USGS Preliminary Analysis_LERZ_7-15-18_v1.1

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A few weeks later, after a substantial edifice, filled with ponded lava, had grown around the dominant vents, two new fissures opened to the east of, and along the same trend as, the initial line of fissures. This may have been due to an increase in head pressure in the magmatic system in response to construction of the tephra cone complex and ponded lava. The lava chemistry changed from more -evolved (stored magma) to fresher (directly from the summit reservoir) about half way through the eruption. This did not seem to cause a change in eruptive behavior. The dying phase of the eruption lasted from Feb 7 to 20, with a marked reduction in discharge. While slow deflation at the summit began about 4 days after the eruption started, summit collapse really began in earnest on about February 7, coincident with the start of the dying phase of the eruption. About 122 x 10 to the 6th power meters cubed of lava was erupted. The time-averaged discharge rate was about 38 meters cubed per second during the first two weeks of the eruption. 15