LUNAR AND HAWAIIAN PHYSICAL FEATURES COMPARED.
Geologists have not been slow to recognize volcanoes in the photographs of the lunar surface taken by astronomers. G. Poulett Scrope presents comparative maps of the craters about Naples and upon the moon, and others have discussed the re semblance between them. In 1905 Professor W. H. Pickering of Harvard Observatory visited the Hawaiian Islands to study their volcanic features, and in 1907 he explored the volcanoes of the Azores, with the intent of learning what light their contours throw upon the lunar craters. He had determined that the lunar craters correspond better with the Hawaiian or "engulphment" type than with the Vesuvian, characterized by explosive erup tions, before starting. The explosive volcanoes have the habit of blowing the craters into fragments in time of eruption ; where as the calderas of Hawaii and the Moon discharge their lavas internally without any important fractures of the walls. The lunar volcanoes are from two to twenty times larger than the terrestrial ones, while the force of gravitation in the Moon is only one-sixth as great as it is upon the Earth. This would allow the former body to support craters much larger than the latter.
Of the three classes of terrestrial craters, the tuff and cinder cones, and the lava craters, only the last need to he studied in this connection, although there are with us examples of the others. The third series may be classified as cones, pits, rings and bowls, most of them very diminutive by the side of their lunar relatives. Other formations are the caves, channels, cracks, blow holes or spiracles, pinnacles and ridges.
Mauna Loa is the finest example of a lava cone, and conceiving the ocean removed, as there is no water in the 1Vloon, it is quite worthy of comparison, with its height of 30,000 feet and a base of one hundred miles. Every island in the archipelago is of the same nature, and usually with several cones present. Bullialdus in the Moon with a crater thirty-eight miles in diameter, has the same general contour. Other examples are Kahakau in Molokai, Kuohi, the sixth crater near Kilauea, Halemaumau, Kilauea-iki and several upon Hualalai. These have no elevated borders, are
simply holes in the ground, and are compared to some of the lunar mania.
The lunar rings are represented by Schickard, Phocylides and the Sinus Iridium, Plate 48AB. The first has a diameter of one hundred and thirty-four miles, with a depth of two miles. The Sinus Iridium is a good illustration of a mare, with a flat top. The rings of Kilauea used by Professor Pickering to illustrate this phase, are the encrusted edges of the lakes of 1891 and 1894. Their rarity upon the earth, compared with their abundance in the moon, may be explained because here they are not perma nent. Upon the moon with a diameter of from twenty to sixty miles and a depth of two miles, the destruction of the walls by fall ing down would not be so common.
The lunar craters have three kinds of floors ; either with a cen tral peak, several small craters or without conspicuous detail. The Hawaiian craters carrying central peaks are uncommon, un less Kilauea with its central cone of Halemaumau may be con sidered as one. Professor Pickering uses several illustrations, see Plate 49, as one near Humuula, Hualalai and east of Kilauea. The ridge along the central line of Haleakala, four hundred feet long and one hundred and fifty feet high may be of this character.
The lava bowls are illustrated by Aloi, the third crater east of Kilauea, and upon Hualalai. Their number upon the moon is very great, being ten times more than all the other depressions combined.
Plate 49 is copied from Professor Pickering's book, illustrat ing the various cones, pits, rings and bowls found in Hawaii which help in the elucidation of the lunar craters. As their rela tive sizes are unimportant I have not copied the detail of their scales.
a-b, Tuff cones of Punchbowl and Diamond Head ; c, cinder cone on Mauna Kea, compare Plate 12B ; d, the caldera of Kilauea from north to south ; e, lava cone in Haleakala, compare Plate IIB ; f, lava pit, sixth crater near Kilauea ; g, lava cone and ring, and h, ring from Hualalai ; i, lava ring with central cone near Humuula ; j, lava bowl on Hualalai ; k, 1, m, n, p, lava piles from Hualalai ; o, Alealea or fourth crater near Kilauea.