Landforms and Quaternary surface deposits evolution in Half Moon Island, South Shetland Islands

Abstract:

In this work we present a geomorphological map, originally to 1:10 000 scale, 14 profiles of raised beaches, and an interpretation of the geomorphological evolution of Half Moon Island based on the analysis of the landforms and the surface deposits. Marine landforms are the more characteristic features of the island. The present shape is the result of the linking, during the Quaternary, of three little islands by means of two tombolos. Three main groups of marine landforms and deposits have been distinguished: upper platforms (70-90 m), middle platforms (approx 40 m) and lower raised beaches (<18 m). The two first platforms are pre-Holocene and the third group is Holocene. Glacial processes have retouched the upper zones and periglacial landforms have recently occupied the deglaciated areas. There are two residual ice masses, both remains of a previously existing glacial dome located on the platform between Xenia and Cerro Gabriel. This glacier left tills and moraines, probably corresponding to the Little Ice Age readvance. Periglacial landforms and processes are relatively important at present, with active and inherited landforms. Seven different types of periglacial landforms, located on beaches and marine platforms, have been inventoried. All of them are located above 10 m a.s.l., and are dominant above 18 m a.s.l., where patterned ground reach wide development. Periglacial processes have today a reduced activity. Seven main morphogenetic phases have been recognised, and the geomorphological evolution of the island schematized in four sketches. Phase 1 (F1) suppose a general erosion and shapes the upper platforms. During F2 the platforms are eroded, and in F3 several little islands exist, all this phases are pre-Holocene. A Holocene accumulation phase permitted the construction of the tombolo connecting Xenia-Gabriel and La Morenita (F4). A new raising (F5) is the origin of up to 14 levels of raised beaches. In this period the tombolo connecting La Morenita and Cerro Baliza was built. By correlation with the regional chronology stablished by other authors, the age of F4 could be 5000-6000 years BP, and 1900-2200 years BP the Cerro Baliza connection in F5. The glaciers existing in the upper area show a recent advance (F6), post 800-500 years BP according with the regional chronology, accompanied of an increase of the periglacial action in lower areas. The Equilibrium Line Altitude (ELA) was at 70-90 m a.s.l. during the Little Ice Age, being today above 90 m. The present ice margins show a retreat of the glaciers in relation to their previous positions (F7).

Año de publicación:

1997

Keywords:

Fuente:

scopus