By 1918 and 1919 the pit was full and overflowing the Kilauea floor. During the whole of 1919 Halemaumau, as a pit, was obliterated by its dome of fill. In autumn the south flank of Mauna Loa broke out again, into a flood of lava that reached the sea in South Kona. Remembering 1916, we predicted that, even though Halemaumau was full to the brim, the sinking away of Mauna Loa lava would pull down Kilauea lava suddenly, like a siphon. Exactly this happened on November 28, 1919. During the night the crags, the clover-leaf lake, and the bulging dome of the lava fill above Halemaumau’s edge went down as a cylinder to a depth of 400 feet in two or three hours leaving incandescent avalanching walls, a gratifying confirmation of theory. As in 1916, the Halemaumau lava immediately returned to the bottom of the pit, and lifted itself thirty feet a day for three weeks, so that in December it was a violently boiling ringshaped puddle, surrounding a horseshoe of crags with a quiet inner lagoon and resembling a coral atoll. The Kilauea floor, which is dome-shaped outside of Halemaumau, split open radially to the south, made floods of lava into the Kilauea Crater wall valley, and even escaped out into the Kau Desert. This was extended into a mountain crack, making flank lava flows of Kilauea Mountain, nine miles away to the southwest, something which had not happened since 1823 and 1868. Concentric craters like Kilauea caldera and Halemaumau pit are thus ring-in-ring, or cup-in-cup, structures by means of slag heapings over a deep fracture in the rock crust, the circularity determined by occasional central sinking. This circularity has sometimes reached perfection. In 1894 and 1909 the liquid pool inside Halemaumau, by steady welling up about a central hole, became perfectly circular within a circumferential rampart of overflow. This is a rare condition dependent on steadiness of upwelling, temperature, and viscosity. It is important because it shows how the perfect circles, and rampart cauldrons, were made on the moon, where there are also angular calderas of subsidence like Kilauea Crater. Evidently gas heating and liquidity changed on the moon, just as it has done in Hawaii. The sources there are over cracks, as in Hawaii. The analogies are so complete in these and many other ways that I completely disbelieve in meteor impact for the moon craters. The moon awaits a complete comparison with active terrestrial basaltic lavas, by a modern volcanologist.