Bathymetry of Lake Constance – a High-Resolution Survey in a Large, Deep Lake

Within the project “Tiefenschärfe – hochauflösende Vermes- sung Bodensee” a high-resolution seamless terrain model is created using airborne topobathymetric laserscanning and multibeam echosounder (MBES) techniques. The project visu- alizes the enormous wealth of features of underwater land- scapes of lakes. The combination of hydroacoustic (multibeam echosounder) and laser-optic (topobathymetric laserscan- ning) methods was used for the first time in a freshwater body of this size. Opportunities, limitations and restrictions of these high-resolution methods are presented.

Possible earthquake trigger for 6th century mass wasting deposit at Lake Ohrid (Macedonia/Albania)

Abstract. Lake Ohrid shared by the Republics of Albania and Macedonia is formed by a tectonically active graben within the south Balkans and suggested to be the oldest lake in Europe. Several studies have shown that the lake provides a valuable record of climatic and environmental changes and a distal tephrostratigraphic record of volcanic eruptions from Italy. Fault structures identified in seismic data demonstrate that sediments have also the potential to record tectonic activity in the region. Here, we provide an example of linking seismic and sedimentological information with tectonic activity and historical documents. Historical documents indicate that a major earthquake destroyed the city of Lychnidus (today: city of Ohrid) in the early 6th century AD. Multichannel seismic profiles, parametric sediment echosounder profiles, and a 10.08m long sediment record from the western part of the lake indicate a 2m thick mass wasting deposit, which is tentatively correlated with this earthquake. The mass wasting deposit is chronologically well constrained, as it directly overlays the AD472/AD 512 tephra. Moreover, radiocarbon dates and cross correlation with other sediment sequences with similar geochemical characteristics of the Holocene indicate that the mass wasting event took place prior to the onset of the Medieval Warm Period, and is attributed it to one of the known earthquakes in the region in the early 6th century AD.

Hydroakustische Methoden. Möglichkeiten und Grenzen zur Langzeitüberwachung archäologischer Denkmale im Flachwasser

Hydroakustische Methoden werden oft zur Vermessung von archäologischen Fundstellen und zur Objektsuche in der Flachwasserzone von Seen und Flüssen eingesetzt. In diesem Beitrag werden die technischen Grundlagen hydroakustischer Messverfahren erläutert und eine kurze Beschreibung üblicherweise eingesetzter Mess- geräte gegeben. Anschließend zeigen wir Beispiele von Vermessungen mit unterschiedlichen Singlebeam-Echo- loten, Multibeam-Echoloten, einem Sidescan-Sonar und einem Interferometrischen Sonar. Mit den Arbeiten aus dem Bodensee, Zürichsee und dem Vierwaldstättersee werden die Möglichkeiten und Grenzen der Hydroakus- tik in der Binnengewässerarchäologie erläutert.

Bathymetry of Lake Constance - State-of-the-art in surveying a large lake

In 2014 the by far largest German lake has been newly surveyed. The transnational project is funded by the European Union and delivers a detailed 3D-model of the lake- floor. The German project name is »Tiefenschärfe – Hochauflösende Vermessung Bo- densee«, which in English roughly means: high-resolution survey of Lake Constance. The German term »Tiefenschärfe« (in optics and photography: depth of field) plays with the meanings of »Tiefe« (depth) and »Schärfe« (sharpness). The result of the sur- vey shall be a clear and sharp image of the deep and shallow lake- floor. At present the LiDAR and multibeam data are still processed, but first results are presented in this article.

Earthquake- induced Geomorphology: A Neotectonic Study at the Front of the Alps (Lake Thun & Aare Valley, Switzerland)

We present a multi-disciplinary two-step approach to assess the potential for seismic hazard of the Aare valley and perialpine Lake Thun (Switzerland). High-resolution seismic images and multibeam-bathymetric data, complemented by field observations represent the tools to identify potentially active seismogenic fault structures. Several second-order earthquake effects such as subaqueous mass movements, seismites and liquefaction structures have been observed in Lake Thun and ultimately document the seismic activity of the study area. A first investigation of possibly first-order active structures is presented in the scope of this study. Recently acquired bathymetric data in Lake Thun reveal significant morphologic depressions aligning with an observed lineament on land. Furthermore, high-resolution seismic images indicate potential fault structures in Lake Thun. However, their continuation with depth has to be verified with a multichannel seismic campaign, scheduled for March 2015.