Post-Glacial Drainage Changes in the Darnley Bay Area, N. W. T., Canada

POST-GLACIAL DRAINAGE CHANGES IN THE DARNLEY BAY AREA, N. W. T. , CANADA* J. Ross Mackay University of British Columbia Darnley Bay is north of Great Bear Lake and midway between the Mackenzie and Coppermine Rivers which flow north into the Arctic Ocean. The three rivers which drain the area, namely the Brock, Hornaday , and Horton Rivers, are inaccurately shown on the latest 8 mile topographic sheet which was published in 1945, but a new and accurate map prepared from aerial photographs will shortly be available. Darnley Bay was discovered by Dr. John Richardson in 1826 but part of the inland area is still largely unknown. The mouth of the Horton River was discovered by Richardson and the river itself explored by Vilhjalmur Stefansson and Rudolph Anderson in 1909-12. ^ A, J. Stone, an American naturalist collecting for the American Museum of Natural History, discovered the Hornaday River in 1898. Until recent years the large size of the Hornaday River was unsuspected and it was considered to be a small stream rising from a lake 10 miles south of Darnley Bay, when in reality the river is about 200 miles long and the lake does not exist. The southern party of the 1913-18 Canadian Arctic Expedition explored the Brock River for 23 miles from its mouth. ^ Air photographs show it to be some 80 miles in length. The purpose of this paper is to discuss some of the post-glacial drainage changes which have occurred in the drainage basins of the Brock, Hornaday and Horton Rivers in the Darnley Bay area. Field work was done in the summer of 1951 and liberal use has been made of photo interpretation in extending the study to include a larger area. General Description The Darnley Bay region is in the barren grounds or tundra beyond the tree limit which lies close to the Horton River. Permanently frozen ground or permafrost is usually within five feet of the surface, except in areas of coarse granular materials. The area straddles the western boundary of the Canadian Shield which is shown on present geologic maps as reaching the coast at the southern end of Darnley Bay just east of the mouth of Brock River. In reality, the boundary should be shifted to the northeast because there is an area of Tertiary (?) sediments which are exposed northeast of Brock River and outcrop in an area of over 100 square miles. 5 The entire region was glaciated, and morainic material blankets most of the bedrock within 30 to 40 miles of Darnley Bay (excluding Parry Peninsula) but large areas of bedrock are exposed at the surface farther inland. Evidences for two directions of ice movement approximately at ?Based on field investigations carried out for the Geographical Branch, Department of Mines and Technical Surveys, Ottowa, with whose permission this paper is published. Thanks are due to Keith Fraser for his assistance in the field. 18 Yearbook of the Association Vol. 15 CAPE PARRY MILES Figure 1. Map of Darnley Bay area showing glacial lineatlon in ground moraine and bedrock with inset map to show general location 1953 of Pacific Coast Geographers 19 ,CAPE PARRY FRANKLIN BAY DARNLEY BAY CHANNEL A IIIBIIIIH.Î*·M >» MILES Figure 2. Map showing the principal post-glacial drainage channels. Dashed boundaries have been used to delimit drainage channels about which there is some uncertainty. 20Yearbook of the AssociationVol. 15 right angles to each other occur in the terrain. A general east-west trend is apparent across Parry Peninsula changing to a northeastsouthwest trend on the east side of Darnley Bay. This movement coincides with that of no known ice center. The other principal direction is found south and southeast of Darnley Bay where the ice moved from south to north, with a westerly component. This direction is a continuation of the projected trend from the Great Bear Lake area. Poet-Glacial Stream Capture As déglaciation progressed, the streams followed in general the regional slope of the land and drainage was in a chaotic state. It is possible to reconstruct much of the early drainage pattern from the evidences given by large, dry, abandoned valleys and also by misfit streams. The former drainage channels...