GeoLog

caves

Imaggeo on Mondays: The ephemeral salt crystals

Imaggeo on Mondays: The ephemeral salt crystals

Rock salt stalactites (Speleothems) are the indicators of entrance in a salt cave. These crystal stalactites precipitate from brine only at the entrance in the salt caves, as that is the only place where the physical and chemical properties of the air and the brine dripping from the ceiling allow these crystals to grow and be preserved. And they are extremely fragile – if there is just a small change in the brine’s chemistry or the air’s moisture, the crystals will vanish away, dissolved in a pool of brine or a stream of salt water flowing out of the cave. These stalactites of salt crystals are what we call secondary salt; that means the original salt (formed million years ago) dissolved in water and re-precipitated recently.

Yes, you heard right, the sediments that contain these caves are made of rock-salt in the ground. Actually, caves can be formed in various types of soluble materials, from limestone and gypsum to halite (rock salt) or even ice. The salt caves denote the presence of salt near the surface of the earth.

How does the salt get there? Well we do know that there have been moments in the history of the Earth when certain seas (salt giants) have accumulated enormous deposits of salt instead of the more familiar mud sediments. However, we still don’t completely understand the process. That is also due to the fact that, unlike other rocks, salt has a plastic behavior, it tends to ‘flow’ upwards through other rocks, towards the surface (pretty much like wet sand between your feet when at seaside). As salt squeezes its way up, it deforms the rocks around it and creates salt domes that are later dissolved by water. This dynamic behavior of salt means that there are very few places where we can find salt in its original location and the understanding of the natural mechanisms that form salt remains incomplete.

Earth scientists like me, try to understand the mechanism of salt formation. Because the big picture of the past environments where salt is formed is currently blurred, we try to recreate a ‘movie’ of the past, that starts long before the formation of salts and ends long after. In this ‘movie’ we look at the past geography (paleogeography) and past environment (paleoenvironmental) changes from before to after the formation of the salts in order to single out key patterns that can bring us closer to removing the blur from this interesting episode in the story of oceans and seas.

I took this photo while doing field work in eastern Romania. The photo was taken on a tributary of the ‘Slănicul de Buzău’ river in the Buzău Land Geopark, an area of outstanding geological beauty, in the outer hills of South-East Carpathians. When I was stumbling on the salt caves in the field, I had to put mapping and sample collecting on pause. The layers of rock I was following had disappeared, replaced by a chaotic pile of mud, salt and small rock fragments. All I could do was check these rock fragments scattered in the landscape, try to figure out from where they come from, what layers of rock  the salt destroyed and of course, enjoy the geometric beauty of the ephemeral crystals.

By Dan V. Palcu, postdoctoral researcher at the University of São Paulo, Brazil

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/.

Imaggeo on Mondays: Our QUEST for innovative tools to understand changing environments and climates

Imaggeo on Mondays: Our QUEST for innovative tools to understand changing environments and climates

The photo shown here shows typical sampling work underground. You can see Ola Kwiecien and Cinthya Nava Fernandez, researchers at Ruhr University Bochum in Germany, collecting dripwater in New Zealand’s Waipuna Cave as part of a four-year EU-funded monitoring programme. Our research aims at developing innovative geochemical indicators that we can use to quantify changes in the hydrological system or biosphere above the cave that result from variations in weather patterns and climate.

Caves are fantastic natural archives and laboratories. One can imagine caves like libraries of natural history: they host carbonate formations (such as stalagmites, stalactites, flowstones etc., collectively known as speleothems) which, like books, can be read by geochemists to learn about past climatic and environmental conditions. Importantly, these ‘stone books’ must, on the one hand, be protected from destruction by weathering, and on the other, must be written in a language that we can decipher. The secluded cave environment greatly helps protect speleothems from erosion and weathering, while monitoring the cave environment and hydrology allows us to learn the alphabet which nature uses to write natural history into the speleothems. Only then can we reconstruct, and ideally quantify, past environmental conditions.

Of special importance for our work in New Zealand is the El Nino-Southern Oscillation and the southern Westerlies. These two atmospheric subsystems strongly influence weather and climate in New Zealand. Southward or northward shifts of the Westerlies influence New Zealand crop yields and tourism, as well as the fishing economy, among others. El Nino and La Nina have equally strong impacts on weather patterns in New Zealand (and, in fact globally).

Despite many years of research, the mechanisms that cause changes to the ENSO and the Westerlies, and their interaction, still remain poorly understood. This lack of knowledge limits scientists’ efforts to estimate the magnitude and direction of changes that might result from ongoing global warming.

Our team of German, British and New Zealand geochemists, mathematicians, palaeoclimatologists and modellers set out to develop innovative tools and methods that would allow researchers to quantify, for example, changes in rainfall or seasonality, with the ultimate goal that these should be applicable globally. The manual sampling depicted in the photo might soon be replaced by an automatic sampler, which would greatly reduce the costs for regular fieldwork. Especially in remote settings such robots would be of great benefit for our research.

Our team also developed new proxies, such as a lignin-based (biomarker) proxy that allows us to reconstruct changes in vegetation above the cave. We also explored how transition metals behave in the hydrological system of caves, and the factors that control how these metals are transported and incorporated into speleothems. These research activities will hopefully give us powerful and very sensitive tools to quantify changes of environmental parameters, including rainfall, temperature, soil and vegetation and the underlying forcings, like ENSO. Until we have our tool kit properly calibrated, we continue our visits to Waipuna and other caves in New Zealand and Germany.

Our QUEST project has received funding from the European Union’s Horizon 2020 Research and Innovation programme and the Royal Society of New Zealand. Find more at http://quest.pik-potsdam.de/

By Sebastian Breitenbach, Ruhr University Bochum (Germany), and Adam Hartland, University of Waikato (New Zealand)

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/.

Imaggeo on Mondays: Exploring the underground cryosphere

Imaggeo on Mondays: Exploring the underground cryosphere

The winter season is a good time to take advantage of cold weather activities, whether that’s hitting the ski slopes or warming up by a fire, but for Renato R. Colucci, it’s also one of the best time’s to study the Earth’s underground cryosphere.

Colucci, who took this featured photograph, is a researcher at Italian Institute for Marine Sciences (ISMAR) of the National Research Council (CNR) and is a scientific lead partner for the Cave’s Cryosphere and Climate project, C3 for short. The C3 project aims to monitor, study, date, and model alpine ice cave environments.

This photo was taken by Colucci while he and the C3 project team were surveying a large ice deposit in the Vasto cave, situated within the Southeastern Alps of Italy. Speleologists of the E. Boegan Cave Commission began documenting the caves in this region in the 1960s, making it a great site for studying underground cryosphere today. For the past few years the C3 team has been monitoring the microclimates of these caves as well as analysing how the ice masses within are melting and accumulating ice.

There are many different kinds of ice deposits in caves, but the main difference is how these types accumulate their frozen mass. For some cave ice deposits, like the one featured in this photo, the snowfall that reaches the cave interior amasses over time into solid layers of ice, as is typical for many glaciers. However, other deposits take form when water from melting snow or rain percolates through rock’s voids and fractures, then freezes and accumulates into permanent ice bodies in caves.

These high-altitude underground sources of ice are a lesser-known faction of the cryosphere since they are not very common or reachable to scientists, but still an important one. Often the permanent ice deposits in caves contain pivotal information on how Earth’s climate has evolved over time during the Holocene.

However, if the Earth’s global temperatures keep increasing, this data might not be available in the future. While ice masses in caves are more resilient to climate change compared to their aboveground counterparts, many of these deposits, and the vital data they store, are melting away at an accelerating rate. “Global warming is rapidly destroying such important archives,” said Colucci.

Through this project, the researchers involved hope to better understand the palaeoclimate information stored in these deposits and how the ice will respond to future climate change.

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/.

Imaggeo on Mondays: A volcanic point of view

Imaggeo on Mondays: A volcanic point of view

It’s not every day that you can peer into a volcano, much less gaze out at the sky from the inside of one. The Algar do Carvão, or “the Cavern of Coal,” is one of the few places on Earth where you can explore the underground reaches of a volcanic site.

The volcanic pit is found on the island of Terceira, part of the Azores archipelago. This collection of islands is an autonomous region of Portugal, located in the Atlantic Ocean about 1800 kilometres west from the Portuguese mainland. The archipelago is an especially volcanic hotspot, situated on the border of three major tectonic plates: the North American, Eurasian and African Plates.

The Algar do Carvão is essentially an ancient lava tube, made up of a volcanic chimney, about 80-90 metres deep, which then opens up into secondary magma chambers. The chimney formed first roughly 3,200 years ago, in the wake of a volcanic eruption. Then a second eruption, occurring in the same spot 1,200 years later, created many of the magma chambers seen today.

A profile of the Algar do Carvão, based on a similar cutaway produced by “Os Montanheiros,” (Credit: Ruben JC Furtado / Wikimedia Commons)

Despite what the cavern’s title suggests, the volcanic site is not a source of coal, but rather named for the walls’ dark black, ‘sooty’ colour. The volcanic pit is actually better known by geologists and cave enthusiasts for its source of silica-rich stalagmites and stalactites, a feature not commonly found in this region. Scientists have hypothesized that the structures’ silicate composition could have come in part from the volcano’s past hydrothermal activity or its population of diatoms, microorganisms which contain silica in their cell walls.

As you can see from the lush flora featured in today’s photo, the Algar do Carvão is teeming with life. Vegetation blankets the mouth of the cone structure and many animal populations thrive in the cavern environment. The volcanic pit is also home to several species found only on the Azores islands, like the troglobian spider Turinyphia cavernicola and the Terceira Island scarab Trechus terceiranus.

References

Daza, D. et al.: Isotopic composition (δ¹⁸ O y δD) of silica speleothems of the Algar do Carvão and Branca Opala volcanic caves (Terceira Island, Azores, Portugal), Estudios Geológicos, 70, 2, 2014.

Borges, P. A. V., Carlos Crespo, L., Cardoso, P.: Species conservation profile of the cave spider Turinyphia cavernicola (Araneae, Linyphiidae) from Terceira Island, Azores, Portugal, Biodiversity Data Journal 4: e10274, 2016.

Nunes, J.C., J.P. Constância, M.P. Costa, P. Barcelos, P.A.V. Borges & F. Pereira: Route of Azores Islands Volcanic Caves. Associação Os Montanheiros & GESPEA (Ed.). 16, 2011.

Algar do Carvão, Associação Os Montanheiros

Natural Monument of Algar do Carvão, 2011 Regional Secretariat for Agriculture and Environment, Governo dos Açores

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/.