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SDAG Joint Meeting with SCGS - VIRTUAL
Monday - June 7, 2021

Location: Your house, in front of your computer

6:00pm - 7:00pm get logged in, social hour via web platform
7:00pm - Meeting begins

Join Zoom meeting from PC, Mac, Linux, iOS or Android:
Meeting ID: 631 527 5954
Passcode: 030187

happy hour

Menu: What's in your fridge?

Cost: Free - BYO food and drinks.
If you are a current SDAG member and are not getting e-mail announcements,
make sure the SDAG secretary has your correct e-mail address.

7:00pm -

"Long term coastal cliff retreat in Del Mar, CA revealed from shore platform 10Be concentrations and numerical modeling"

Speaker: Travis Clow - PhD Candidate at Stanford University

Long term coastal cliff retreat in Del Mar, CA revealed from shore platform 10Be concentrations and numerical modeling
T. Clow, J.K. Willenbring, H. Matsumoto, A. Young, A. Hidy

Eroding coasts make up the majority of the coastlines on Earth, including the west coast of the United States, and host critical infrastructure like roads, railways, and residential structures. The precarious siting of infrastructure is particularly true for Del Mar, California, where a major railway between Los Angeles and San Diego sits within just a few meters of a cliff edge that is closely backed by dense housing subdivisions. Coastal cliff retreat presents a danger to these communities that is potentially amplified under rising sea level conditions, among other factors, yet constraints on retreat rates are most often limited to those derived from historical imagn ery and maps dating back 10-100 years. These modern retreat rates are then used, in conjunction with multi- model ensembles, for forecasting cliff retreat over the next 50-100 years in order to gauge future impacts to coastal communities. Managers and policymakers make decisions for mitigation efforts based on these results, however they may not capture the full picture of cliff retreat, and the factors that influence it, over time. While nearly all of the existing forecasting models explicitly account for projected sea level rise, the majority of them ignore other factors (e.g. subtidal and subaerial weathering) that may also play a large role.

A recently developed combination of in situ-produced cosmogenic 10Be surface exposure dating in conjunction with a new numerical model of shore platform profile development that takes into account sea level rise, intertidal weathering, and wave attack on cliff retreat provides quantification of cliff retreat histories over hundreds to thousands of years via cliff-normal 10Be sample transects. Here, we use a shore-perpendicular transect of cosmogenic 10Be concentrations from the surface of a sandy claystone shore platform exposed along a narrow and sandy beach backed by a near vertical ~20-meter-tall cliff in Del Mar, California to present a long-term cliff retreat rate of 5.5 - 8 cm a-1 over the last two millennia for this site. This is the first long term cliff retreat rate for any coast in North America determined by this new methodology. Existing decadal retreat rates at and proximal to this site range from 5-20 cm a-1, suggesting that cliff retreat here may be accelerating towards the present. Preliminary modeling results suggest that uplift-corrected sea level rise in Southern California, which remained constant during the late Holocene (0.8 mm a-1) but doubled in the last century, cannot alone explain this potential increase, as modeled platform geometries and associated development rates show a dependence on the imposed weathering rate as well as wave erosion efficacy. Recent investigation into the relative influence of weathering and wave attack on observed cliff retreat at this same location also shows a roughly equal contribution for both drivers. We further explore this and other potential drivers (e.g. land use change) for this potential increase, and speculate on the implications of these results for future cliff retreat forecasting efforts.

Travis Clow is currently a PhD Candidate at Stanford University working with Dr. Jane Willenbring on resolving rates and dates of landscape evolution in North and Central America using cosmogenic nuclides. He received his master's and bachelor's degrees at the University of Texas at Austin in 2017 and 2014, respectively. His main research interests involve unraveling the interplay of climate and tectonics as drivers of Quaternary geomorphological landscape change from coasts to mountain belts, as well as active tectonics and critical zone science. Outside of the lab and field, Travis spends his time hiking, skateboarding, and relaxing anywhere with a nice view.

  • Outstanding Teaching Assistant Award, Scripps Institution of Oceanography / UC San Diego (Spring 2019)
  • Early-Career Graduate Best Poster Award, Runner-up, The University of Texas at Austin, Jackson School of Geosciences (Spring 2016)
  • Undergraduate Merit Based Scholarship, The University of Texas at Austin, Jackson School of Geosciences (Spring 2013 - Fall 2014)
  • University Honors, The University of Texas at Austin (Fall 2012, Spring 2014)
  • President's List, The University of Texas at San Antonio (Fall 2009 - Spring 2010)

Upcoming SDAG meetings - 2021

June 7: - Next meeting will be a joint meeting with South Coast Geological Society. For this reason, it will be held on MONDAY JUNE 7th in lieu of our usual Wednesday.

Meetings are usually scheduled for the 3rd Wednesday evening of the month. Meeting information on this website is normally updated the second week of the month.

Recordings of past meetings

5//2021: Hans Janzon "Nuclear Waste Disposal in Rock: Sweden and the US"
Passcode: AQpMR@4#

4/21/2021: EERI Speakers: 1) Prof. Thomas Rockwell (San Diego State University), 2) Timothy Dawson (California Geological Survey), 3) Michael DeFrisco (California Geological Survey), 4) Discussion Q&A. Moderator: Dr. Jorge Meneses

3/17/2021: Barry Keller "Sediment Transport in the San Francisco Bay Estuarine System"
Passcode: 5+Y5m?h@

2/17/2021: Dr. Norrie Robbins "Origin of Our Redbeds Pigmentation by Chembiotic Oxidation of Detrital Magnetite in Red Brown Pleistocene Terrace Sandstones, San Diego, CA."
Passcode: ^DK2UW0=

1/20/2021: W. Paul Burgess, M.S., P.G. California Geological Survey "Shallow landslide and debris flow activity in San Diego County, early April, 2020"
Note: ZOOM speaker's presentation begins at time 1:44:00.

12/16/2020: Dr. Tom Demere of the SDNHM "Suprise Talk!!."
Passcode: b.Wh7f&&
Note: ZOOM speaker's presentation begins at time 1:10:00.

If you have any information, announcements, ads or suggestions for an upcoming newsletter, please submit it to 2021 SDAG Secretary. Any news regarding upcoming events that may be of interest to the Association or news of your business can be submitted. The submittal deadline for the next SDAG newsletter is the last Friday of the month.
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