GEOTOUR GUIDE - City of Kamloops

(sTop 4) red laKe road and Tranquille:
a vieW of The GroWinG delTa of
The Thompson river & shrinKinG Kamloops laKe
Are you ready to test your imagination? Geologists interpret that at one time, several thousand years ago, the city centre of
modern Kamloops sat on the shores of a larger Kamloops Lake. However, the North Thompson River acts as a great conveyor belt
carrying sand and silt. Over the years the river continued to dump its load of sediment at its delta where it flowed into Kamloops
Lake. Year after year, the lake shoreline moved westwards as the eastern end of the lake filled. This process continues today, with
the delta front migrating westwards about 13 metres each year. Geologists estimate that if the modern rate of advance continues,
Kamloops Lake will fill completely in 4000 years. Kamloops Lake will become Kamloops valley!
The legacy of this westward advance is a flat delta plain that extends from Kamloops to Kamloops Lake. The land is flat because
the sand and silt are deposited in the channel of the Thompson River or on the adjacent plain during spring floods. During these
floods, the delta plain is inundated with a slow-moving lake of muddy water that leaves behind a layer of sand and silt (just ask
anyone who has had their house flooded). This sand and silt is rich agricultural soil and much of the delta is farmland.
The drive up Red Lake Road past Tranquille to a roadside pullout at Stop 4a offers panoramic view of Kamloops Lake and the
Thompson River delta. The access road and walk along the Lake Trail at Tranquille (Stop 4b) provides close up views of the
delta lands, sand bars, and wetlands of the Thompson River delta. It also provides a look at the much smaller gravel delta of the
Tranquille River.
Figure 16. A winter time view of the mouth of the Thompson River where it enters Kamloops Lake, from the Red Lake Road near Stop 4a. This is the delta
of the Thompson River, built of sand and mud deposited by the Thompson River as its waters slow upon entering Kamloops Lake. Features in the photograph
are described from left to right: a cliff of volcanic rock; flat agricultural lands, forests, and wetlands on the delta plain of the Thompson River; broad sand bars
exposed in the channel of the Thompson River during the low water conditions typical of the winter period; forests and sewage lagoons (Stop 14) on the delta
plain south of the river; and the gullied southern slopes of the Thompson River valley. (Photo by R. Turner)
Figure 17. A view to the south and west across the Thompson River delta and estuary from the Cinnamon Ridge trail at Stop 2. The delta plain is the flat top
of a thick sequence of sand and silt deposited into Kamloops Lake by the Thompson River. The estuary is rich wetland habitat for wildlife and fish where river
waters mix with lake waters. The City of Kamloops compost facility (Stop 15) is the dark brown rectangle in the lower right. (Photo by R. Turner)
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