Plunging folds

Folds with inclined fold axis are called plunging folds. Determining the plunge and plunge direction can be a quite tricky task, if the exposure is 2-D. The photograph below shows plunging folds developed in glacial ice ("Pasterze", the largest glacier in Austria; 2.5cm diameter coin for scale). At the surface of the glacier it is impossible to determine the plunge of these folds. However, inspection of the cross sections provided by the crevasse in the centre of the photo gives the correct answer. The folds plunge towards the left!

plunging folds in ice

The models illustrate the difficulties that arise in the interpretion of the map pattern of plunging folds. You will find out that the map of a plunging syncline can look exactly the same as the map of an plunging anticline, if the sequence is a simple 'two-rock' multilayer. For completeness a model with horizontal fold axes is also available.

plunging folds

  • Syncline and anticline

  • Plunging syncline and anticline

  • Plunging syncline

  • Plunging anticline