The avalanches that followed the canyons of Annie and Sun creeks probably came to rest in the vicinity of Fort Klamath, having moved a distance of about 15 miles. Possibly they reached the edge of Upper Klamath Lake, which was then slightly higher than now and extended farther north. The flows that passed through Kerr Notch into the valleys of Sand and Wheeler creeks filled them to a depth of 250 feet in places. So rapidly did they move that even 13 miles from the source, after they had debouched onto the plateau at the foot of Mount Mazama, they rushed up the onset slope of Boundary Butte to a height of 200 feet.
On the east side of Mount Mazama there were no large glacial troughs; nevertheless the flows had not passed far beyond the present rim of the caldera before they were deflected into the narrow valleys of Scott and Bear creeks. These they followed down to the plateau, where they reunited and continued eastward for 10 miles or more to the edge of the Klamath Marsh. The more voluminous flows that raced down the northeast slope of the volcano along Desert Creek, combining with those which crossed the Pumice Desert and turned eastward through the depression between Timber Crater and Mount Thielsen, spread as far as Chemult, a distance of 25 miles, though the last 15 miles of their path lay across ground that was almost flat.
Part of the flow which crossed the Pumice Desert continued northward into Diamond Lake. How it crossed the lake is not: clear, but that it did so is apparent, for thick deposits of unstratified pumice may be found in the upper stretches of both Clearwater and North Umpqua rivers. Another branch of the same flow swerved westward into the headwaters of the Rogue River to augment those that swept down the northwest slope of the volcano. The latter did not begin to deposit much of their load until they reached the head of National Creek, between 8 and 9 miles from the vent.
Much of the pumice which poured down National, Bybee, Copeland, Castle, and Union creeks united to form a single flow in the valley of the Rogue, and the composite mass rushed another 20 miles almost to the site of the present village of McLeod.
Fig. 24. Size distribution of samples of pumice flow (lump pumice). Fraction less than 1/8 mm. omitted. (After B. N. Moore, Journal of Geology, vol. 42, p. 365, 1934. Numbers in parentheses refer to Moore’s samples.) |
As compared with the deposits left by glowing avalanches around other volcanoes, those of Mount Mazama are unusually large. Even in a straight line, the snout of the Rogue River flow is 35 miles distant from the source; the actual distance traveled must have been more than 40 miles. By contrast, the great “sand flow” in the Valley of Ten Thousand Smokes was 11.5 miles long, and few of the pumice flows and glowing avalanches of Pelée and Komagatake spread more than 4 miles from their source. The Crater Lake deposits compare, rather, with the widespread tuff sheets which encircle the caldera of Aso, Japan, or with those that form the extensive plateaus around the collapse depressions of Lakes Ranau and Toba in Sumatra and Lake Taupo in New Zealand.
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