Dr. Rick Behl - March Speaker

Abstract

Large volcanic eruptions like Tambora (1816) or Krakatoa (1883) influenced the composition of the upper atmosphere and modified the radiation balance of the entire Earth. These produced the “year without summer” and fabulous crimson-hued sunsets immortalized in paintings from the 19th century. It is postulated that much larger supervolcano eruptions like Toba (74 ka) would produce even greater global “volcanic winter” effects. Researchers have created computer models of the possible effects but there is scant data on the actual result of such catastrophic eruptions.
The sedimentary paleoclimate record from Santa Barbara Basin provides an unprecedented high-resolution climatic history of the last Yellowstone supervolcano eruption, one of the largest of the Quaternary. The Lava Creek B ash (631.3 +/- 4 ka), identified by its unique geochemical fingerprint, occurs as two tephra layers, distinct in sediment composition and particle size from the background organic-rich hemipelagic mud. This ashfall deposit records the massive explosive volcanic episode that formed the present Yellowstone volcanic caldera. Our decadal-resolution climate record demonstrates that the volcanism was precisely coincident with, and therefore likely the cause of, two episodes of abrupt sea-surface cooling of ~3 degrees C in Santa Barbara Basin that started and stopped abruptly. Each of these volcanic winters lasted at least 80 years, far longer than predicted by computer models based on atmospheric dust and sulfur loads. These results suggest involvement of strong, positive climatic feedbacks including surface albedo, ice and oceanographic effects.