Analysis of Depositional Processes After the Columbia River Basalt Flows, Early Ellensburg Formation, Bettas Road, Ellensburg WA
Document Type
Oral Presentation
Campus where you would like to present
SURC Ballroom B/C/D
Start Date
21-5-2015
End Date
21-5-2015
Keywords
Columbia River Basalt, Ellensburg Formation, Environmental Evolution
Abstract
The Columbia River Basalt (CRB) flows ~15 million years ago flattened the topography of central Washington and altered the environments of existing river systems. The goal of our project is to understand how the local fluvial system responded to the CRB flows and eventually evolved into the environment we live in today by analyzing the laterally extensive outcrop at Bettas Road, which is an excellent example of sediment deposition immediately after a flood basalt event. Via hand sample and thin section analysis as well as published CRB flow maps, we confirmed that the base layer of the outcrop was of the Grande Ronde CRB flow, which indicates that the sediments deposited directly atop the basalt are the earliest of the Ellensburg Formation. We hypothesized that the first sediments deposited after the basalt would be fine-grained due to the unchannelized nature of the flattened topography, and that volcanic debris flows would dominantly be fine-grained and hyper-concentrated. We further predicted that, as rivers developed channels, the grain size would become larger and the volcanic debris flows would be dominantly coarser-grained lahars. To test these hypotheses, we mapped the 930 meter long outcrop, identified sedimentary facies, and performed grain-size analyses using a point-count method as well as sieves and a Mastersizer. Our results indicate that the grain size of both the fluvial and volcanic sediments generally coarsened upwards, as the fluvial system was not able to transport coarse-grained sediment immediately after the CRB flows but gradually evolved to transport larger material via mature channels.
Recommended Citation
Bennett, Kassia; Rogers, Sarah; and Beatty, Kimberly, "Analysis of Depositional Processes After the Columbia River Basalt Flows, Early Ellensburg Formation, Bettas Road, Ellensburg WA" (2015). Symposium Of University Research and Creative Expression (SOURCE). 13.
https://digitalcommons.cwu.edu/source/2015/posters/13
Poster Number
7
Department/Program
Geological Sciences
Additional Mentoring Department
Geological Sciences
Analysis of Depositional Processes After the Columbia River Basalt Flows, Early Ellensburg Formation, Bettas Road, Ellensburg WA
SURC Ballroom B/C/D
The Columbia River Basalt (CRB) flows ~15 million years ago flattened the topography of central Washington and altered the environments of existing river systems. The goal of our project is to understand how the local fluvial system responded to the CRB flows and eventually evolved into the environment we live in today by analyzing the laterally extensive outcrop at Bettas Road, which is an excellent example of sediment deposition immediately after a flood basalt event. Via hand sample and thin section analysis as well as published CRB flow maps, we confirmed that the base layer of the outcrop was of the Grande Ronde CRB flow, which indicates that the sediments deposited directly atop the basalt are the earliest of the Ellensburg Formation. We hypothesized that the first sediments deposited after the basalt would be fine-grained due to the unchannelized nature of the flattened topography, and that volcanic debris flows would dominantly be fine-grained and hyper-concentrated. We further predicted that, as rivers developed channels, the grain size would become larger and the volcanic debris flows would be dominantly coarser-grained lahars. To test these hypotheses, we mapped the 930 meter long outcrop, identified sedimentary facies, and performed grain-size analyses using a point-count method as well as sieves and a Mastersizer. Our results indicate that the grain size of both the fluvial and volcanic sediments generally coarsened upwards, as the fluvial system was not able to transport coarse-grained sediment immediately after the CRB flows but gradually evolved to transport larger material via mature channels.
Faculty Mentor(s)
Breanyn MacInnes