Alluvial fans as an indicator of Quaternary climate change

Autor(en)

Frank Lehmkuhl, Janek Walk, Owen Lewis

Abstrakt

Past research suggests that alluvial fans are, due to their direct coupling to the source area, sensitive to Quaternary environmental change and, thus, provide essential archives for paleoenvironmental conditions, notably climate, hydrology, and tectonics. Although they have been studied for many decades across the globe, there is no unifying scheme to view their variety in relation to the formative geomorphological regimes. The spatial and temporal approach in geomorphology indicates that the development of landforms is a function of size and time. While small-scale landforms are created by short-term events, mesoscale and macroscale landforms develop within a period of 104 to 105 years. A conceptual model for the formation of alluvial fans is developed, and their implication for Quaternary climate change is assessed, using a review of their global range and data from selected key dryland regions. We propose three main depositional regimes for alluvial fan development: i) Mountain alluvial fans, small in size and extent; ii) mesoscale pediments and bajada of (semi-) arid regions; and iii) mega fans mainly associated with Cenozoic mountain building.

Mountain alluvial fans are governed by cryogenic and nival processes, closely linked to climate change, tectonic processes such as earthquake-triggered landslides, and are often also modified by anthropogenic intervention. In drylands, mesoscale pediments and bajadas are one of the most common fluvial systems and landform features, where they are frequently associated with steep mountain fronts, closely related, and often modified by active tectonics. The formation of mesoscale alluvial fans occurs in different settings characterized by distinct relationships between sediment production and transport capacity. Although governed primarily by the climatic setting, bedrock geology can be the dominating factor, especially for sediment production. Alluvial fans in the drylands of the western United States, Mongolia, Chile, and Namibia illustrate the links to climate variability by glacial-interglacial cycles or expressed in late Quaternary pulses of increased humidity. Furthermore, mesoscale alluvial fans are common in glaciofluvial and periglacial settings, where streams have high bedload and transport capacity depending on a sediment supply especially due to frost weathering and discharge by snow and ice dynamics.

Organisation(en)

Institut für Geographie und Regionalforschung

Externe Organisation(en)

North Carolina State University, Rheinisch-Westfälische Technische Hochschule Aachen

Publikationsdatum

2023

ÖFOS 2012

105404 Geomorphologie, 105121 Sedimentologie, 105408 Physische Geographie

Sustainable Development Goals

SDG 13 – Maßnahmen zum Klimaschutz

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/012bf372-232d-48c9-b74c-6d23faa6eef5