A glacial geomorphological map of the southernmost ice lobes of Patagonia: the Bahía Inútil – San Sebastián, Magellan, Otway, Skyring and Río Gallegos lobes

Abstract

This paper presents a glacial geomorphological map of the landforms created by five large ice lobes that extended eastwards from the southernmost reaches of the Patagonian Ice Sheet during the Quaternary period. The study is focussed on Tierra del Fuego, but also updates previous mapping of the Skyring and Otway lobes, and the resulting level of detail and extent is a significant advance on previous work in the region. The map has been created as the necessary precursor for an improved understanding of the glacial history of the region, and to underpin a programme of dating glacial limits in the region. It was produced using Landsat ETM+ and ASTER satellite imagery and vertical aerial photography, supplemented by Google Earth TM imagery and field-checking. Eleven landform types were mapped: moraine ridges, subdued moraine topography, kettle-kame topography, glacial lineations, irregular and regular hummocky terrain, irregular dissected ridges, eskers, meltwater channels, former shorelines and outwash plains. The map reveals three important characteristics of the glacial geomorphology. First, the geomorphic systems are largely dominated by landforms associated with meltwater (channels, outwash plains and kettle-kame topography). Second, there is a difference in the nature of landforms associated with the northern three ice lobes, where limits are generally marked by numerous clear moraine ridges, compared to those to the south, where hummocky terrain and drift limits prevail. Finally, cross-cutting landforms offer evidence of multiple advances, in places, which has implications for the timing of limit deposition, and thus for the design and interpretation of a dating programme.

Glacial geomorphology of the terrestrial margins of the tidewater glacier, Nordenskiöldbreen, Svalbard

“…Such a combined approach, linking remote sensing data with direct field observations, has been successfully applied for the mapping of glacial landforms in various environmental settings (e.g. Bennett, Evans, Carbonneau, & Twigg, 2010;Boston, 2012;Brown, Evans, & Evans, 2011;Darvill, Stokes, Bentley, & Lovell, 2014;Evans, Ewertowski, & Orton, 2015a, 2015bEvans, Twigg, Rea, & Shand, 2007;Pearce, Rea, Bradwell, & McDougall, 2014). Geomorphic features were digitised using Esri ArcGIS and stored in a file geodatabase.…”

Glacial geomorphology of the Brabazon & Butler Downs, Rangitata Valley, South Island, New Zealand

“…Meltwater channels typically indicate previous lateral ice-marginal positions (Darvill, Stokes, Bentley, & Lovell, 2014), and are abundant across the Brabazon and Butler Downs; however, many of the meltwater channels are oriented along a southwest to northeast axis, perpendicular to the kettle holes, suggesting that the drainage systems reoriented downslope as the ice sheet pulled back (Soons, 1963), partially obscuring the kame topography in this region.…”

A review of topographic controls on moraine distribution

“…By contrast, surface degradation will have some impact on moraine size (particularly relief) and is discussed in section 4.2.2. Perhaps the most important post-depositional factor in regulating moraine size is dissection, whereby fluvial drainage cuts moraines into segments, producing fragmentary moraine records (e.g., Lovell et al, 2011;Barr and Clark, 2012a,b;Darvill et al, 2014). Generally speaking, dissection is promoted in recently deglaciated landscapes where drainage pathways are poorly established, but is also likely to be more common in laterally unconfined basins where rivers have the opportunity to migrate and bifurcate.…”

“…These topographic steps therefore act as obstacles to flow and are likely to encourage ice margin stability, leading to moraine deposition (Kerr, 1993). An example of this comes from the Skyring and Otway lobes of the former Patagonian Ice Sheet in southernmost South America, which are delineated by closely nested sequences of moraines located on higher ground (Lovell et al, 2011;Darvill et al, 2014), assumed to relate to several glaciations (Kaplan et al, 2009). Here, the ice lobes have been forced to flow through depressions and up reverse slopes, depositing latero-frontal moraines on the edge of the higher ground on several occasions (Fig.…”

“…The record of moraines, as mapped in a given landscape (e.g., Heyman et al, 2008;Lovell et al, 2011;Barr and Clark, 2012a;Fredin et al, 2012;Darvill et al, 2014), is not only an indication of where features were deposited (as outlined in section 3), but also reflects their preservation and ease of identification. A number of moraines have been lost from the record or are unobservable for a number of reasons.…”