Microscopic view of different groundmass textures in rocks. On the left, this groundmass is a good choice for argon dating, as it consists of abundant interconnected crystals. On the right, the groundmass consists predominantly of glass (black because it does not transmit cross-polarized light) and is a poor choice for argon dating.
Andrew Todd Calvert, Ph.D.
As Scientist-in-Charge of the California Volcano Observatory (CalVO), I lead the ~35 geologists, geophysicists and hydrologists that study and monitor volcanoes in California and other domestic and international volcanoes. CalVO also maintains laboratories to study many aspects of volcanic behavior. CalVO is located in Menlo Park and Moffett Field on the San Francisco Peninsula.
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
Education and Certifications
Ph.D., University of California – Santa Barbara
Dissertation: Metamorphism and exhumation
M.S./B.S., Stanford University (both degrees conferred June 1992)
Thesis: Structural Evolution and Thermochronology of the Kigluaik Mountains, Seward Peninsula, Alaska
Science and Products
Datasets documenting late Pleistocene faulting in the Pondosa fault zone, Pit River Region, Northeastern California
Argon geochronology results for Reconnaissance basement geology and tectonics of North Zealandia
Dataset Establishing Temporal Duration of Two Shield Volcanoes in Northern California
Database for the Geologic Map of Three Sisters Volcanic Cluster, Cascade Range, Oregon
Chemical and isotopic analyses of Mount Shasta, California
Geologic map of Three Sisters volcanic cluster, Cascade Range, Oregon
The cluster of glaciated stratovolcanoes called the Three Sisters—South Sister, Middle Sister, and North Sister—forms a spectacular 20-km-long reach along the crest of the Cascade Range in Oregon. The three eponymous stratocones, though contiguous and conventionally lumped sororally, could hardly display less family resemblance. North Sister (10,085 ft), a monotonously mafic edifice at least as ol
Microscopic view of different groundmass textures in rocks. On the left, this groundmass is a good choice for argon dating, as it consists of abundant interconnected crystals. On the right, the groundmass consists predominantly of glass (black because it does not transmit cross-polarized light) and is a poor choice for argon dating.
The east face of Middle Sister is 350 m (1150 ft) high. Ice-sculpted pile of lavas at right, variously called "Black Hump," "Prouty Point," or "Step Sister," has 190 m of relief and consists of at least five flows.
The east face of Middle Sister is 350 m (1150 ft) high. Ice-sculpted pile of lavas at right, variously called "Black Hump," "Prouty Point," or "Step Sister," has 190 m of relief and consists of at least five flows.
Aerial photo of Mount Shasta's southwestern flank in a low-snow period. The Hotlum cone is on the right, while the Shastina dome is to the left.
Aerial photo of Mount Shasta's southwestern flank in a low-snow period. The Hotlum cone is on the right, while the Shastina dome is to the left.
Active volcanism on the Arabian Shield—Geology, volcanology, and geophysics of northern Harrat Rahat and vicinity, Kingdom of Saudi Arabia
The Saudi Geological Survey-U.S. Geological Survey northern Harrat Rahat project—Styles, rates, causes, and hazards of volcanism near Al Madīnah al Munawwarah, Kingdom of Saudi Arabia
Cenozoic tectonics of the western Arabia Plate related to harrat magmatism near Al Madīnah, Kingdom of Saudi Arabia
Eruptive history of northern Harrat Rahat—Volume, timing, and composition of volcanism over the past 1.2 million years
The duration and characteristics of magmatic differentiation from basalt to trachyte within the Matan volcanic center, northern Harrat Rahat, Kingdom of Saudi Arabia
Explosive trachyte eruptions from the Al Efairia volcanic center in northern Harrat Rahat, Kingdom of Saudi Arabia
Mantle origin and crustal differentiation of basalts and hawaiites of northern Harrat Rahat, Kingdom of Saudi Arabia
Paleomagnetically defined brief lifespans for two large shield volcanoes in the Cascades Arc
Precaldera mafic magmatism at Long Valley, California: Magma-tectonic siting and incubation of the Great Rhyolite System
Trachyandesite of Kennedy Table, its vent complex, and post−9.3 Ma uplift of the central Sierra Nevada
Simultaneous Middle Pleistocene eruption of three widespread tholeiitic basalts in northern California (USA): Insights into crustal magma transport in an actively extending back arc
The remarkable volcanism of Shastina, a stratocone segment of Mount Shasta, California
Science and Products
Datasets documenting late Pleistocene faulting in the Pondosa fault zone, Pit River Region, Northeastern California
Argon geochronology results for Reconnaissance basement geology and tectonics of North Zealandia
Dataset Establishing Temporal Duration of Two Shield Volcanoes in Northern California
Database for the Geologic Map of Three Sisters Volcanic Cluster, Cascade Range, Oregon
Chemical and isotopic analyses of Mount Shasta, California
Geologic map of Three Sisters volcanic cluster, Cascade Range, Oregon
The cluster of glaciated stratovolcanoes called the Three Sisters—South Sister, Middle Sister, and North Sister—forms a spectacular 20-km-long reach along the crest of the Cascade Range in Oregon. The three eponymous stratocones, though contiguous and conventionally lumped sororally, could hardly display less family resemblance. North Sister (10,085 ft), a monotonously mafic edifice at least as ol
Microscopic view of different groundmass textures in rocks. On the left, this groundmass is a good choice for argon dating, as it consists of abundant interconnected crystals. On the right, the groundmass consists predominantly of glass (black because it does not transmit cross-polarized light) and is a poor choice for argon dating.
Microscopic view of different groundmass textures in rocks. On the left, this groundmass is a good choice for argon dating, as it consists of abundant interconnected crystals. On the right, the groundmass consists predominantly of glass (black because it does not transmit cross-polarized light) and is a poor choice for argon dating.
The east face of Middle Sister is 350 m (1150 ft) high. Ice-sculpted pile of lavas at right, variously called "Black Hump," "Prouty Point," or "Step Sister," has 190 m of relief and consists of at least five flows.
The east face of Middle Sister is 350 m (1150 ft) high. Ice-sculpted pile of lavas at right, variously called "Black Hump," "Prouty Point," or "Step Sister," has 190 m of relief and consists of at least five flows.
Aerial photo of Mount Shasta's southwestern flank in a low-snow period. The Hotlum cone is on the right, while the Shastina dome is to the left.
Aerial photo of Mount Shasta's southwestern flank in a low-snow period. The Hotlum cone is on the right, while the Shastina dome is to the left.