Geomorphological processes of alluvial fans under climatic and tectonic influence – examples from the SW United States

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Title:Main Title: Geomorphological processes of alluvial fans under climatic and tectonic influence – examples from the SW United States
Description:Abstract: In recent years, significant progress has been made in several scopes of alluvial fan research. Paleoclimatic data has been improved and a sophisticated understanding of the alluvial fan evolution could have been archived. Fans form under a variety of climatic and geomorphic settings and are controlled by superordinate factors including climate and tectonics which in turn influence the driving processes of sediment erosion and deposition. It is generally accepted that tectonic activity both produces and maintains the relief that is required to form a setting of ranges with adjoining valleys and provides sufficient sediment (Robinson et al. 2005; e.g. Harvey et al. 2005; Blair and McPherson 2009). Therefore, tectonics, as a basic condition, affects fan evolution as a long-term control and particularly designates the duration over which fan deposition may occur along the mountain front (Ritter et al. 1993). The main reason why climatic fluctuation of the Holocene and the late Pleistocene has been interpreted in recent alluvial fan research, mainly consists in the progress of dating technology. Because paleoclimatic events can be traced back more and more precisely, the influences of the climate can be interpreted more accurately. Tectonic influences clearly act more constant in this limited period of time and are therefore, erroneously, less considered. For this reason, in alluvial fan research, a clear distinction of whether an alluvial fan is primarily influenced by tectonics or climate is not scientifically reasonable. Early studies recognized alluvial fans to evolve highly episodic (Haas et al. 2014). In recent years, with the help of modern dating methods becoming steadily more precise, researchers have been able to connect significant phases of fan aggregation with climatic variability throughout the Quaternary. (McDonald et al. 2003; Barnard et al. 2006; Quigley et al. 2007; Sohn et al. 2007; Pope et al. 2016). However, the recently emerged consensus on climatic variability as the primary control of alluvial fan aggradation (Quigley et al. 2007; Regmi et al. 2014; Owen et al. 2014; Cesta and Ward 2016; Terrizzano et al. 2017; Mason and Romans 2018) could not eliminate discrepancies within the model itself. Disagreement remains about whether alluvial fans are built up under arid conditions, in humid environments or during a transitional stage in between (D'Arcy et al. 2017). Thus, both short-term events such as the ENSO variability and long-term glacial-interglacial cyclicity were proved to be responsible for active phases of alluvial fans development. Especially in the southwestern of the U.S. there is evidence to suggest that tropical cyclone activity induced by the warming sea surface temperature in the Gulf of Mexico and the Gulf of California promoted fan-constructing processes (Löhrer 2008; Miller et al. 2010; Bacon et al. 2010; D'Arcy et al. 2017). The original approach phrased by Bull (1977) that alluvial fans exclusively form during arid conditions would thus be disputed. Due to further studies, the importance of floods caused by high precipitation intensities increased. It turned out, that the focus of research aims to distinguish between rainfall intensity and the average amount, no matter whether the climatic state is in an arid, humid or a transitional phase (D'Arcy et al. 2017). Episodically occurring alluvial fan aggradation could thus no longer be assigned to a particular climatic state, which would repeatedly push dating methodologies to their limits (Figure 9). Despite the persistent focus by desert geomorphologists on linkages between climatic change and alluvial fan development, there are major limitations to this entire subfield of desert geomorphology. First, fan deposits are not diagnostic of any particular climatic condition, and thus sedimentology and stratigraphy cannot be used as an indicator of climatic change without independent chronometric support. Second, dating methods are not capable of correlating geomorphic events to sub-Milankovitch climatic changes with any degree of certainty (Mason and Romans 2018). Even the latest dating methodologies possess limitations and several sets of uncertainties (Dorn 2009; Bacon et al. 2010). The ability to connect fan-building events to decadal or century-scale oscillations is highly speculative at best. Magnitude and timing of sediment transport and storage is hard to constrain (Miller et al. 2010). Several diverse international theories, based on detailed case study analysis, will offer future investigation ample opportunity to evaluate established and future theoretical options. Current research on alluvial fans is not only relevant in order to reconstruct paleoclimatic conditions, its processes and aggradational dynamics. Recent findings also possess fundamental importance with regard to enhanced precipitation events in the course of climate change (D'Arcy et al. 2017).
Responsible Party
Creator:Bianca Waldapfel (Author)
Contributors:Frank Lehmkuhl (Supervisor), Veit Nottebaum (Supervisor)
Funding Reference:Deutsche Forschungsgemeinschaft (DFG): CRC 1211: Earth - Evolution at the Dry Limit
Publisher:CRC1211 Database (CRC1211DB)
Publication Year:2019
Topic
CRC1211 Topic:Surface
Related Subproject:C2
Subjects:Keywords: Geomorphology, Quaternary Geology, Arid Zone, Landscape Evolution
Geogr. Information Topic:Environment
File Details
Filename:BA_Waldapfel_2018_Processes_alluvial_fans_climate_tectonics.pdf
Data Type:Text - Text
File Size:2.1 MB
Date:Created: 16.07.2018
Mime Type:application/pdf
Data Format:PDF
Language:English
Status:Completed
Constraints
Download Permission:Only Project Members
General Access and Use Conditions:According to the CRC1211DB data policy agreement.
Access Limitations:According to the CRC1211DB data policy agreement.
Licence:[CRC1211DB] Data policy agreement
Geographic
Specific Information - Report
Report Date:16th of July, 2018
Report Type:Bachelor Thesis
Report City:Aachen
Report Institution:RWTH Aachen University
Metadata Details
Metadata Creator:Janek Walk
Metadata Created:13.11.2019
Metadata Last Updated:13.11.2019
Subproject:C2
Funding Phase:1
Metadata Language:English
Metadata Version:V50
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