at providing satellite data free of charge to those affected by disasters anywhere in the world, immediately began re-tasking their satellites to get the data urgently needed.

Data are being collected by various satellites including Japan’s ALOS, CNES’s Spot-5, the U.S.’s WorldView and QuickBird, Canada’s RADARSAT-2, China’s HJ-1-A/B and ESA’s ERS-2 and Envisat.

These data are being processed into maps that show the degree of destruction. As soon as new data arrives, updated maps will be produced and made available to the international community.

Haiti quake occurred in complex, active seismic region




The Haiti earthquake epicenter is marked by the star along the displaced portion (shown in red) of the Enriquillo-Plantain Garden Fault. The 7.0 magnitude quake struck along about one-tenth of the 500-km-long strike-slip fault. The region sits on a complex  seismic area made up of numerous faults and plates. The fault lines with small arrows denote a different kind of fault called thrust faults, where one plate dives under another. Strike-slip faults grind past one another. The dotted lines at bottom denote complex seafloor formations. (Source: Jansma, P. and Mattioli, G., 2005, GPS results from Puerto Rico and the Virgin Islands: constraints on tectonic setting and rates of active faulting, Geol. Soc. Amer. Spec. Paper 385 (ed. Paul Mann), 13-30.)
The Haiti earthquake epicenter is marked by the star along the displaced portion (shown in red) of the Enriquillo-Plantain Garden Fault. The 7.0 magnitude quake struck along about one-tenth of the 500-km-long strike-slip fault. The region sits on a complex seismic area made up of numerous faults and plates. The fault lines with small arrows denote a different kind of fault called thrust faults, where one plate dives under another. Strike-slip faults grind past one another. The dotted lines at bottom denote complex seafloor formations. (Source: Jansma, P. and Mattioli, G., 2005, GPS results from Puerto Rico and the Virgin Islands: constraints on tectonic setting and rates of active faulting, Geol. Soc. Amer. Spec. Paper 385 (ed. Paul Mann), 13-30.)

The magnitude 7.0 earthquake that triggered disastrous destruction and mounting death tolls in Haiti this week occurred in a highly complex tangle of tectonic faults near the intersection of the Caribbean and North American crustal plates, according to a quake expert at the Woods Hole Oceanographic Institution (WHOI) who has studied faults in the region and throughout the world.

Jian Lin, a WHOI senior scientist in geology and geophysics, said that even though the quake was “large but not huge,” there were three factors that made it particularly devastating: First, it was centered just 10 miles southwest of the capital city, Port au Prince; second, the quake was shallow-only about 10-15 kilometers below the land’s surface; third, and more importantly, many homes and buildings in the economically poor country were not built to withstand such a force and collapsed or crumbled.

All of these circumstances made the Jan. 12 earthquake a “worst-case scenario,” Lin said. Preliminary estimates of the death toll ranged from thousands to hundreds of thousands. “It should be a wake-up call for the entire Caribbean,” Lin said.

The quake struck on a 50-60-km stretch of the more than 500-km-long Enriquillo-Plantain Garden Fault, which runs generally east-west through Haiti, to the Dominican Republic to the east and Jamaica to the west.

It is a “strike-slip” fault, according to the U.S. Geological Survey, meaning the plates on either side of the fault line were sliding in opposite directions. In this case, the Caribbean Plate south of the fault line was sliding east and the smaller Gonvave Platelet north of the fault was sliding west.

But most of the time, the earth’s plates do not slide smoothly past one another. They stick in one spot for perhaps years or hundreds of years, until enough pressure builds along the fault and the landmasses suddenly jerk forward to relieve the pressure, releasing massive amounts of energy throughout the surrounding area. A similar, more familiar, scenario exists along California’s San Andreas Fault.

Such seismic areas “accumulate stresses all the time,” says Lin, who has extensively studied a nearby, major fault , the Septentrional Fault, which runs east-west at the northern side of the Hispaniola island that makes up Haiti and Dominican Republic. In 1946, an 8.1 magnitude quake, more than 30 times more powerful than this week’s quake, struck near the northeastern corner of the Hispaniola.

Compounding the problem, he says, is that in addition to the Caribbean and North American plates, , a wide zone between the two plates is made up of a patchwork of smaller “block” plates, or “platelets”-such as the Gonvave Platelet-that make it difficult to assess the forces in the region and how they interact with one another. “If you live in adjacent areas, such as the Dominican Republic, Jamaica and Puerto Rico, you are surrounded by faults.”

Residents of such areas, Lin says, should focus on ways to save their lives and the lives of their families in the event of an earthquake. “The answer lies in basic earthquake education,” he says.

Those who can afford it should strengthen the construction and stability of their houses and buildings, he says. But in a place like Haiti, where even the Presidential Palace suffered severe damage, there may be more realistic solutions.

Some residents of earthquake zones know that after the quake’s faster, but smaller, primary, or “p” wave hits, there is usually a few-second-to-one-minute wait until a larger, more powerful surface, or “s” wave strikes, Lin says. P waves come first but have smaller amplitudes and are less destructive; S waves, though slower, are larger in amplitude and, hence, more destructive.

“At least make sure you build a strong table somewhere in your house and school,” said Lin. When a quake comes, “duck quickly under that table.”

Lin said the Haiti quake did not trigger an extreme ocean wave such as a tsunami, partly because it was large but not huge and was centered under land rather than the sea.

The geologist says that aftershocks, some of them significant, can be expected in the coming days, weeks, months, years, “even tens of years.” But now that the stress has been relieved along that 50-60-km portion of the Enriquillo-Plantain Garden Fault, Lin says this particular fault patch should not experience another quake of equal or greater magnitude for perhaps 100 years.

However, the other nine-tenths of that fault and the myriad networks of faults throughout the Caribbean are, definitely, “active.”

“A lot of people,” Lin says, “forget [earthquakes] quickly and do not take the words of geologists seriously. But if your house is close to an active fault, it is best that you do not forget where you live.”