SYMPATHY BETWEEN MAUNA LOA AND KILAUEA.
Much has been written upon the question as to how our two great volcanoes stand related to each other. Attempts have been made to show a species of parallelism in the volcanoes of the archipelago—the latest are by Professor Dana representing that Kaala, West Molokai, Lanai, Kahoolawe, Hualalai and Mauna Loa lie along one line, while the greater series is from Kauai through Koolau, East Molokai, Maui, Kohala and Mouna Kea to Kilauea. Mr. Green proposes the tetrahedral scheme, accord ing to which all the volcanoes are near the intersections of two out of three sets of fissures disposed at angles of sixty degrees to each other. Both schemes agree in granting separate existence to Mouna Loa and Kilauea ; the latter is not an appendage to the former.
The similarity of the rocks indicates a consanguinity. Both carry basalts with or without olivine, the same specific gravity and various minute details of composition.
Both are calderas and discharge their lava in similar ways.
But the main question is still, why should there exist only twenty miles apart two columns of liquid lava approximately Io,000 and 3,50o feet in altitude above the sea ? If both come from the same reservoir why should not the discharge be from the end of the lower arm of the syphon, especially when the upper arm is filled? Or why should there not be a sympathetic action between the eruptions ? Observers have often said that one vol cano was asleep while the other was in action.
Mr. Green endeavors to show by experiments that liquids of different densities will not necessarily stand at the same level when connected in separate upright glass tubes joined to a hori zontal pipe containing a basal fluid. His assumption is that there is a variation in the densities of the Hawaiian lavas sufficient to sustain columns of varying lengths, particularly when they have different diameters ; the smaller tubes suffer a greater proportion ate loss of heat. The tempeature is maintained by convection currents. But he insists that a rise in the Mokuaweoweo column would not necessarily cause the Kilauea lavas to ascend ; so that the sympathy supposed to exist would not be displayed.
The best starting paint in this discussion is a comparison of the correspondencies and differences between the eruptions of these neighboring volcanoes, citing only those that are well known.
Averaging the figures so that when the eruptions occur exactly synchronously or during the same calendar years they will be on the same horizontal line, and having the eruptions that do not agree placed between the others, the conclusions suggested are almost startling.
First the years of agreement are 1832, 1849, 1855, 1868, 1877, 1887, 1907. Three of those upon Mauna Loa, 1868, 1887, 1907, broke out only low down and were preceded by severe earth quakes. The most natural suggestion is that the simultaneous discharges were occasioned by the great depths of the lava: the mountain having refused to yield to pressure higher up. Be cause the pressure was intense the earthquakes were violent and fissures were produced, and the discharges though voluminous were effected very briefly. The 1855 eruption from Mauna Loa was one of the largest ever known. Those of 1832 may have been synchronous and not six months apart, as has been stated previously. The light on Mokuaweoweo in May, 1849, was not observed till after the fire was conspicuous at Kilauea, and Mr. Coan was not able to say that they were coincident, though the statement implies it. There have been, therefore, seven erup tions that were synchronous upon the two mountains. Second, upon the supposition that both columns had the same basal sup port, the discharge in the times between the joint eruptions was confined to one of the two volcanoes, the pressure not being suffi cient to render both active. And there has usually been an alter nation from one to the other. The greater column has sustained nine of the intermediate discharges, in 1843, 1851-2, 1859, 1865-6, 1872-7, 188o-1, 1896, 1899 and 1903; Kilauea has been active seven times, in 1866, 1879, 1886, 1891, 1894, 19o2 and 1908. There may have been fire in Mokuaweoweo in 1823 and 1840 un recorded, because of the absence of observers or because of con cealment by clouds. Just why one or the other of these columns should have been affected to the exclusion of the other is not ap parent.