344 



L. MARTIN — ALASKAN EARTHQUAItES OP 1899 



northwest of it, and from them the Copper River flows southward, cross- 

 ing the Chugach Mountains and entering the Pacific about 200 miles west 

 of Yakutat Bay. The Alsek Eiver flows southward from the interior of 

 Alaska, entering the Pacific about 60 miles east of Yakutat Bay. The 

 White River and the Tanana, headwaters of the Yukon from the Saint 

 Elias and Wrangell Mountains, flow northward. 



TOPOGRAPHY AND GEOLOGY OF THE EARTHQUAKE ORIGIN^ 



The three topographic features near Yakutat, around which was the 

 earthquake origin, are : ( 1 ) the Yakutat foreland, a glacial coastal plain 

 less than 250 feet above sealevel; (2) the foothills, rising from 3,000 to 

 4,550 feet, and (3) the Saint Elias Range, 10,000 to 19,000 feet high. 

 Yakutat Bay, a fiord shaped like a bent arm, consists (figure 3) of (a) a 

 broad outer bay in the foreland; (b) Disenchantment Bay, a deep fiord 

 in the foothills and mountains, and (c) Russell Fiord, partly in the moun- 

 tains, partly in the foothills, and partly in the foreland. A piedmont ice- 

 sheet, the Malaspina glacier, covers the foreland on the west side of Yaku- 

 tat Bay, and there are extensive alpine glaciers entering the fiords and 

 mountain valleys and supplied from the snowfields, which cover everything 

 above 3,000 feet where slopes permit. The fiords are chiefly the work of 

 glacial erosion. 



The geology of this area of the earthquake origin includes rocks of at 

 least four different ages : ( 1 ) Paleozoic or older intrusive and metamor- 

 phic rocks; (2) the Yakutat group of sediments, perhaps Mesozoic; (3) 

 the Tertiary coal-bearing group, and (4) the Quaternary glacial and 

 terrestrial accumulations. The Quaternary formations cover the Yaku- 

 tat foreland and form valley deposits in the mountains. The Tertiary 

 includes an exceedingly small area at the base of the foothills west of 

 Yakutat Bay. The Yakutat group includes all the foothill region and 

 part of the mountains. A northwest to southeast line extending through 

 the northwest arm of Russell Fiord (figure 3) separates the Yakutat 

 group from the metamorphic and igneous older group of rocks. This 

 is an old fault-line, one of those along which renewed movement caused 

 the 1899 earthquakes, particularly that of September 10. The pros- 

 pectors who experienced these earthquakes from a camp near the junction 

 of Disenchantment Bay and Russell Fiord (figure 3) were, therefore, 

 right on a fault-line. Another old fault separates the Tertiary coal- 

 bearing group from the Yakutat group. A third old fault, inferred by 

 I. C. Russell in 1890, on the basis of topographic form,^ separates the 



^ Fully described in U. S. Geological Survey Professional Paper no. 64, 1909. 

 • National Geographic Magazine, vol. 3, 1891, p. 57. 



