Throttling back the great lava floods?

Kerr, Richard

'But Self and his students think they have found clues that mark the Columbia River flood basalts as slow-moving pahoehoe after all. Among them are 'spiracles'—partially filled vertical tubes. Other researchers had explained spiracles as the result of steam blasting up through the lava as it flowed over swampy ground. But recent observations on Kilauea suggest that similar structures might form in pahoehoe. The process that might be responsible was recently documented by Ken Hon of the U.S. Geological Survey (USGS) in Denver and his colleagues. An advancing sheet of lava a few tens of centimeters thick stalls as its crust thickens, but magma continues to push under the crust, lifting it and inflating the flow to a thickness of from 1 to 5 meters. George Walker of the University of Hawaii went on to suggest that when two abutting lobes of pahoehoe lava inflate, fingers of lava are injected into the growing suture between the lobes, forming spiracle-like columns. Self and his colleagues think the same suturing process operated in the Columbia River flows—along with the tube formation that allows pahoehoe to flow long distances. The tubes, they say, are hard to see because on the gentle slope of the plateau the broad thin tubes probably never drained, so that little was left to mark their presence.'--p. 662

Throttling back the great lava floods?

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