Tunnel valleys: Genetic models, sedimentary infill and 3D architecture

During its geological history, earth has experienced several periods of extreme cold climate. During these glaciations, ice sheets covered large parts of the globe. Because of the erosive power of flowing meltwater and ice, deep incisions, such as fjords, are an important aspect of the glacial environment. This thesis covers one specific type of incision: so-called tunnel valleys. Tunnel valleys are up to 100 km long, 5 km wide and 400 m deep incisions. These landforms are present, amongst others, in the subsurface of the northern part of the Netherlands where they are associated with the Pleistocene glaciation. However, how these tunnel valleys were formed remains a controversy. Over the previous two decades, tunnel valleys have gained societal importance as the pore space between the sediments filling tunnel valleys frequently contains important resources, such as groundwater and hydrocarbons. For efficient exploitation of these resources it is important to understand how and where tunnel valleys were formed, the controlling factors on their dimensions and how they were filled. Analysis of boreholes and seismic data has provided new insights into the processes that resulted in the formation and infilling of tunnel valleys. It has been shown that tunnel valleys form beneath the outer ice-cap rim during phases of ice-sheet recession. The rate of ice-sheet recession determines the morphology and infilling of tunnel valleys. These insights provide useful predictive criteria for the exploration of resources contained within these landforms.Geoscience & EngineeringCivil Engineering and Geoscience