GEOMORPHOLOGY AND ORIGIN OF THE SURFICIAL SEDIMENTS OF THE ST. BERNARD SADDLE, CASS REGION, NEW ZEALAND

In a world increasingly affected by glacial retreat and the impact that associated sediment supply changes have on river behavior and ecosystems, it is important to consider the influence that these processes leave on past landscapes. This study focuses on the St. Bernard Saddle, a depression in the Southern Alps of New Zealand framed by Mt. Sugarloaf and a terminal moraine left by the Waimakariri Valley Glacier. The area has largely been ignored or mischaracterized in research to-date, creating a gap in the geomorphic history of the Central Southern Alps region. This study aims to improve understanding of the St. Bernard Saddle by determining the origin of the surficial sediments and developing a model for the surficial processes that have impacted the development of the landscape. Field and desktop geomorphic mapping of the study area, along with sediment sampling, description, and laser sediment size analysis, were completed in order to fulfill the study aims. The results suggest that the overlying sediments are loess, likely of periglacial origin. Variation in sediment size indicates that the loess has been modified in some areas by secondary mobilization, followed by a period of soil development during the early Holocene. The sparse vegetation in the central depression today is interpreted as occurring as a result of an increase in fires and grazing due to human settlement, leading to a period of erosion marked by a minimal O horizon today despite earlier soil development. These findings refute the existing characterization of the sediments as glaciolacustrine and strongly emphasize the importance that field work played in identifying the sediments. A thorough and systematic approach to understanding the geomorphology and evolution of a landscape, beginning with field work, is a vital tool in understanding how these landscapes have evolved so that we can consider similar processes acting in environments affected by glacial retreat today.