GeoLog

GeoLog

Imaggeo on Mondays: Hole in a hole in a hole…

Imaggeo on Mondays: Hole in a hole in a hole…

This photo, captured by drone about 80 metres above the ground, shows a nested sinkhole system in the Dead Sea. Such systems typically take form in karst areas, landscapes where soluble rock, such as limestone, dolomite or gypsum, are sculpted and perforated by dissolution and erosion. Over time, these deteriorating processes can cause the surface to crack and collapse.

The olive-green hued sinkhole, about 20 m in diameter, is made up of a mud material coated by a thin salted cover. When the structures collapse, they can form beautiful blocks and patterns; however, these sinkholes can form quite suddenly, often without any warning, and deal significant damage to roads and buildings. Sinkhole formations have been a growing problem in the region, especially within the last four decades, and scientists are working hard to better understand the phenomenon and the risks it poses to nearby communities and industries.

Some researchers are analysing aerial photos of Dead Sea sinkholes (taken by drones, balloons and satellites, for example) to get a better idea of how these depressions take shape.

“The images help to understand the process of sinkhole formation,” said Djamil Al-Halbouni, a PhD student at the GFZ German Research Centre for Geosciences in Potsdam, Germany and the photographer of this featured image. “Especially the photogrammetric method allows to derive topographic changes and possible early subsidence in this system.” Al-Halbouni was working at the sinkhole area of Ghor Al-Haditha in Jordan when he had the chance to snap this beautiful photo of one of the Dead Sea’s many sinkhole systems.

Recently, Al-Halbouni and his colleagues have employed a different kind of strategy to understand sinkhole formation: taking subsurface snapshots of Dead Sea sinkholes with the help of artificial seismic waves. The method, called shear wave reflection seismic imaging, involves generating seismic waves in sinkhole-prone regions; the waves then make their way through the sediments below. A seismic receiver is positioned to record the velocities of the waves, giving the researchers clues to what materials are present belowground and how they are structured. As one Eos article reporting on the study puts it, the records were essentially an “ultrasound of the buried material.”

The results of their study, recently published in EGU’s open access journal, Solid Earth, give insight into what kind of underground conditions are more likely to give way to sinkhole formation, allowing local communities to better pinpoint sites for future construction, and what spots are best left alone. This study and further work by Al-Halbouni and his colleagues have been published in a special issue organised by EGU journals: “Environmental changes and hazards in the Dead Sea region.”

By Olivia Trani, EGU Communications Officer

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Geosciences Column: How climate change put a damper on the Maya civilisation

Geosciences Column: How climate change put a damper on the Maya civilisation

More than 4,000 years ago, when the Great Pyramid of Giza and Stonehenge were being built, the Maya civilisation emerged in Central America. The indigenous group prospered for thousands of years until its fall in the 13th century (potentially due to severe drought). However, thousands of years before this collapse, severely soggy conditions lasting for many centuries likely inhibited the civilisation’s development, according to a recent study published in EGU’s open access journal Climate of the Past.

During their most productive era, often referred to as the Classic period (300-800 CE), Maya communities had established a complex civilisation, with a network of highly populated cities, large-scale infrastructure, a thriving agricultural system and an advanced understanding in mathematics and astronomy. However, in their early days, dating back to at least 2600 BCE, the Maya people were largely mobile hunter-gatherers, hunting, fishing and foraging across the lowlands.

Around 1000 BCE, some Maya communities had started to transition away from their nomadic lifestyles, and instead were moving towards establishing more sedentary societies, building small villages and relying more heavily on cultivating crops for their sustenance. However, experts suggest that agricultural practices didn’t gain momentum until 400 BCE, raising the question as to why Maya development was delayed for so many centuries.

By analysing two new palaeo-precipitation records, Kees Nooren, lead author of the study and a researcher at Utrecht University in the Netherlands, and his colleagues were able to gain insight into the environmental conditions during this pivotal time, and the impact that climate change could have had on the Maya society.

To determine the regional climate conditions during this period of time, the authors examined a beach ridge plain in the Mexican state of Tabasco, off the Gulf of Mexico, which contains a long-term record of ridge elevation changes for much of the late Holocene. Since precipitation has a large influence on the elevation of this beach ridge, this record is a good indicator of how much rainfall and flooding may have occurred during Maya settlement.

A large part of the central Maya lowlands (outlined with a black dashed line) is drained by the Usumacinta (Us.) River (a). During the Pre-Classic period this river was the main supplier of sand contributing to the formation of the extensive beach ridge plain at the Gulf of Mexico coast (b). Periods of low rainfall result in low river discharges and are associated with relatively elevated beach ridges. Taken from Nooren, K et al., 2018

Additionally, the researchers also assessed core samples taken from Lake Tuspan, a shallow body of water in northern Guatemala that is situated within the Central Maya Lowlands. Because the lake receives its water almost exclusively from a small section of the region (770 square kilometres), its sediment layers provide a good record of rainfall on a very local scale.

The image on p. 74 of the Dresden Codex depicts a torrential downpour probably associated with a destructive flood (Thompson, 1972). Taken from Nooren, K et al., 2018

The research team’s analysis suggested that, starting around 1000-850 BCE, the region shifted from a relatively dry climate, to a wetter environment. Such conditions would have made a farming in this region more difficult and less appealing compared to foraging and hunting. The researchers suggest that this change in climate could be one of the reasons why Maya agricultural development was at a standstill for such a long time.

The researchers also propose that this long-term climate trend could have been brought on by a shift of the Intertropical Convergence Zone (ITCZ), a region near the equator where northeast and southeast winds intermingle and where most of the Earth’s rain makes landfall. The position of this zone can move naturally in response to Earth’s changes in insolation, and a northerly shift of the ITCZ could help account for some of the morphological changes the authors observed in the precipitation records.

After more than 450 years of excessive rainfall and large floods, the records then suggest that the region experienced drier conditions once again. By this time period, the Maya populations began to rapidly intensify their farming efforts and develop major cities, further suggesting that the wet conditions may have helped delay such efforts.

This is not the first time the Nooren and his colleagues have found evidence of major environmental influence on the Maya civilisation. For example, earlier research led by Nooren suggests that, in the 6th century, the El Chichón volcano in southern Mexico released massive amounts of sulfur into the stratosphere, triggering global climate change that likely contributed to a ‘dark age’ in Maya history for several decades. During this time, often referred to as the “Maya Hiatus,’ Maya societies experienced stagnation, increased warfare and political unrest. The research results were presented at the 2016 General Assembly and later published in Geology.

The results of these studies highlight how changes in our climate have greatly influenced communities and at times even shaped the course of societal history, both for better and for worse.

By Olivia Trani, EGU Communications Officer

References

Ebert, C. et al.: Regional response to drought during the formation and decline of Preclassic Maya societies. Quaternary Science Reviews 173:211-235, 2017

Nooren, K., Hoek, W. Z., Dermody, B. J., Galop, D., Metcalfe, S., Islebe, G., and Middelkoop, H.: Climate impact on the development of Pre-Classic Maya civilization. Clim. Past, 14, 1253-1273, 2018

Nooren, K.: Holocene evolution of the Tabasco delta – Mexico : impact of climate, volcanism and humans. Utrecht University Repository (Dissertation). 2017

Nooren, K. et al.: Explosive eruption of El Chichón volcano (Mexico) disrupted 6th century Maya civilization and contributed to global cooling, Geology, 45, 175-178, 2016

Press conference: Volcanoes, climate changes and droughts: civilisational resilience and collapse. European Geosciences Union General Assembly 2016

Caltech Climate Dynamics Group, Why does the ITCZ shift and how? 2016

Join us at the EGU 2019 General Assembly: Call for abstracts is now open!

Join us at the EGU 2019 General Assembly: Call for abstracts is now open!

From now, up until 10 January 2019, you can submit your abstract for the upcoming EGU General Assembly (EGU 2019).

In addition to established scientists, PhD students and other early career researchers are welcome to submit abstracts to present their research at the conference. Further, the EGU encourages undergraduate and master students to submit abstracts on their dissertations or final-year projects.

The EGU recognises that there are many outstanding students who would benefit from attending and presenting at the General Assembly and, therefore, provides a discounted registration rate to this group. Interested undergraduates can apply to present a poster, talk or PICO presentation on research undertaken in a laboratory setting, on a mapping or field project they’ve been involved in during their degrees, or any other research project of relevance.

Browse through the EGU 2019 sessions. Clicking on ‘Please select’ will allow you to search for sessions by programme groups and submit your abstract to the relevant session either as plain text, LaTeX, or a MS Word document. Further guidelines on how to submit an abstract are available on the EGU 2019 website.

An innovative presentation format – Presenting Interactive Content, better known as PICO – has been implemented at the General Assembly since 2013. PICO sessions bring together the advantages of both oral and poster sessions, allowing authors to present the essence of their work and follow it up with interactive discussion. Please note that some sessions are ‘PICO only’ sessions, meaning you cannot select oral/poster preference. If you are submitting to a PICO only session be sure to check out our PICO guide, for tips on how to prepare your presentation.

The deadline for the receipt of abstracts is 10 January 2019, 13:00 CET. If you would like to apply for financial support, called the Roland Schlich travel support, to attend the 2019 General Assembly, please submit an application no later than 1 December 2018. We’ll be providing further information about how to apply for travel grants and how they are awarded in a forthcoming post.

EGU 2019 will take place from 7 to 12 April 2019 in Vienna, Austria. For more information on the General Assembly, see the EGU 2019 website and follow us on Twitter (#EGU19 is the official conference hashtag) and Facebook.

NB: We strongly recommend booking accommodation for the 2019 General Assembly as soon as possible. The Vienna City Marathon (40,000 participants) will take place on Sunday, resulting in many hotels being fully booked the night before.