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Knickpoint formation, rapid propagation, and landscape response following coastal cliff retreat at the last interglacial sea-level highstand: Kaua‘i, Hawai‘i

Mackey, Benjamin H. and Scheingross, Joel S. and Lamb, Michael P. and Farley, Kenneth A. (2014) Knickpoint formation, rapid propagation, and landscape response following coastal cliff retreat at the last interglacial sea-level highstand: Kaua‘i, Hawai‘i. Geological Society of America Bulletin, 126 (7-8). pp. 925-942. ISSN 0016-7606. https://resolver.caltech.edu/CaltechAUTHORS:20140926-092926280

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Abstract

Upstream knickpoint propagation is an important mechanism for channel incision, and it communicates changes in climate, sea level, and tectonics throughout a landscape. Few studies have directly measured the long-term rate of knickpoint retreat, however, and the mechanisms for knickpoint initiation are debated. Here, we use cosmogenic ^3He exposure dating to document the retreat rate of a waterfall in Ka’ula’ula Valley, Kaua‘i, Hawai‘i, an often-used site for knickpoint-erosion modeling. Cosmogenic exposure ages of abandoned surfaces are oldest near the coast (120 ka) and systematically decrease with upstream distance toward the waterfall (<10 ka), suggesting that the waterfall migrated nearly 4 km over the past 120 k.y. at an average rate of 33 mm/yr. Upstream of the knickpoint, cosmogenic nuclide concentrations in the channel are approximately uniform and indicate steady-state vertical erosion at a rate of ∼0.03 mm/yr. Field observations and topographic analysis suggest that waterfall retreat is dominated by block toppling, with sediment transport below the waterfall actively occurring by debris flows. Knickpoint initiation was previously attributed to a submarine landslide ca. 4 Ma; however, our dating results, bathymetric analysis, and landscape-evolution modeling support knickpoint generation by wave-induced sea-cliff erosion during the last interglacial sea-level highstand ca. 120–130 ka. We illustrate that knickpoint generation during sea-level highstands, as opposed to the typical case of sea-level fall, is an important relief-generating mechanism on stable or subsiding steep coasts, and likely drives transient pulses of significant sediment flux.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1130/B30930.1 DOIArticle
http://gsabulletin.gsapubs.org/content/126/7-8/925PublisherArticle
http://bulletin.geoscienceworld.org/content/126/7-8/925PublisherArticle
ORCID:
AuthorORCID
Scheingross, Joel S.0000-0002-7220-8084
Lamb, Michael P.0000-0002-5701-0504
Farley, Kenneth A.0000-0002-7846-7546
Additional Information:© 2014 Geological Society of America. Received 22 May 2013. Revision received 19 November 2013. Accepted 31 December 2013. First published online March 6, 2014. This study was funded by the National Science Foundation (NSF) grants EAR-1204375 and EAR- 1147381 to Lamb. Light detection and ranging (LiDAR ) data were collected by the NSF National Center for Airborne Laser Mapping with a seed grant to Mathieu Lapotre. We thank Will Amidon and Lindsey Hedges for help in processing the cosmogenic ^3He samples. We had discussions with and field support from Taylor Perron, Ken Ferrier, Sujoy Mukhopadhyay, Matt Rosener, and Chuck Blay. Thorough reviews from Ken Ferrier, Kelin Whipple, Joel Johnson, an anonymous reviewer, and GSA Bulletin associate editor Anne Jefferson greatly improved this manuscript.
Funders:
Funding AgencyGrant Number
NSFEAR-1204375
NSFEAR-1147381
Issue or Number:7-8
Record Number:CaltechAUTHORS:20140926-092926280
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20140926-092926280
Official Citation:Benjamin H. Mackey, Joel S. Scheingross, Michael P. Lamb, and Kenneth A. Farley Knickpoint formation, rapid propagation, and landscape response following coastal cliff retreat at the last interglacial sea-level highstand: Kaua‘i, Hawai‘i Geological Society of America Bulletin, July 2014, v. 126, p. 925-942, First published on March 6, 2014, doi:10.1130/B30930.1
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50060
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:09 Oct 2014 22:45
Last Modified:09 Mar 2020 13:19

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