According to new research, the colossal caldera of the Yellowstone supervolcano was created by not one, but two powerful and closely spaced eruptions that took place some 630,000 years ago. The super eruptions were powerful enough to affect the global climate as the planet was recovering from an ice age.
Supervolcanoes, such as the one resting beneath the Yellowstone National Park are capable of generating eruptions that dwarf those of their smaller cousins.
Evidence of the ferocity and magnitude of these eruptions is evident in the sheer size of the 45 x 30 mile (72 x 48 km) Yellowstone caldera – the crater that formed in the wake of the supervolcano's most recent bout of activity.
A team of geologists from the University of California Santa Barbara (UCSB) discovered a new record of the violent events that formed the Yellowstone caldera in two layers of ash and the shell sediments located off the Californian coast.
Underwater conditions in the Santa Barbara basin 630,00 years ago – around the time the explosive volcanic activity took place – was extremely well suited to creating an enduring record of the climate altering events.
This is partially due to the fact that, at the time, the aquatic environment was being fed by nutrients from deep within the ocean, which allowed for a high population of single-celled organisms known as foraminifera. The shells of the foraminifera, discovered in the sediment alongside the volcanic ash, play host to temperature dependent oxygen isotopes that can be used by geologists to determine the temperature of the sea in which they lived.
The low-oxygen environment at the seafloor in the Santa Barbara Basin discouraged the presence of burrowing bottom-dwelling animals that would otherwise have damaged the quality of the record by mixing the ash and sediment layers.
This combination of volcanic ash and shell sediment provided the team with an unprecedented high-resolution record of Yellowstone activity, revealing not one, but two eruptions, with a gap of 170 years in between.
An analysis of the foraminifera shells revealed that, after each of the super eruptions, the Santa Barbara Basin cooled by roughly 3 °C, as ash and volcanic sulfur dioxide released during events prevented light from the Sun from reaching and warming the Earth's surface.
According to the UCSB geologists, these closely spaced volcanic winters took place at a time when Earth was warming up following an ice age. The twin cooling periods, which lasted over 80 years a piece, had the effect of stalling the climate shift.