Investigating thickness and internal structure of alpine mires using conventional and geophysical techniques

We investigated the thickness and composition of five small alpine mires in Tyrol (Austria), performing a combination of conventional techniques (telescope rods, drilling) and geophysical methods. GPR surveys were carried out using 100 and 200 MHz antennas. Geoelectrical profiles supplemented the GPR at two sites; the 2D-surveys were enhanced by additional 1D-profiling. The aim was to achieve data on mire thickness, to cross-check the methods and to find reasons for different performance at the five sites. The investigations contribute to establishing a future protection concept.The formation history of the mires probably goes back to the early Holocene. The three larger mires are terrestrialisation mires, while two mires are formed by paludification. Probing with a metal rod was subject to considerable errors in both directions caused by obstacles and soft underlying layers. Thus, GPR proved to be a favourable addition to conventional depth assessment. At four of five sites, GPR made it possible to depict the base layer of the mires at a high accuracy, while detecting peat internal interfaces was less successful. 2D-resistivity profiling supplemented with 1D-modelling provided excellent additional information on mire base and deeper subsurface; at one site where minerogenic material is washed in, 2D-resistivity proved to be the better choice compared to GPR.