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Models of Thermal Erosion

Costard (100%), L. Dupeyrat (100%), J. Gargani (100%), Doctorants et post-doctorants : M. d’Olce, A. Séjourné ITA-IATOS : E. Carey-Gailhardis IE, Ch. Marmo IR Collaborations extérieures: D. Gobin (FAST) - E. Gautier, D. Brunstein (Geog. Phys. Meudon) E Mouche, O Grenier (CEA-IPSL) - A. Fedorov, (Permafrost Institue, Yakoutsk), D. Yang (Univ. of Fairbanks, USA).

1 - The program MANET

The MANET program (Analogical and Theoretical Modelling of Thermal Erosion) aims at studying the flows in periglacial environment and their effects on the processes of thermal erosion on Earth and on Mars. The program includes a first part of theoretical modelling (collaboration FAST) which aims at determining the coefficients of convective heat transfer between a water flow and permafrost, and the erosion rate in order to obtain a model at variable rate of the thermal transfers between an ice-cold bank and a river. An analogical modelling of the process of thermo-mechanical erosion was realized with the installation of a hydraulic channel placed in a cold room. This experimental simulation allowed to establish a hierarchical organization of the parameters influencing the efficiency of the thermal erosion. This whole program MANET was realized within the framework of the thesis of R. Randriamazaoro supported in 2007.

Fig. 1: Experiments of thermal erosion in a cold room

These models are then validated by measures on the ground and by means of satellite images applied to the study of Lena in Central Yakutia. So, we set up a program of research with the Laboratory of Physical Geography of Meudon and the Permafrost Institut ( Yakutsk) on a diachronic study of the river reliefs of Lena. A study SIG of the recession of islands in the upstream sector of Yakutsk allowed to bring to light an increase of the recession of banks at the head of islands. An analysis of thermal data (temperature of the Lena river in May and June) and hydrologics (discharge of the Lena river) show clearly the impact of the recent global warming on the efficiency of the process of thermal erosion exercised against the banks of Lena in Central Yakutia. This work was published in GRL and was the object of a press release of the CNRS(NATIONAL CENTER FOR SCIENTIFIC RESEARCH) in 2007

2 - The program CLIMAFLU

Within the framework of the ANR CLIMAFLU " RIVER dynamic of the CLImatic and Lena to rivet), we were able to set up a program of research with Permafrost Institut (Yakutsk). The first results show clearly the impact of the recent global warming on the efficiency of the process of erosion thermodynamics exercised against banks. A study SIG of the recession of 33 islands in the upstream sector of Yakutsk allowed to bring to light an increase of the recession of banks at the head of islands since the 80s. An analysis of thermal data (temperature of Lena in May and June) and hydrologics (discharge during flooding) show clearly the impact of the recent global warming on the efficiency of the process of thermal erosion of river banks. Besides, the analysis of monthly climatic and hydrological data to Yakutsk showed a sensitive increase of the temperature of the water of Lena to Tabaga (upstream sector of Yakutsk).

In July, 2007, a publication in GRL (Costard and al ., 2007) brought to light the impact of the recent warming on the increase of the thermal erosion of fluvial islands . The CNRS(NATIONAL CENTER FOR SCIENTIFIC RESEARCH) made widely the echo of this publication on its Web site with a press release.

Figure of a bank composed of permafrost undergoing an erosion of 30 m/year

The object of this project is a study of the conditions of ice break up and their temporal variability according to the climatic and hydrological parameters. In Siberia, the Lena river presents a rather strong variability of the break up regime from one year to the next. The conditions of initiation of ice break up, their intensity and their efficiency on the erosion of banks remain still poorly understood. We wish to approach this problem by a temporal and spatial high-resolution study of the conditions of initiation of ice break up. The purpose is to confront, for a given year, the information resulting from hydrological and climatic data on the intensity of the ice break up. The detailed analysis of these data should supply us with elements of answer on the favorable conditions of initiation of the strong ice break up registered these last 30 years.





IDES Université Paris-Sud 11 CNRS Faculté des Sciences
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