Supereruptions Happened In Surprisingly Brief And Powerful Bursts

Massive volcanic eruptions have shaped Earth’s climate and coincide with many major mass extinctions in the past 300 million years. These supereruptions flooded vast areas with lava in a mere 2 to 5 million years, leaving behind extensive areas covered by igneous rock that geologists call flood basalt provinces or Large Igneous Provinces (LIPs). To better understand the dynamics of LIPs, and thus accurately assess their impacts, the duration of individual LIP eruptions need to be measured at the scale of years to decades. This is difficult to accurately document in the field, as single eruptions tend to merge together, forming an apparent uniform igneous rock formation.

In a new study, researchers of Idaho State University, University of Oregon, University of Wyoming and New York’s Columbia University developed a new approach using diverse thermochronologic, paleomagnetic, and stable isotopic data to measure how long a dike in the Columbia River Flood Basalt Province actively transported magma.

The analyzed dike is located in the Wallowa Mountains, Oregon, part of an extensive and complex labyrinth of dikes spanning the entire mountain range, which fed the main eruptive phase of the Columbia River Basalt Province about 16 million years ago.

The Columbia River basalts form the youngest, smallest and one of the best-preserved continental flood basalt province on Earth, covering over 210,000 km² of mainly eastern Oregon and Washington, western Idaho, and part of northern Nevada.

Thermochronology measures the time since a mineral cooled below a “closing temperature”, no longer able to absorb or release chemical elements. It provides researchers with the age when the magma solidified. The iron-rich minerals magnetite and hematite have the unusual property of recording the direction of the magnetic field that they formed in. This remanent magnetization can be reset by heating up the rock hosting the minerals. Dike segments that actively transported magma for long periods transmit more heat into the surrounding country rock and should reset all remanent magnetization. Short-lived dike segments either would not transmit enough heat to reset any country rock, or the effect is limited to a thin rim around the dike (rocks are notoriously bad conductors for heat). Paleomagnetic measurements allow to estimate how long magma was actively flowing in a dike. Stable isotopic signatures of oxygen and hydrogen observed in the country rocks next to dike segments can provide independent evidence for hydrothermal fluid flow, altering the chemical composition of the rocks or delaying the cooling of the dikes and country rocks.

The surprising finding? The feeder dike was actively flowing for less than 10 years, maybe even less than 2 years.

Based on the dimensions of the studied feeding dyke and duration of active magma flow, the authors calculated a flow rate of 1 to 6.1 km³/day. This rate is likely at least an order of magnitude larger than that of the 1783 Laki fissure eruption (the largest land-based effusive eruption in historic times) and two orders of magnitude larger than the 2018 Kīlauea eruption. But in the historic eruptions, volcanic deposits formed from a combination of many active fissures and eruption phases lasting for many years, meanwhile the flood basalts were formed by short-lived bursts erupting large volumes of lava at once.

Based on the area covered by lava, there were more than 350 lava flows active over time, feed from fissures ranging from tens to hundreds of kilometers in length, located along the Washington/Oregon/Idaho border.

The magma that fed these massive eruptions may have come from a plume-like upwelling from the mantle called a hot spot. Since the time of the eruptions, the North American plate has moved in a west-southwestwardly motion, and that hot spot is now believed to reside beneath Yellowstone volcano in northwest Wyoming.

The full study, “Co-inversion of multiple thermochronometers and a paleomagnetic thermometer at a Columbia River flood basalt feeder dike (Oregon, USA) demonstrates the sensitivity of thermal history results to diverse data constraints,” was published in the journal Geosphere and can be found online here.