Antiscarp initiation and evolution
Thesis DisciplineEngineering Geology
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Antiscarps are defined here as any uphill facing scarp that may be observed on slopes, regardless of size or scale. They are not present on all slopes, but where they have been observed, they typically occur sub-parallel to the valley axis near the ridge crests in mountainous regions. Antiscarps are generally, but not exclusively, found in glaciated regions, where loading and unloading of the rock mass has effected changes to the in situ stress fields through cycles of compression and elastoplastic rebound and has also removed large volumes of material by the formation of cirques. Non-glacial antiscarps are commonly associated with tectonic activity. An extensive review of current literature has been used to assist in the identification of key parameters associated with antiscarps and to provide a basis for clearly defining the terminology used to address antiscarp related processes and features. All of the reviewed material has been collated into a chart where the factors that have been extracted from the articles are grouped and compared. The chart has been instrumental in selecting the nomenclature to be used when addressing different types of antiscarp and also in constraining the extent to which the term can be reasonably used. A flowchart has been developed to assist in the identification of the primary antiscarp forming process. The flowchart was successfully used to identify the primary processes associated with antiscarps observed in field studies in both the South Island of New Zealand and in the Scottish Highlands. Physical base friction models and numerical finite element modelling, using Plaxis v6.1 and FLAC 2D v3.40, both indicate that antiscarps can form solely under a gravitational load. Base friction models used individual elements of various geometries. Antiscarps formed in most of the models and were best identified in models that had a clearly defined discontinuity surface. The numerical models also indicate that shear along existing discontinuities is the dominant mode for the formation of antiscarps under a gravitational load in homogeneous massifs.