Indonesian Coastal Imbricated Boulders: Tsunami Indicator or Storm Wave Deposit? Measurement of non-Tsunami Boulder Motion Using UAVs and Structure from Motion Photogrammetry

Authors: Michael Bunds*, Utah Valley University, Alexander Uribe, Department of Earth Science, Utah Valley University, Orem, UT, USA, Daniel Horns, Department of Earth Science, Utah Valley University, Orem, UT, USA, Jeremy Andreini, Department of Earth Science, Utah Valley University, Orem, UT, USA, Ronald Harris, Department of Geological Sciences, Brigham Young University, Provo, UT, USA
Topics: Hazards, Risks, and Disasters, Pacific Rim, Remote Sensing
Keywords: Indonesia, UAV, Structure from Motion, tsunami, photogrammetry
Session Type: Poster
Day: 4/13/2018
Start / End Time: 1:20 PM / 3:00 PM
Room: Napoleon Foyer/Common St. Corridor, Sheraton, 3rd Floor
Presentation File: No File Uploaded

We generated three digital elevation models (DEMs) over a one-year period to measure boulder motion from wind-driven waves to assess whether a deposit of ~650 poorly boulders on the coastline of south Java, Indonesia (-8.241, 110.985), may have been formed by non-tsunami waves. The DEMs were created from photographs taken with unmanned aerial systems (UASs) and processed with structure-from-motion (SfM) methods. The first two DEMs were made from photographs taken with a DJI Phantom 2 equipped with a 24.3Mpixel Sony A5100 camera on 7/31/2016 and 8/2/2016, immediately before and after a 4.2m swell event synchronous with a +2.5m spring tide. The third DEM was made from photographs taken on 7/12/2017 with a DJI Phantom 4 Pro. All DEMs were georeferenced with real-time or post-processed-kinetic GPS measurement of ground control points (GCPs) using a local base. The same fixed GCPs were used for both 2016 DEMs. Raster-math differencing of the DEMs reveals boulder motion and other geomorphic changes. During the 2016 swell event, approximately 20 boulders up to 2m in length moved up to 5.6m. Between 2016 and 2017, approximately 300 boulders, average length 1.6m, moved 10cm to 30m. In addition, some boulders flipped 180-degrees about sub-horizontal axes, and at least one boulder ~1m in length was removed from the site. These results show that non-tsunami waves significantly affect the deposit, that boulder transport models that incorporate only sliding and ignore rolling do not appropriately account for natural boulder motion, and that wind-driven waves could have formed the studied deposit.

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