Andrew Todd Calvert, Ph.D.

Research Accomplishments

Eruptive history of Cascade and Aleutian Arc Volcanoes, an example from the Three Sisters

Most mapped volcanoes appear to be built episodically and characterizing these episodes offers insight into future eruptive behavior. Middle Sister is the most chemically diverse and youngest of the Three Sisters Volcanic Cluster (Hildreth et al., 2012).  Dated, mapped lava flows precede and postdate the remarkably productive (fourfold increase in output between 50 – 15 thousand years) and silicic rhyolite episode best exposed at South Sister.  Our Middle Sister paper (Calvert et al., 2018) chronicles mafic, intermediate and silicic eruptions from peripheral and central vents and compares timing and compositions with the largely-silicic products of South Sister (Fierstein et al., 2011).   

Growth of Hawaiian volcanoes

Despite being some of the best-studied volcanoes on earth, little was known about the inception ages and lifespans of Hawaiian volcanoes, largely because early-erupted samples are inaccessible and all samples are difficult to date accurately and precisely. The chemical progression from alkalic to tholeiitic and back to alkalic compositions is well-characterized, yet the timescales of this variation have been difficult to constrain. Even volume estimates vary significantly because a new edifice may develop on the flank of an older shield.  A collaborative agreement between USGS and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) provided submersible access to early-erupted materials and a unique opportunity to constrain inception ages and compositional evolution rates of the most productive volcanic center on earth. 

We undertook to date submarine samples from the south flank of Kilauea, Mahukona and Hilo Ridge to develop a basic framework for the time-volume development of Hawaiian volcanoes. Lavas from an intact section of weakly alkalic basalts on submarine flank of Kilauea and strongly alkalic blocks from debris flows beneath Kilauea are indistinguishable at 147±14 ka and older strongly alkalic samples range from 212±38 ka to 280±20 ka (Calvert and Lanphere, 2006).  This finding shows that Kilauea is a relatively young volcano and the voluminous younger, tholeiitic lavas were erupted at higher rates than generally assumed.  This work refutes previous studies dating the tholeiitic lavas at 500 ka along the active rift zone and in drill core. Weakly-alkalic rocks from Hilo Ridge yielded 1150±20 ka ages, far too old to belong to their assumed source, Mauna Kea.  Hilo Ridge instead belongs to Kohala volcano, which is now estimated to have erupted from 1,200 to 280 ka (Lipman and Calvert, 2011).  Mauna Kea had been reported to be more voluminous than other centers on Hawaii, however, this result requires that the submarine Hilo Ridge belongs to Kohala, not Mauna Kea, reducing the estimated eruptive volume of Mauna Kea by nearly 50% (42 to 22 km3) a