The Magnitude of the 39.8 ka Campanian Ignimbrite Eruption, Italy: Method, Uncertainties and Errors

Aurora Silleni,Guido Giordano,Roberto Isaia,Michael H Ort

doi:10.3389/feart.2020.543399

Abstract

The 39.8 ka Campanian Ignimbrite eruption is the largest caldera-forming eruption of the Campi Flegrei and had a global-scale impact on the environment and human populations. The cooling following the eruption and its widespread tephra strongly affected the paleoenvironment and the migration of hominids in Europe. Despite a large number of studies, the Campanian Ignimbrite Dense Rock Equivalent (DRE) volume estimates range from 60 to 300 km3. Here we present a review of the previous volume evaluations and a new calculation of the volume of the ignimbrite. This estimate is constrained by the first total isopach map of the Campanian Ignimbrite PDC deposit preserved on land, developed through a method that reconstructs the paleo-topography at the time of the eruption. The method is reproducible for all strongly topographically controlled ignimbrites and allows the calculation of well-defined uncertainties in the on-land ignimbrite deposits. The preserved total extra-caldera bulk volume of the ignimbrite is estimated at 68.2 km3 ± 6.6 km3. The total PDC deposit volume is then corrected for erosion, ash elutriation, the intracaldera deposit volume and the volume of tephra deposited in the sea, and volumes of fallout are taken from other studies. The final total volume estimate of the eruption ranges from 177 km3 – 265 km3 DRE. This value corresponds to a mass of 4.6 - 6.9 x 1014 kg, a magnitude (M) of 7.7 – 7.8 and a volcanic explosivity index (VEI) of 7. The new detailed estimate of the Campanian Ignimbrite eruption physical parameters, for the first time constrained by the ignimbrite deposit, confirms the magnitude of this event.

Highlights

Pyroclastic density currents (PDCs) have large impacts on human communities and the environment; they can cause catastrophic environmental and property damage and loss of life, as well as accounting for a large proportion of deaths caused by direct volcanic activity
We demonstrate a rigorous method to create a complete isopach map of the Campanian Ignimbrite (CI), with a similar approach to that normally applied to tephra-fall deposits (e.g., Engwell et al, 2015) and it can be used on other ignimbrites in the world
The 0 m isopach was traced to enclose all the mapped CI and areas that probably have the CI below the recent sedimentary cover, they have a slope less than 15° and they are in contact with mapped CI outcrop

Summary

Introduction

Pyroclastic density currents (PDCs) have large impacts on human communities and the environment; they can cause catastrophic environmental and property damage and loss of life, as well as accounting for a large proportion of deaths caused by direct volcanic activity. Global and regional climatic effects can result from the injection of ash and sulfur aerosols into the stratosphere during large explosive eruptions, leading to a “volcanic winter” (Rampino and Self, 1992; Stuiver et al, 1995; Thordarson and Self, 1996; Robock, 2000). The quantitative computation of the size of explosive eruptions is essential to understand their potential impact on humans, climate and ecosystems (e.g., Mason et al, 2004). Calculating the volume of large volcanic eruptions is necessary to define their size (e.g., Newhall and Self, 1982; Pyle, 2000; Crosweller et al, 2012; Pyle, 2015) and to model the climate effects of these natural phenomena that occurred in the past. The resulting tephra volumes appear to be better constrained than ignimbrite volumes, where a clear “reference” method does not exist and uncertainties on such computations are significant (Mason et al, 2004)

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