J. D. Dana — History of Changes in Mt. Loa Craters. 167 



Art. XVII. — History of Changes in the Mt. Loa Craters / by 

 James D. Dana. 



[Continued from page 112.] 

 RELATIONS OF KILAUEA TO MT. LOA. 



The position of Kilauea " on the flanks of Mt. Loa," 9500 

 feet below the level of the summit, plainly suggests the idea of 

 its later and dependent origin. If the two were begun at the 

 same time, why, it is naturally asked, should not Kilauea have 

 approximately the same size as Mt. Loa ? With the same time 

 to grow in, and a distance between the two nearly equal to that 

 between Kea and Loa, and a crater as large and still active, 

 would it have stopped at less than one-third the height and 

 have raised its summit only 300 feet, at the best, above the 

 Mt. Loa slopes ? 



Several of the islands, Oahu, Molokai, Maui, and perhaps 

 also Kauai, consist of two volcanoes united at base, or are vol- 

 canically twins ; and Hawaii is a double twin, one couplet' con- 

 sisting of Kohala and Kea, and the other of Hualalai and Loa, 

 provided Kilauea is subordinate to Mt. Loa. In all the twins 

 the eastern of the two combined volcanic mountains is the 

 larger. But Kilauea, although the eastern on Hawaii and the 

 easternmost of the whole group, is one of the smallest. The 

 greater size of the eastern volcano in a couplet has come from 

 its continuing longer in action ; and this is proved not simply 

 by the size, but also by the evidence of long extinction, and 

 therefore long exposure to denuding agents, in the western 

 mountain ; that is by the depth and extent of the valleys of 

 erosion, the time-marks, over it.* There is other evidence also 



* As this evidence of the lapse of time is important, T here cite a few sentences 

 from the chapter in my Exploring Expedition Geological Report, on the " Origin 

 of the Valleys and Ridges of the Pacific Islands," pp. 37-9-392. 



" Mount Loa, whose sides are still flooded with lavas at intervals, has but one 

 or two streamlets over all its slopes, and the surface lias none of the deep valleys 

 common about other summits. Volcanic action has had a smoothing effect, and 

 by its continuation to this time, the waters have had scarcely a chance to make a 

 beginning in denudation. Mount Kea, which has been extinct for a long period, 

 has a succession of valleys on its windward or rainy side which are several hun- 

 dred feet deep at the coast and gradually diminish upward, extending in general 

 about half or two-thirds of the way to the summit. But to westward it has dry 

 declivities, which are comparatively even at base, with little running water. A 

 direct connection is thus evinced between a windward exposure and the existence 

 of valleys. And we observe also that the time since volcanic action ceased is 

 approximately or relatively indicated ; for it has been long enough for the valleys 

 to have advanced only part way to the summit. Degradation from running water 

 would of course commence on such slopes [windward slopes] at the foot of the 

 mountain, where the waters are necessarily more abundant and more powerful in 

 denuding action, in consequence of their gradual accumulation on their descent. 



" Haleakala, or eastern Maui, offers the same facts as Mount Kea, indicating 

 the same relation between the features of the surface and the climate of the dif- 



