Did rock avalanche deposits modulate the late Holocene advance of Tiedemann Glacier, southern Coast Mountains, British Columbia, Canada?

- The advance of Tiedemann Glacier at 2.7 ka was anomalously large.
- Tiedemann Glacier advanced multiple times during the last 6000 years.
- Sudden input of rock avalanche debris to the glacier could explain its odd behavior.
- We develop and test a coupled ice dynamics debris advection model to test our hypothesis.

Most glaciers in western North America with reliable age control achieved their maximum Holocene extents during final advances of the Little Ice Age. Tiedemann Glacier, a large alpine glacier in western Canada, is an enigma because the glacier constructed lateral moraines that are up to 90 m higher, and extend 1.8 km farther downvalley, than those constructed during the Little Ice Age. Our data show that the activity of the glacier is more complex than originally documented and that the glacier advanced many times during the past six thousand years. Surface exposure dating and radiocarbon ages of stumps beneath till demonstrate that the glacier achieved its maximum Holocene extent at about 2.7 ka. We hypothesize that one or more rock avalanches delivered surface debris to the glacier and caused the 2.7 ka glacier advance to be much larger than can be explained by climate forcing. To test our hypothesis, we developed and used a surface debris advection routine coupled to an ice dynamics model. Our results show that even a moderately sized rock avalanche (10×106m3) delivered to the top of the ablation zone could cause the glacier to thicken and advance far beyond its Little Ice Age limit.