Patterns of volcanism in the Cascade Arc during the past 15 000 years

About 110 well-dated and 70 poorly dated eruptive periods less than 15 000 years old at individual volcanoes in the Cascade Arc constitute a data set for identifying spatial and temporal patterns of eruptive activity. Key features of the record include: 1) the mean frequency of eruptive periods during the past 4000 years is approximately two per century; however, the variance about the mean may be large; 2) at most major centres, episodes of activity lasting several thousand years are defined by groups of eruptive periods separated by apparent dormant intervals of roughly similar duration, 3) arc-wide clustering of eruptive activity may exist at 0-4 ka, 6-8 ka, and 10-14 ka. Such clustering would be remarkable in light of significant along-arc changes in crustal structure, stress field, and subduction-zone geometry. -Author