Reading the 10,000 year sediment record from lake sediments

Researchers from the University of British Columbia and Simon Fraser University have teamed up with Geometrics to develop a composite picture of sediment accumulation at the bottom of a large (12 km²) glacial lake in the Cascades Mountains. The project aims to develop a long term record of sediment transfer in the valley, in order to understand how the long process of evacuation of large stores of glacial sediment from the Cordilleran ice sheet has conditioned hillslope and river behavior.

The Chilliwack Valley is located in the lower mainland of British Columbia, roughly 100 km east of Vancouver. The drainage basin straddles the US border, with much of the southern (U.S.) portion residing in the Cascades National Park. The valley shows abundant evidence of prior occupation by the ice sheets of the Fraser Glaciation, with its U-shaped profile, hanging valleys, alluvial terraces, lacustrine beds, and blankets of morainal material.

Chilliwack Lake began as a body of meltwater from the valley glacier, caught between the glacier and its recessional moraine. The lake has persisted over the Holocene period, long after the disappearance of the glacier. The lake is an effective sediment trap for sediments delivered from the mountainous catchments in the upper valley. The accumulation of sediments in this deep (100m+) lake provides a continuous, integrated record of sediment accumulation over 10,000 years.

Signals from a Bubble Pulser source were collected using a[two eel hydrophone array. Twenty-four channels were output to the Geode unit. All of the apparatus was powered by a 1 kW generator. Real-time data acquisition was spooled to a laptop computer. The total system setup was compact and easily deployed, particularly in comparison with other 'state of the art' solutions such as the CHIRP system, which tended to threaten the stability of the vessel. A penetration of over 20m was achieved throughout much of the survey, and the resolution of the final output provided excellent detail of individual layers. See figure below.