Journal Article

Inter- and Intra-Catchment Variations in Proglacial Geomorphology: An Example from Franz Josef Glacier and Fox Glacier, New Zealand

Carrivick, Jonathan L., Rushmer, E. Lucy

2009

Overview

Proglacial outwash plains, or \"sandar,\" can be recognized to be a part of a geomorphic, sedimentary, and hydrological system. At a global scale, glacial meltwater regimes and hence proglacial fluvial systems are strongly determined by glacier basal water conditions and glacier behavior. At a catchment scale it is necessary to consider that proglacial fluvial sedimentation can have a range of frequency and magnitude regimes. This paper presents geomorphological and sedimentological data from Franz Josef Glacier and Fox Glacier sandar, which have adjacent catchments. We determine that glaciofluvial facies are the most abundant sediment-landform association at both sites. However, we also observe considerable intra-catchment variability with respect to the magnitude-frequency regime of fluvial deposition and the relative importance of fluvial processes for sandur character. Franz Josef Glacier sandur is relatively high relief and superficially composed of boulder bedforms that are laterally and longitudinally extensive. It has a sedimentology dominated by massive, poorly sorted sediments containing outsized clasts. Franz Josef Glacier sandur thus has a character consistent with formation by episodic high-magnitude fluvial flows, i. e. jokulhlaups. In contrast, Fox Glacier sandur is of low cross-section relief and comprises two distinct components: an aggrading braided river and paraglacial debris fan deposits. With the exception of the contemporary ice margin, Fox Glacier sandur is of significantly finer-grained material than that at Franz Josef Glacier. We suggest that the contemporary Fox Glacier sandur contains widespread evidence that refutes a hypothesis of highmagnitude episodic events. Additionally, contemporary paraglacial inputs from recently deglaciated valley walls at Fox Glacier are far more important to sandur sedimentation than water or sediment from Fox Glacier. These results present a conceptual model of the predominant contemporary land-forming processes within a glaciated technically active region with exceptionally high denudation rates. Intracatchment variability has important implications for predicting sediment fluxes in response to hydro-climatic forcing.

• Publisher: Institute of Arctic and Alpine Research
• Subject: Alpine glaciers / Boulders / Geological facies / Geomorphology / Glacial landforms / Glaciers / Gravel / Including Selected Presentations from the Second SEDIBUD Workshop, Abisko, Sweden, September 2007 / Moraines / Sediments / Watersheds