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Graduation Term

2018

Degree Name

Master of Science (MS)

Committee Chair

Lisa Tranel

Abstract

Sandstone exposures in North-central Illinois are investigated using photogrammetric Structure-from-Motion (SfM) analyses to understand present day erosion rates following post-glacial canyon incision. Petrographic and rock strength analyses are also conducted in attempts to correlate trends between short-term erosion and rock characteristics. Retreat of Wisconsin glaciers (~19,000 years ago) caused outwash floods, resulting in canyons carved ~50-200m deep into the St. Peter Sandstone (Curry et. al, 2014). The St. Peter Sandstone is a weakly cemented, extremely friable quartz arenite, which allows for easy erosion. This study takes place in and around Starved Rock State Park, which is one of the most frequently visited natural attractions in Illinois. Due to the large number of visitors to the park and the sandstone properties, canyons are susceptible to human disturbance and natural erosion, mainly in the form of carvings. The focus of this study is to explore how quickly short-term, present day erosion is occurring in the park. Repeat SfM photographic data were collected from two study sites located in different canyons where canyon walls exhibit various carvings from human interaction. Data were gathered once per month for six months from each site, with 50-150 photographs taken at varying distances and angles from the canyon wall of focus. Densely collected photographs were uploaded to a computer program, Agisoft PhotoScan Pro, which was used to construct a 3D point cloud. Following creation, point clouds were imported into CloudCompare to calculate differences in rock faces between monthly visits at each site. Rock strength and petrographic data were collected at the two SfM sites and three additional sites. Rock strength analyses were conducted using an N-type Schmidt hammer. Petrographic thin sections were used to calculate porosity and cement content in rocks gathered at study sites.

Quantifying monthly changes allowed for comparison of differences in surface topography following erosion events. Results from the photogrammetric SfM analysis showed measurable change on a centimeter to millimeter scale between canyon faces at two locations over the course of six months. The majority of change occurred during the winter months, alluding to seasonal events including increased precipitation and meltwater flow following snowfall, in addition to human influence. Localized erosion found along a foot path in LaSalle canyon during more frequently visited fall months demonstrates the influence humans have on the park in such a short time span. Canyon locations exhibiting lower cement content and higher grain percentage values indicated more erosion occurring over the six-month time frame. Characteristics of the St. Peter sandstone, including rock strength, porosity, grain percentage, and cement content, are influential driving factors continually affecting erosion rates in this area.

Access Type

Thesis-ISU Access Only

DOI

http://doi.org/10.30707/ETD2018.Rutte.M

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