What does the sedimentary record tell us about the future of rivers?
Presented by:
Piret Plink-Bjorklund, Colorado School of Mines
with contributions from PhD students
Mark Hansford, Evan Jones, Haipeng Li, Kenya Ono, Jianqiao Wang and Kristi Zellman
Discussion Starts at 12:00 (MT)
Webinar
Abstract
River floods are among Earth’s most common and most destructive natural hazards and have a high impact on society. In the US alone, flood losses reached $20 billion in 2019 (Smith 2020). For comparison, these three 2019 floods cost almost as much as 11 other billion-dollar US disasters combined in 2010-2019 (Smith 2020). In contrast, the impact of major floods on shaping the landscapes, and formation of the sedimentary record is less clear. A common assumption is that moderate (ordinary) events build the sedimentary record, because (1) the high frequency moderate events do more geomorphic work (Wolman and Miller, 1960); and (2) rivers have negative feedback mechanisms, where the effect of high-magnitude events is suggested to be reset during the recovery between these events, due to reworking by moderate events (Costa, 1974; Wolman and Gerson, 1978; Harvey, 2002). These geomorphological assumptions leave us with the understanding that moderate but frequent events are most important in shaping landscapes and forming the sedimentary record. Accordingly, river records are considered extremely normal, were the normalness is represented by ripple laminations, and dune and bar scale cross strata (Paola et al., 2018).
However, there is a large body of work (see references in reviews by Fielding 2006, Fielding et al., 2009, 2011, 2018; Plink-Bjorklund 2015, 2019) that documents river deposits dominated by stacked high-magnitude flood event beds that lack the dune and bar scale cross strata, and rather consist of sedimentary structure to channel scale Froude supercritical flow structures. Such river records seem to be better described by the Derek Ager quote: “The history of sedimentation is like being in the military ... hours of boredom separated by brief moments of terror”.
We will view evidence for both perspectives and discuss: (1) Why do we have this seeming contradiction? (2) What is the geomorphic effect of high-magnitude floods? (3) What does the sedimentary record tell us about river floods and the future of rivers?
BIO
Piret Plink-Bjorklund is Professor at Colorado School of Mines. Her research integrates lessons from the preserved sedimentary record with insights from modern process and experimental studies, with the aim to improve our ability to interpret the sedimentary record in an unbiased way, and to integrate the deep-time perspective of non-stationarity into geomorphology and climate research.
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