Floods and water availability reconstructions from speleothems through Laser-induced break down spectrometry (LIBS) with implications for archaeological work and citizen engagement in the UNESCO global geopark Famenne-Ardenne.

Our work on a speleothem in the Hotton cave reveals a 5000-year record of past floods in the Hotton cave through deposition of detrital layers in a flowstone covered by mud during the exceptional 2021 flood. The palaeorecord reveals other such exceptional floods around 1550 CE (Common Era), 30 CE and 350 BCE (Before Common Era). Further down, a period between 3.3 BCE and 2.6 BCE shows ‘dirty calcite’ with several smaller detrital layers indicating a period with much more regular floods. In the frame of the Leap Project (learning from the past - The impact of abrupt climate changes on society and environment in Belgium - www.leap-belgium.be), we investigate possible relations between the environmental  changes and past human activities. In order to construct high resolution trace element curves as a proxy for past water availability, a procedure for LIBS analysis of speleothems is set up at the Institute of Natural Sciences in Brussels, Belgium. A 2D spectral image of a few millimeters broad is taken along the growth axis of the speleothem. A curve is constructed by averaging the data along horizontal lines of the 2D analysis. It is a rapid and minimal destructive method to obtain trace elemental curves of Mg, Sr, Ba, and other elements such as Pb, Cu, Zn,.. Up to now the method is rather qualitative, but a semi-quantitative analysis is in progress.

The interest of these climate and environmental related data, is that they are very visual, concrete traces of past climate changes. Speleothems and their records of floods are a strong educational tool for citizens that feel not concerned about climate change. The dissemination of our results through events organized by the UNESCO Global Geopark Famenne-Ardenne aims at engaging inhabitants with climate science and awareness.