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Lake shoreline deformation in Tibet and mid‐crustal flow

The central Tibetan Plateau shows internal drainage and despite its low rainfall, contains abundant lakes (Fig. 1). These lakes were once much more extensive and their former outlines can be seen in ancient shorelines (Fig. 2). Access can be difficult, altitude sickness can be a hindrance and the weather at 5000 m can suddenly turn cold (Fig. 3), but fieldwork in Tibet rewards with opportunities for cutting-edge research. Due to the slow erosion rate and sparse vegetation, the lake shorelines in Tibet are well preserved and represent a set of outstanding markers of old lake levels that define the paleo-horizontal (Fig. 4). Any deviation from horizontal represents subsequent vertical displacement, reflecting tectonic processes. Despite their research potential, the lake shorelines of Tibet have been little studied. Our recent field survey focused on one of the largest lakes, Nam Co (e.g. Matthews et al. 2004). The aim was to look for sloping shorelines that represent a viscoelastic response to the reduction in water load produced by shrinking of the lakes. In combination with absolute ages, this information can be used to quantify the amount and rate, and hence effective viscosities, of any mid-crustal inflow. The processes linking lake shoreline slopes to movements in the crust and mantle can be termed ‘lake tectonics’. Here we show examples of these shorelines and material that can be used for dating (Fig. 5). *Correspondence.