Geobulletin alpha

December 3rd - Geology of Anglesey 

Bath Geological Society - December 3rdThe Geology of AngleseyDave Green, GeostudiesFor years the geology of Anglesey has caused controversy amongst those studying its complex arrangement of seemingly unrelated fault blocks, particularly the status of the PreCambrian (or are they?) granites and gneisses, sedimentary extrusive sequence, blueschists, ophiolitic/deep ocean facies and melange. So complex that the very stratigraphy has been completely overhauled and re-interpreted twice during the [...]

Nature's Seismometers 

In order to make sense of the sediment cores that can be retrieved from lakes near to the Alpine Fault such as Lake Christabel, it is worth having a think about what happens to the environment when the fault ruptures in a large earthquake. Under normal conditions, alpine lakes fill up very slowly with sediment that is fed into them by rivers. The particles settle onto the lake bed gradually, to create a sequence of finely layered mud.When an earthquake occurs, a number of consequences affect [...]

Lake Christabel 

This is Lake Christabel in New Zealand's South Island. It is one of the many beautiful alpine lakes  to be found close to the Alpine Fault. Lake Christabel was formed when a huge landslide blocked the valley, thus damming the river that then backed up to form the lake.The present day outlet runs over the old landslide deposit of large chaotic boulders. Hidden beneath the waters of Lake Christabel are very distinctive sediment layers that tell the story of huge earthquakes that rocked the [...]