Public Lectures on the Mathematics of Earth Sciences

Groningen, Thursday November 30, 2006.

A. Deusinglaan 1, Medische Wetenschappen, Boeringzaal

16:00 Brenny van Groesen (University of Twente), Tsunami modelling and simulation from excitation to run-up

Abstract

The devastating North-Sumatra (Aceh-Andaman) tsunami of 26th December 2004 increased the interest in this special natural phenomenon. In this lecture the ma jor ingredients are reviewed and it will be emphasized that many aspects are still only poorly understood.

After some seismological background, we describe the characteristics of such large scale waves that are generated by tectonic plate motions. It will be argued that for coastal areas that are close to the generation region, Tsunami Early Warning Systems can greatly profit from accurate, pre-calculated scenarios of tsunami generation and propagation to the coast; an advanced simulation tool based on a new variational wave model will be discussed. Furthermore, the phenomenon of ’tsunami wave guiding’ will be introduced and the greatly enhanced wave amplification will be calculated theoretically and numerically. Most applications are motivated by the geographical situation of Indonesia, and part of the research is executed in collaboration with Indonesian scientists.

17:00 Leo Maas (NIOZ), Is fair weather drowning caused by dead-water?

Abstract

Every summer, a number of people get into trouble when swimming across a lake. Unfortunately, in some cases people actually drown. The strange thing is that the persons concerned were generally quite capable swimmers, and also the distance, the diameter of the lake, was considered manageable. Even stranger is that these accidents often happened on nice, sunny days. It is clear that we are here not dealing with a real classical research question. But this societal drama is a topic which students may yet find interesting, as we need to proceed as a kind of scientific detective: are there relevant hydrodynamical aspects to the problem? Indeed, we will offer the suggestion that these swimmers may have suffered from dead-water. The phenomenon of ‘dead-water’ is wellknown in nautical history, where it refers to a ship being suddenly brought to a stand still. The conditions under which this happens will be discussed and relevant historical and anecdotal evidence will be given, along with some laboratory experiments directly demonstrating dead-water. But still, do swimmers actually experience difficulties because of this? To test this hypothesis we did an experiment in a swimming pool, the results of which will be discussed.

Broerstraat 5, Academiegebouw, Senaatskamer

20:00 Hans Oerlemans (Utrecht University), Nonlinear dynamics of glaciers

Abstract

Many glaciers appear to react smoothly to changing climatic conditions. However, some classes of glaciers exhibit distinct nonlinear behaviour which is not directly related to external forcing. Surging glaciers forms such a class. These glaciers advance periodically within a relatively short time, with quiescent phases in between. The behaviour can be regarded as a kind of relaxation oscillation. Tidewater glaciers, which are glaciers calving into a fjord or estuary, show nonlinear behaviour of a different type. The calving flux at the glacier front is strongly related to the water depth. Due to large sedimentation rates this water depth is strongly influenced by the glacier motion itself, which generates a nonlinear feedback. In the seminar some basic concepts pertaining to the behaviour of glaciers will be introduced. Next the nonlinear phenomena will be illustrated by examples from real glaciers, and simple modelling approaches will be discussed.