Asymmetric Stream Migration

There is a tendency for clear streams flowing in the east-west direction in central Alaska to migrate slowly northward in their valleys while clear streams that flow north-south tend to meander randomly about a central position. Thus, the ox-bow meanders tend to lie more on the south side while a stream bed moves northward. A local example is the Salcha River.

An early explanation for the curious meander of clear streams is related to the low sun angles that prevail in the north country. It has been suggested that the ground on the south side of a stream tends to be shadowed more than the north side. Therefore, the south banks can stay frozen longer in the spring and be more resistant to erosion during the seasonal flood stage.

Another explanation comes from knowledge of the behavior of the crust of our earth. There is evidence that the earth's crust under the North Pacific Ocean is thrusting northward against the North American continent with enough force to cause the region near the Alaska Range to slowly rise. This tips the Tanana Valley so that water tends to move to the north. The meandering of silt-laden streams, such as the Tanana River, is influenced by the source and deposition of the silt. Much of the Tanana's silt load comes from the glaciated mountains to the south and this also may force the riverbed northward.