Holocene Periods of Aggradation and Incision, Hanson Creek, Washington

<p>The causes and timing of cycles of aggradation and incision in the Hanson Creek drainage in central Washington provide insight into changes in channel morphology and paleoenvironment within the region over the last 8000 years. Stratigraphically and spatially coincident archaeological evidence reveals information related to human occupation during the latter half of the epoch. Using LiDAR imagery and field surveys, recent processes such as degree of modern channel incision, accumulation of valley floor sediment, channel morphology and gradient were evaluated. The spatial distribution of these channel characteristics was assessed in relation to proximal landforms such as colluvial deposits, basalt outcrops, and bedrock anticlinal ridges. Sixteen stratigraphic profiles in the arroyo walls were used to delineate and correlate past depositional episodes based on sediment characteristics. Basal ages of the earliest documented depositional period were constrained using geochemical analysis of tephra beds. Intermediate dates were obtained from ¹⁴C analysis of <em>in situ</em> charcoal. The results reveal an aggrading fluvial system that entrained and transported silt to cobble sized sediment from a minimum age of 7680-7580 BP prior to the historic arroyo incision event, which most likely occurred between AD 1878 and AD 1954. The cause of the incision is likely a combination of factors, including thick accumulations of easily erodible sediment in reaches of shallow valley gradient and intervening steep gradients. Although the event that triggered the incision is unknown, similar arroyos in the western U.S. have been initiated by high magnitude floods that incised initial knickpoints, subsequently lowering base level.</p>

Name thesis:degree_name

Master of Science (MS)

Discipline thesis:degree_discipline

Geological Sciences

Year dc:date.available

2019

Author dc:creator

• Windingstad, Levi Earl

Contributors dc:contributor

• Lisa Ely
• Breanyn MacInnes
• Steven Hackenberger

• Arroyo
• Bishop's Hollow
• Yakima Training Center
• Archaeological Anthropology
• Geology
• Geomorphology
• Sedimentology

Repository record dc:identifier

https://digitalcommons.cwu.edu/etd/1336

OAI identifier oai:identifier

oai:digitalcommons.cwu.edu:etd-2337