Title

Eight Thousand Years of Sedimentation and Arroyo Formation, Hanson Creek, Yakima Training Center, Washington

Presenter Information

Levi Windingstad

Document Type

Oral Presentation

Location

SURC Ballroom B/C/D

Start Date

21-5-2015

End Date

21-5-2015

Keywords

Arroyo, Hanson Creek, Sedimentation

Abstract

The causes and timing of cycles of sedimentation in the Hanson Creek drainage in central Washington provide insight into changes in channel morphology and paleoenvironment within the region over the last 8,000 years. Using LiDAR imagery and field surveys, recent processes such as degree of modern channel incision, accumulation of valley floor sediment, and channel morphology and gradient were evaluated. The spatial distribution of these channel characteristics was assessed in relation to proximal land forms such as spring mounds, colluvial deposits, and basalt outcrops. 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 charcoal. Stratigraphic evidence suggests multiple transitions from an aggrading braided system to an expansive, fine-grained, alluvial step-pool sequence that aggraded a minimum of 3.5 m throughout the last 8,000 years. Low gradient, fine-grained, organic-rich, sediment suggests prolonged periods of saturation at three locations throughout the incised reach, adjacent to evidence of groundwater springs. The intervening reaches exhibit comparatively high gradients for unconsolidated alluvium. A single and unprecedented 9 m deep incision of a 1.8 km reach occurred around AD 1900. The timing and physical environmental conditions associated with Holocene sedimentation in the Hanson Creek watershed will supplement the minimal data available on arroyo formation in the northwestern United States, and allow a comparison with the timing of archaeological occupation sites adjacent to Hanson Creek.

Poster Number

10

Faculty Mentor(s)

Lisa Ely

Department/Program

Geological Sciences

Additional Mentoring Department

Geological Sciences

This document is currently not available here.

Share

COinS
 
May 21st, 8:30 AM May 21st, 11:00 AM

Eight Thousand Years of Sedimentation and Arroyo Formation, Hanson Creek, Yakima Training Center, Washington

SURC Ballroom B/C/D

The causes and timing of cycles of sedimentation in the Hanson Creek drainage in central Washington provide insight into changes in channel morphology and paleoenvironment within the region over the last 8,000 years. Using LiDAR imagery and field surveys, recent processes such as degree of modern channel incision, accumulation of valley floor sediment, and channel morphology and gradient were evaluated. The spatial distribution of these channel characteristics was assessed in relation to proximal land forms such as spring mounds, colluvial deposits, and basalt outcrops. 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 charcoal. Stratigraphic evidence suggests multiple transitions from an aggrading braided system to an expansive, fine-grained, alluvial step-pool sequence that aggraded a minimum of 3.5 m throughout the last 8,000 years. Low gradient, fine-grained, organic-rich, sediment suggests prolonged periods of saturation at three locations throughout the incised reach, adjacent to evidence of groundwater springs. The intervening reaches exhibit comparatively high gradients for unconsolidated alluvium. A single and unprecedented 9 m deep incision of a 1.8 km reach occurred around AD 1900. The timing and physical environmental conditions associated with Holocene sedimentation in the Hanson Creek watershed will supplement the minimal data available on arroyo formation in the northwestern United States, and allow a comparison with the timing of archaeological occupation sites adjacent to Hanson Creek.