GeoLog

This week, Imaggeo on Mondays is brought to you by Josep Ubalde, who transports us to a wonderful site in western Turkey: a city of hot springs and ancient ruins dubbed cotton castle, after the voluminous white rocks that spread from the spring’s centre…

Pamukkale is lies in Turkey’s inner Aegean region, within an active fault that favours the formation of hot springs. The spring’s hot waters were once used by the ancient Greco-Roman city of Hierapolis, the remains of which sit atop Pamukkale. The entire area – city, springs and all – was declared a World Heritage site in 1988.

Travertine terraces in Pamukkale, Turkey (Credit: Josep M. Ubalde via imaggeo.egu.eu)

The materials that make up Pamukkale are travertines, sedimentary rocks deposited by water from a hot spring. Here, the spring water follows a 320-metre-long channel to the head of the travertine ridge before falling onto large terraces, each of which are about 60-70 metres long.

The travertines are formed in cascading pools that step down in a series of natural white balconies. These travertines are 300 metres high and their shape and colour lend them the name Pamukkale, meaning “cotton castle”.

At its source, the water temperature ranges between 35 and 60 degrees Celsius, and it contains a high concentration of calcium carbonate (over 80 ppm). When this carbonate-rich water comes into contact with the air, it evaporates and leaves deposits of calcium carbonate behind. Initially, the deposits are like a soft jelly, but over the time they harden to form the solid terraces you see here.

Putting Pamukkale into perspective (Credit: Josep M. Ubalde)

These travertines have been forming for the last 400,000 years. The rate they form is affected by weather conditions, ambient temperature, and the duration of water flow from the spring. It is estimated that 500 milligrams of calcium carbonate is deposited on the travertine for every litre of water. Today, thermal water is released over the terraces in a controlled programme to help preserve this natural wonder. You can no longer walk on them, but they are beautiful to behold.

By Josep M. Ubalde, Soil Scientist, Miguel Torres Winery

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

Wildfires frequently break out in the Californian summer. The grass is dry, the ground parched and a small spark can start a raging fire, but burning can begin even when water is about. Gabriele Stiller sets the scene for a blaze beside Mono Lake, exploring the events that got it going and what it may have started in the sky… 

While on shores of Mono Lake in the summer of 2012, I spotted something strange in the distance: a great blaze on the other side of the lake. We were on a trip through the southwestern states (a long tour through California, Nevada, Utah and Arizona). All the days before we had been continuously accompanied by thunderstorms that broke out during the afternoon. The photo was taken before the daily thunderstorm, and the large convective system already hinted to the next storm to come – and indeed it did, just a few hours later.

Desert fires close to Mono Lake, California. (Credit: Gabriele Stiller via imageo.egu.eu)

It was not clear if this convective cloud system was generated by uplift of heated air initiated by the fire, a process known as pyro-convection, or if it was simply a coincidence. After all, thunderstorms were a regular occurrence throughout our trip. This could have been the storm of the day, and the related convection could have transported the air and smoke from the fire upwards. Or a combination of both could have been behind it. The cumulus cloud was quite isolated, with clear sky surrounding it, but you can already see a small anvil developing (the area where ice is formed in the cloud) above the cauliflower-like cumulus – a hint towards a developing thunderstorm. Such a development would make the cloud into a cumulonimbus cloud.

So what caused the blaze? On 8 August 2012, the wildfire was started through lightning ignition by a thunderstorm coming from the Sierra Nevada, and it burned for several days on open grassland, far from human infrastructure. Due to these circumstances, firefighting was not particularly difficult for the authorities. However, more than 13000 acres were burned, and more than 500 people fought the fire. One of the priorities was to keep the amount of sage-grouse habitat burned to a minimum.

By Gabriele Stiller, Karlsruhe Institute of Technology, Karlsruhe, Germany

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

Extreme weather events, like catastrophic floods, are the malicious exclamation points of Earth’s chaotic and variable climate system; they arrive without warning and extract huge costs, both economic and humanitarian, from the communities they strike. Evidence suggests the frequency and severity of these events may be on the rise in a changing climate, but scientists struggle to place modern events in a longer historical context.

Information about the past hides in all kinds of places. The trick is figuring out how to extract it. Rudolf Brázdil and his team from Masaryk University in Brno have started using historical tax records from southern Moravia in the Czech Republic to reconstruct the flood history of the area, a test case for broader studies of this kind. At the EGU General Assembly, Brázdil sat down with Julia Rosen to explain his approach.

To start with, how did this idea occur to you?

Existing hydrological series based on instrumental records are generally short. To study really disastrous events, which have a long recurrence interval, you cannot use just the period of hydrological measurements, you have to extend it into the past. We are working in the field of historical hydrology using documentary sources to reconstruct past floods and we recognised that we can use this so-called taxation data. In the past, in Moravia, if anybody was affected by any disastrous events – like a flood – they had the opportunity to ask to pay lower taxes. It was a complicated administrative process, and we are studying documents related to this process to reconstruct hydrometeorological events – including floods. The idea is to obtain the longest series of extremes as possible.

A painting from 1846 commemorating the tragic Elbe flood of March 1845 in Ústí nad Labem, NW Bohemia. The peak discharge of this flood was not matched even by the disastrous August 2002 event. (Credit: Museum of the City of Ústí nad Labem, Oil on wood, painted shooting target, catalogue no. U 334)

How do you actually infer flood histories from these data?

Using this data, you can recognise the time and place of an event and its impacts. That’s because the original aim of these documents was to describe damage for which affected people could obtain some tax relief. Generally, you can use flood marks to determine the size of events. For example, people identified the height of the water on the bridge, or on the wall of the house. In Prague (where I have worked before) there is a statue – the head of a bearded man – that was installed in the 15^th century. People have characterised floods with respect to how much of the head was submerged, or if it disappeared entirely, since 1481. People knew, for example, that if the water reached the head, they had to leave their houses.

You also know the flooded area by which villages or settlements have been affected. It is difficult to precisely compare the magnitude of historical floods with recent floods because of the totally different character of rivers in the past. They were not regulated – they had many meanders and the character of the landscape was different as well. But we can still compare events from the point of view of the frequency of floods, their seasonality and impacts.

What are the challenges of working with this kind of data? What are its limits?

Every proxy is limited from different points of view. One limitation of our data is incompleteness, both spatially and temporally. For example, you could have a situation where nobody recorded such events, although this is not so likely when events are really strong. Second, perhaps someone recorded it, but original records were lost in fires or during reorganisation of archives. Third, of course, it is generally qualitative information. You need to understand the nature of these data by collaborating with historians and archivists. I am a climatologist, and for me, it’s extremely important to cooperate with such people because without them, there wouldn’t be any historical hydrology. On the other, they would never use such data for the purposes for which we are using it. It is a classic example of interdisciplinary research.

What did you find? Has the frequency of extreme floods increased or decreased?

We are more or less at the beginning of this project using taxation records in Moravia. I am just now evaluating everything, so it’s difficult for me to say now. However, I can give you an example from Bohemia (the western part of the Czech Republic) where we have worked before using other kinds of documents. There, the 19^th century was an extremely active period for floods, followed by the second part of the 16^th century. The second part of the 20^th century was very quiet in the Czech Lands, there were really no important floods until the disastrous floods of July 1997 in Moravia and August 2002, in Bohemia.

The Long Bridge across the River Svratka in Brno where ice floes accumulated during the flood of March 1830 after the extremely severe winter of 1829-1830. (Reproduction of a colour drawing by Frantisek Richter, Brno City Archives, Collection of graphics, prints and reprints, no. 255R)

What comes next?

For this project, the first step was tax records. The second step is family archives, which sometimes contain better information, and the third step is chronicles, then newspapers, and of course systematic hydrologic and meteorological measurements. This should form the main database to allow us to do our analysis and synthesis. Success will be if we are able to analyse in detail the spatial and temporal variability of hydrometeorological extremes for the last 350 or 400 years and to use this information for estimates of future extremes.

It will also be a success for us if our work gains acceptance within the international community. This will demonstrate that we are presenting new and interesting results and new methodological approaches that might be applicable on a broader scale. I believe these taxation data are available in many European countries and it would help to extend our knowledge about past floods in this area.

By Julia Rosen, PhD, Freelance Science Writer

Acknowledgement:

The project is financed by the Czech Republic Grant Agency.

This week in GeoTalk, we’re talking to Claudia Cherubini, a research professor from La Salle Beauvais Polytechnic Institute. Claudia shares her work in hydrogeological modelling and delves into how such models can be used in water management…

Could you introduce yourself and tell us a little about what you’re currently working on?

I am an environmental engineer with a PhD in hydrogeology. After more than four years of post-doctoral activity, I finally got a position as associate professor at LaSalle Beauvais Polytechnic Institute, one of the most reputable schools for engineering geologists in France.

My field of research involves characterising flow and transport phenomena in heterogeneous aquifers. My research interests include also advanced geostatistical methods to model complex spatial patterns of contaminants and quantify risk assessment – something I concentrated on when working as a consultant for the Italian Ministry of Environment and the Apulia Region (southeastern Italy).

Meet Claudia! (Credit: Claudia Cherubini)

During EGU 2012, you received a Division Outstanding Young Scientists Award for your work on hydrogeological models and how they can be used in resource management. Could you tell us a bit more about your research in this area?

Before coming to France, most of my research dealt with the hydrogeology of the fractured limestone aquifer in Apulia and, in particular, with water management in coastal aquifers.

The key study concerning this prize is published in Natural Hazards and Earth System Sciences. Together with my Italian colleague Nicola Pastore, I combined two models – one describing density-driven flow and another describing fault hydrogeology – to find out more about the aquifer system in southern Italy. The coupled models let us work out how this complex aquifer could be exploited as well as determine its vulnerability to seawater intrusion. Vulnerability assessments like these are needed for sustainable planning, both in terms of picking well locations and setting pumping rates.

Fractured aquifers are key water sources for many people around the world, how do your findings relate to sustainable water use in these areas? 

Most of my research deals with modeling groundwater flow and contaminant transport in fractured aquifers. Detailed geological reconstructions are used in hydrodynamic modelling to help interpret flow dynamics and the way contaminants are transported. Hydrogeological modelling is extremely important to optimise water extraction in fractured aquifers, to pin down pollution sources or predict the fate of a contaminant. All of these help decide how to manage areas that have been affected by a pollutant. Due to the complexity of fractured rock aquifers, they are often oversimplified. My research aims to apply discrete models to better describe flow and transport dynamics in these aquifers.

How does knowing more about groundwater help scientists understand the impacts of polluted sites on the surrounding environment?

In fractured-rock aquifers, the fracture’s orientation may cause the contaminant plume to be transported in a direction that diverges from the regional hydraulic gradient. Being able to characterise the dominant fractures in the system is extremely useful for aquifer cleanup.

How can hydrogeologists set up something close to what we might find in nature in the lab?

In fracture formations, multiple scales of heterogeneity may exist and there is the need to characterise them at the core, bench and field scale. There is some degree of skepticism about how representative physical models are of phenomena occurring in field conditions though. Laboratory experiments have the advantage of improving our understanding of physical mechanisms under relatively well-controlled conditions, which is not exactly the case in the field.

Key parts of the lab. (Credit: Claudia Cherubini)

Do you prefer fieldwork or fixing up a laboratory experiment?

I would say probably the second. Dealing with lab experiments concerning fractured media is a matter of creativity and innovation, as there is still a lot to do in this research area.

However, here at LaSalle Beauvais we have set up a hydrogeological platform with an experimental site with 18 boreholes up to 110 m deep, each equipped with piezometers – instruments used to measure liquid pressure, so future directions are oriented towards fieldwork.

What do you enjoy about working in science?

I always felt at ease in science and I have always enjoyed doing research everywhere I go. I currently speak English, German, Spanish, French and obviously Italian (my native language). I spent some research periods abroad: during my PhD at The University of Göttingen Geosciences Centre, and during my post doc at Lawrence Berkeley National Laboratory and at United States Geological Survey in California too.

Finally, what are your research plans for the future?

I work in Picardy (north of France), a region characterised by a fissured chalk aquifer, where the unsaturated zone has been poorly investigated. I am setting up a study with the notable scientist John Nimmo of the USGS, aiming to investigate preferential flow dynamics and their role in recharge within this chalk aquifer.

And I have an Italian PhD student to supervise! She will come here to do laboratory and field experiments on the platform. We also plan to integrate our network into the French H+ observatory, a database for data from a network of highly heterogeneous hydrogeological sites.

Find out more about Claudia’s work on fractured aquifers…

Cherubini, C. and Pastore, N.: Critical stress scenarios for a coastal aquifer in southeastern Italy, Nat. Hazards Earth Syst. Sci., 11, 1381-1393, 2011.

Cherubini, C., Giasi, C. I., and Pastore, N.: On the reliability of analytical models to predict solute transport in a fracture network, Hydrol. Earth Syst. Sci. Discuss., 10, 2013. (currently under open review)

Cherubini, C.: A modeling approach for the study of contamination in a fractured aquifer. Geotechnical and Geological Engineering, 26, 519-533, 2008.

Cherubini, C., Giasi, C. I., Pastore, N.: Evidence of non-darcy flow and non-fickian transport in fractured media at laboratory scale. Hydrol. Earth Syst. Sci., 17, 2599–2611, 2013.

Cherubini, C, Giasi, C. I., and Pastore, N.: Bench scale laboratory tests to analyze non-linear flow in fractured media. Hydrol. Earth Syst. Sci., 16, 2511-2522, 2012.

If you’d like to suggest a scientist for an interview, please contact Sara Mynott.