Revision History for U.S. Geological Survey Fact Sheet 2019-3023 By Lee Siebert, Mark E. Reid, James W. Vallance, and Thomas C. Pierson When Volcanoes Fall Down—Catastrophic Collapse and Debris Avalanches ----------------------------------------------------- Posted online May 8, 2019 ----------------------------------------------------- Revised and reposted June 2019 Page 5 - The missing word "ridge" was added to the sentence, "The rapidly moving avalanche had sufficient momentum to overtop the 380-m (1,250 ft)-high Johnston Ridge (named for U.S. Geological Survey volcanologist David Johnston, who observed the initial moments of the eruption from his observation station near the crest of the ridge before he was overtaken by the lateral blast)." Page 6 - The view in the photograph of Mount Shasta was shifted slightly to make the water feature more visible. ----------------------------------------------------- Revised and reposted August 2019 Page 5 - Mount St. Helens map figure. A geographic feature on the map was incorrectly labelled "Wavy Ridge." The correct label (Windy Ridge) has been applied.