At Vulcan's shoulder; James Dwight Dana and the beginnings of planetary volcanology

Abstract

J. D. Dana was a pioneering American naturalist who put an impressive stamp on four fields-mineralogy, zoology, volcanology, and geology-during a long career. Educated at Yale, the seminal event of his post-graduate education was participation in the United States Exploring Expedition in the Pacific between 1838 and 1842. Observations of atolls, volcanic islands, and active Hawaiian volcanoes, together with insights gained from the charting activities of the expedition, enabled him to make the first synthesis of volcanic action in the Pacific and to formulate the broader doctrines of the contrasts between, and the permanence of, continents and ocean basins, and of the historicity of the Earth. The magnitude of Dana9s contribution must be viewed from the perspective of geological sciences in the early 19th century. At the onset of the Exploring Expedition, direct accounts of volcanic action were scant, the Wernerian neptunist view of the aqueous origin of basalt had only just been laid to rest, most geologists still had no clear conception of how basalts erupted from volcanoes, fossil sequences were only beginning to be understood, and both geological mapping and systematic stratigraphy were in their infancy. Dana had little formal training in geology, but his observational skills were already evident in an early description of flowing lava and fire fountaining at Vesuvius (1835). Wide reading had made him familiar with current concepts of continental geologists. Dana was perhaps the first trained naturalist to observe the fluidal character of erupting basaltic lava, this at Kilauea on Hawaii, and he at once understood how this contrasted with the more viscid attributes of lava at Vesuvius. But he was also able to perceive how basaltic eruptions could build a large volcanic island, and to understand that fluvial action and subsidence eventually could reduce a Hawaii to an eroded volcanic stub, sustained as a land area only by the countergrowth of fringing and barrier reefs. Dana identified the linear arrangements of volcanic chains on the sea floor and established their age progressions using extent of erosion and development of offshore reefs. He predicted the existence of the vast tracts of drowned and deeply submerged atolls, now termed guyots, in the western Pacific, and said where they could be found. Dana the geologist was unreservedly historical, a perspective that reflected his Christian opinion of the human estate as the culmination of Divine creation. The geological past was directed toward this moment no less than recorded human history, with a genuine beginning and substantive changes through time. This view contrasted with the uniformitarian (deistic) opinions of Hutton and especially Lyell, who saw processes repeated through an indeterminant length of time but no pattern of fundamental change. Dana9s North American puritan tradition gave him the optimism that an Earth history could be established by human ingenuity and effort, and it persuaded him to devote all his energies to this end. Dana entered the Pacific seeking broad patterns. The first of these he discerned was the interaction of volcanic action, fluvial erosion, subsidence, and coral growth on the islands he explored, leading to formation of atolls. This provided proof of direction in Earth history and a unifying planetary perspective, focused on volcanology, which was first outlined in Dana9s report on Geology for the Exploring Expedition in 1849. Later, through voluminous writing and years of teaching, Dana carried these views to a position of extraordinary influence and importance for all subsequent geological science.