National Geographic : 1911 Jun
RESEARCHES IN ALASKA 545 Since resting where one stood to take a pho Stograph the day before, or to find some H great tree, Ioo years old, prone on the Ground with the butt beneath the glacier, I where the day before the tree was up Sright with the ice just touching it or with Room to go between the glacier and tree. .Z The rate of movement in midglacier during the summer was not determined, ^ but it would not be improbable, judging H from the rate at the north margin and From rates at intervals across other gla Sciers that have been measured, that it Swas at least six times the rate in 1909, or S30 feet a day, and even more at times. S But the middle of the glacier did not Advance as far during the summer as the North margin did, and between June Io and August I it retreated 450 feet. From August ii to August 17 it re a treated 65 feet more. This retreat was B occurring while the north margin was i advancing most strongly, and it seemed to the National Geographic Society's o party that this retreat was not due to a cessation of advance, but wholly to un dercutting by the Copper River, which Rose over six feet between June and Au Q gust because of summer melting of snows and glaciers. We accordingly predicted in August That the ice front in the river would re p advance the latter part of September, w when the river was lower. This predic tion proved correct, the ice front advanc Sing 390 feet up to October 5, plus the Amount of additional retreat between August 17 and the date when the ad vance commenced, the level of the river B having fallen nine feet meantime. As x the middle of the glacier advanced 390 3 feet in the 49 (lays between August 17 Sand October 5, the minimum rate of actual advance was fully eight feet a day, E if there was advance on each of these w days. As (a) icebergs were discharging Small the time and melting was in progress; as (b) the advance was surely over 300 feet; and as (c) the forward movement began not on August 17, but probably after the middle of September. when the river was much lower, the rate of ad vance was much faster and may easily have been 30 feet a day, as previously estimated.