Abstract
A 5.6-m-long lake sediment core from Bear Lake, Alaska, located 22 km southeast of Redoubt Volcano, contains 67 tephra layers deposited over the last 8750 cal yr, comprising 15% of the total thickness of recovered sediment. Using 12 AMS 14C ages, along with the 137Cs and 210Pb activities of recent sediment, we evaluated different models to determine the age-depth relation of the core, and to determine the age of each tephra deposit. The selected age model is based on a mixed-effect regression that was passed through the adjusted tephra-free depth of each dated layer. The estimated age uncertainty of the 67 tephras averages ±105 yr (95% confidence intervals). Tephra-fall frequency at Bear Lake was among the highest during the past 500 yr, with eight tephras deposited compared to an average of 3.7/500 yr over the last 8500 yr. Other periods of increased tephra fall occurred 2500-3500, 4500-5000, and 7000-7500 cal yr. Our record suggests that Bear Lake experienced extended periods (1000-2000 yr) of increased tephra fall separated by shorter periods (500-1000 yr) of apparent quiescence. The Bear Lake sediment core affords the most comprehensive tephrochronology from the base of the Redoubt Volcano to date, with an average tephra-fall frequency of one every 130 yr.
Original language | English (US) |
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Pages (from-to) | 56-67 |
Number of pages | 12 |
Journal | Quaternary Geochronology |
Volume | 3 |
Issue number | 1-2 |
DOIs | |
State | Published - Feb 2008 |
Keywords
- Alaska
- Cook inlet
- Redoubt volcano
- Tephra
- Tephra-fall frequency
- Tephrochronology
- Volcanic hazards
ASJC Scopus subject areas
- Geology
- Stratigraphy
- Earth and Planetary Sciences (miscellaneous)