Landforms of British Columbia 1976 - Department of Geography
Landforms of British Columbia 1976 - Department of Geography Landforms of British Columbia 1976 - Department of Geography
trolled by a branch fault, extends from Beresford Inlet to Tahmkwan island, a distance of 20 miles. On southern Vancouver Island there are a number of prominent lineaments. Two outstanding ones have an almost east-west trend. One, the Lee& River lineament (17) (see photo B.C. 1533:14), extends from the west coast at the mouth of Loss Creek for 35 miles to the mouth of Goldstream Creek. It follows the valleys of Loss Creek, Wye Creek, Bear Creek, Leech River, Old Wolf Creek, and Goldstream Creek, all of which are along the trace of the Leech River fault. The San Juan lineament (18) extends from Port Renfrew in an easterly direction for about 35 miles to the west arm of Shawnigan Lake. It follows the valleys of San Juan River, Clapp Creek, and Koksilah River, which are eroded along the trace of the San Juan fault. The Cowichan Valley, occupied by Cowichan River and Lake and by Nitinat River tributaries, is a curving fault-controlled lineament (19) with a northwesterly trend and a length of 40 miles. It is only one of a number of fault-controlled valleys with that general trend. Liieaments are extremely well displayed in maps and aerial photographs of the He&e (see Plate VIA) and Georgia Lowlands and of the fiord section of the Kitimat and Pacific Ranges, by the alignment of river valleys, waterways, lakes, ridges, and various warps or depressions. Of the great many lineaments displayed along the coastline, the Owikeno lineament (20) deserves mention. It is well shown on N.T.S. Sheet 92~ and in Plate XLVIII by the easterly trending alignment of Elizabeth Lake, Hardy Inlet, Owikeno Lake, and Machmell River for a length of more than 50 miles. The photograph shows major joints parallel to the Owikeno lineament crossing a northerly trending line&on which is the topographic expression of bedding in a roof pendant. Grenville Channel lineament (21), 65 miles long, is the longest of the north- westerly trending lineaments on the coast. There are northeasterly trending line- aments such as that of Portland Inlet and Observatory Inlet, 60 miles long, as well as northerly ones such as those of Douglas Channel, Laredo Inlet, and Fitz- hugh Sound. Peacock’s study of the fiords of the British Columbia coast indicates that they are structurally controlled by “axes of folds, the strikes and contacts of geological formations, and the directions of joints, goes, faults, dikes, mineral veins, and shear zones of the surrounding country.“* “Severe folding has affected the pre-batholithic rocks [whose] prin- cipal fold-axes trend in general northwestward with considerable local sinuosity in sympathy with the composite crescentic plan of the coastland. This trend is the same as that of the longitudinal (concentric) component of the concordant pattern [see p, 1151. A study of the available reconnaissance geological maps of the coastland reveals many fiord features strictly following the strike of the local formations and the linear contacts between different formations. Grenville Chan- nel, an unusually straight and narrow passage (lat. 53” 30’), marks a boundary between granitoid and slaty rocks along 30 miles of its typical longitudinal COU*Se.“* “ All four principal fiord trends are represented by fracture lines; the longitudinal [northwesterly] and transverse [northeasterly] components of the concordant pattern are most strongly repreSented; the meridional [northerly] component of the discordant pattern is less commonly repeated; the east-west * Peacock, M.i\.. Gd. sot., Am., Bull. “Ol. 46, 193% pp. 656. 657, 658, 660. 124
component of the discordant pattern is feebly represented except in the vicinity of latitude 5 1”) where it is the most prominent one.“* That direction has been emphasized by erosion of glacial ice moving westward from the high gathering grounds of the Silverthrone, Waddington, and Homathko massifs. “There is, thus, an impressive correspondence of the pattern of the valley and fiord systems of the coastland to the underlying pattern of folds, fractures, and faults.“* The Denali fault is a structure which has served to localize a major lineament of northwestern North America. From Alaska the Den&’ lineament (22) extends through the Yukon as the Shakwak Valley as far as Dezadeash Lake and thence it turns southeastward up the Tatshenshini River. In British Columbia it follows the valley of Blanchard River and Mansfield Creek and thence down the K&all River to the head of Chilkat Inlet. From there the lineament is submerged beneath Lynn Canal and Chatham Strait past Dixon Entrance and thence along a sub- marine valley immediately offshore from the west coast of the Queen Charlotte 1slands.t The Denali fault is interpreted as being a major zone of faulting which is con- tinuous though multibranched. Movement along the fault has been intermittent over a long period of time and has continued through to the present. Recent earthquakes in the vicinity of Anchorage, Yakutat Bay, and the Queen Charlotte Islands resulted from movements along it. It is suggested by St. Amandt that the strike-slip movement on the fault is about 150 miles, but other evidences has been presented to indicate that the amount of movement may not be quite so great and that some of it may be high angle thrusting. [References: Wilson, J. T., “An Approach to the Structure of the Canadian Shield,” Trans., Am. Geoph. Union, Vol. 29, 1948, pp. 691-726; Gross, W. H., “A Statistical Study of Topographic Linears and Bedrock Structures,” Proc., Geol. Ass. Can., Vol. 4, 1951, pp. 77-88; Twenhofel, W. S., and Sainsbury, C. L., “ Fault Patterns in Southeastern Alaska,” Gad. Sm., Am., Bull. Vol. 69, 1958, pp. 1431-1442.1 [Photographs: B.C. 468: 83; B.C. 469: 59, 96; B.C. 489: 60; B.C. 498: 40; B.C.501:48, 111; B.C.502:72; B.C.566:55; B.C. 589:18; B.C. 975:88; B.C. 1207:85; B.C. 1231:73, 80; B.C. 1404:21.] 125
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component <strong>of</strong> the discordant pattern is feebly represented except in the vicinity <strong>of</strong><br />
latitude 5 1”) where it is the most prominent one.“* That direction has been<br />
emphasized by erosion <strong>of</strong> glacial ice moving westward from the high gathering<br />
grounds <strong>of</strong> the Silverthrone, Waddington, and Homathko massifs.<br />
“There is, thus, an impressive correspondence <strong>of</strong> the pattern <strong>of</strong> the valley<br />
and fiord systems <strong>of</strong> the coastland to the underlying pattern <strong>of</strong> folds, fractures,<br />
and faults.“*<br />
The Denali fault is a structure which has served to localize a major lineament<br />
<strong>of</strong> northwestern North America. From Alaska the Den&’ lineament (22) extends<br />
through the Yukon as the Shakwak Valley as far as Dezadeash Lake and thence it<br />
turns southeastward up the Tatshenshini River. In <strong>British</strong> <strong>Columbia</strong> it follows<br />
the valley <strong>of</strong> Blanchard River and Mansfield Creek and thence down the K&all<br />
River to the head <strong>of</strong> Chilkat Inlet. From there the lineament is submerged beneath<br />
Lynn Canal and Chatham Strait past Dixon Entrance and thence along a sub-<br />
marine valley immediately <strong>of</strong>fshore from the west coast <strong>of</strong> the Queen Charlotte<br />
1slands.t<br />
The Denali fault is interpreted as being a major zone <strong>of</strong> faulting which is con-<br />
tinuous though multibranched. Movement along the fault has been intermittent<br />
over a long period <strong>of</strong> time and has continued through to the present. Recent<br />
earthquakes in the vicinity <strong>of</strong> Anchorage, Yakutat Bay, and the Queen Charlotte<br />
Islands resulted from movements along it. It is suggested by St. Amandt that the<br />
strike-slip movement on the fault is about 150 miles, but other evidences has been<br />
presented to indicate that the amount <strong>of</strong> movement may not be quite so great and<br />
that some <strong>of</strong> it may be high angle thrusting.<br />
[References: Wilson, J. T., “An Approach to the Structure <strong>of</strong> the Canadian<br />
Shield,” Trans., Am. Geoph. Union, Vol. 29, 1948, pp. 691-726; Gross, W. H.,<br />
“A Statistical Study <strong>of</strong> Topographic Linears and Bedrock Structures,” Proc., Geol.<br />
Ass. Can., Vol. 4, 1951, pp. 77-88; Twenh<strong>of</strong>el, W. S., and Sainsbury, C. L.,<br />
“ Fault Patterns in Southeastern Alaska,” Gad. Sm., Am., Bull. Vol. 69, 1958,<br />
pp. 1431-1442.1<br />
[Photographs: B.C. 468: 83; B.C. 469: 59, 96; B.C. 489: 60; B.C. 498: 40;<br />
B.C.501:48, 111; B.C.502:72; B.C.566:55; B.C. 589:18; B.C. 975:88; B.C.<br />
1207:85; B.C. 1231:73, 80; B.C. 1404:21.]<br />
125
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