Scientists obtain new data on the weather 10,000 years ago from sediments of a lake in Sierra Nevada

University of Granada researchers are collecting samples in an Alpine lake in Sierra Nevada (Granada). -  UGRdivulga
University of Granada researchers are collecting samples in an Alpine lake in Sierra Nevada (Granada). – UGRdivulga

A research project which counts with the participation of the University of Granada has revealed new data on the climate change that took place in the Iberian Peninsula around the mid Holocene (around 6.000 years ago), when the amount of atmospheric dust coming from the Sahara increased. The data came from a study of the sediments found in an Alpine lake in Sierra Nevada (Granada)

This study, published in the journal Chemical Geology, is based on the sedimentation of atmospheric dust from the Sahara, a very frequent phenomenon in the South of the Iberian Peninsula. This phenomenon is easily identified currently, for instance, when a thin layer of red dust can be occasionally found on vehicles.

Scientists have studied an Alpine lake in Sierra Nevada, 3020 metres above sea level, called Rio Seco lake. They collected samples from sediments 1,5 metres deep, which represent approximately the last 11.000 years (a period known as Holocene), and they found, among other paleoclimate indicators, evidence of atmospheric dust coming from the Sahara. According to one of the researchers in this study, Antonio García-Alix Daroca, from the University of Granada, “the sedimentation of this atmospheric dust over the course of the Holocene has affected the vital cycles of the lakes in Sierra Nevada, since such dust contains a variety of nutrients and / or minerals which do not abound at such heights and which are required by certain organisms which dwell there.”

More atmospheric dust from the Sahara

This study has also revealed the existence of a relatively humid period during the early phase of the Holocene (10.000 – 6.000 years approximately). This period witnessed the onset of an aridification tendency which has lasted until our days, and it has coincided with an increase in the fall of atmospheric dust in the South of the Ibeian Peninsula, as a result of African dust storms.

“We have also detected certain climate cycles ultimately related to solar causes or the North Atlantic Oscillacion (NAO)”, according to García-Alix. “Since we do not have direct indicators of these climate and environmental changes, such as humidity and temperature data, in order to conduct this research we have resorted to indirect indicators, such as fossil polen, carbons and organic and inorganic geochemistry within the sediments”.

New areas prone to moderate earthquakes identified in Iberian Peninsula

The map indicates the nodes (circles) with the potential to generate moderate earthquakes in the Iberian Peninsula and earthquakes historically (blue dots) of this magnitude. -  A. I. Gorshkov  et al.
The map indicates the nodes (circles) with the potential to generate moderate earthquakes in the Iberian Peninsula and earthquakes historically (blue dots) of this magnitude. – A. I. Gorshkov et al.

Some areas of the Iberian Peninsula, where earthquakes of moderate magnitude have never yet been recorded, such as certain parts of the Cordillera Cantábrica mountain range, the far west of the Cordilleras Béticas mountains and the north of Valencia, could have the potential to generate such quakes, according to a study produced by Spanish, Russian and Italian scientists and published this month in the journal Rendiconti Lincei.

“The methodology we have used confirms the most seismically significant areas of the Iberian Peninsula, but also identifies possible sources of earthquakes with magnitudes of over five in some areas where, to date, none have been recorded” Mariano García-Fernández, co-author of the study and a researcher at the Spanish National Museum of Natural Sciences (CSIC), tells SINC.

According to the study, which has been published in the latest issue of the journal Rendiconti Lincei, these areas are located in some parts of the Cordillera Cantábrica mountain range, the northern coast of Portugal, the far west of the Cordilleras Béticas mountains and the north of Valencia. The remaining areas with the potential for moderate seismic activity are the same as those shown on seismic maps – around the edges of the Peninsula, above all the south east and the Pyrenees.

“The important thing about this study is that it identifies zones prone to moderate earthquakes at regional level, although this does not mean they will ever happen”, points out García-Fernández.

The researcher explains that the magnitude 5 was chosen as the threshold for potential earthquakes “since it is above this level that you start to see significant damage to structures”.

In search of nodes

The research, which is the fruit of collaboration between scientists at the Russian Academy of Sciences, the International Centre for Theoretical Physics and the University of Trieste (Italy) and the CSIC, is based on the morphostructural zoning method. The technique uses topographic, geological and geophysical information, along with satellite imagery, to identify the nodes or intersection points of morphostructural lines.

These nodes are classified as likely to cause earthquakes of a specific threshold size by combining the seismicity data from seismic catalogs with mathematical recognition methods, similar to those used in voice or fingerprint identification.

García-Fernández insists that the resulting classification does not necessarily mean that the potentially seismic nodes identified will produce earthquakes of this size, “but rather that their features make them more susceptible than those classified as having lower potential”.

The authors of the study are confident that the results will make it possible to better identify the continental seismogenic sources affecting the Iberian Peninsula. This will allow progress to be made in studies into danger levels and seismic risk at regional scale and in specific places, such as metropolitan areas or special structures such as nuclear power plants and large dams.