Why Campi Flegrei?
The Campanian Ignimbrite is a rock unit that was emplaced from a dilute pyroclastic density current that accompanied caldera collapse of the Campi Flegrei volcano. The currents reached over 80 km from the vent area and the fallout covers 3.5 million km2, reaching at least 2500 km from the vent. Abundant gas is needed to produce a current that was apparently more than a kilometer thick, but where did this gas come from? Recent work by some of our team found that emplacement temperatures of the Campanian Ignimbrite were above 580 °C, indicating that the current did not cool off very much during transport, which in turn implies minimal entrainment of atmospheric gases and a very short eruption duration. Magmatic gases are likely important, but very high levels of dissolved gas prior to eruption would be needed if that is the only source. Supercritical hydrothermal water (estimated at 500 °C at 5 km depth today) may be an additional gas source.
Simplified geologic map of the Campi Flegrei area with calderas outlined. Modified from Vitale and Isaia (2014). Precise caldera boundaries are still being defined and the size of collapse is debated.
Our scientific aims are: 1) detailed field investigations to better characterize the Campanian Ignimbrite stratigraphy, in order to link distal and proximal deposits and to define the relative timing of volcanic events; 2) a detailed petrologic study of CI products, notably by performing complete volatile analysis (H2O, CO2, S, F and Cl) of melt inclusions and apatite microphenocrysts via Fourier Transform Infrared (FTIR) spectroscopy, ion probe, and electron microprobe; and 3) an experimental investigation of the cooling rates of CI eruptive products, using a technique that studies the glass transition temperature at varying strain rates and residual water contents.
Caldera wall at Campi Flegrei showing the thickness of the Campanian Ignimbrite.
The Naples area has one of the highest volcanic risks in the world, with about 4 million people living in the area that was affected by the Campanian Ignimbrite (ignoring the people living in the fallout zone – >100 million). Understanding the magmatic/hydrothermal conditions that led to such a high-mobility current would allow a better assessment of the risks as current conditions change. Our team is working with personnel from the Osservatorio Vesuviano, so our results will be incorporated into their risk assessments. This joint NSF/NERC project is fostering a significant international collaboration between the US, UK, and Italy and incorporates the education of underrepresented groups in the form of PhD/MS students and post-doctoral researchers.
Our Fieldwork
Our team went into the field to collect samples from within and around the Campi Flegrei caldera in March, 2019 and again in May, 2019. Working with our team members and colleagues from Naples and Rome, we have collected dozens of samples representing various phases of the Campanian Ignimbrite eruption.
Rose Gallo collects ash samples. Gallo is in the process of analyzing the samples for chemistry and morphology in order to correlate proximal and distal deposits from the CI eruption.
Sample Analysis
Several lines of analysis are being undertaken on samples collected in the Campi Flegrei region.
Correlating proximal and distal deposits
Masters Student Rose Gallo is leading a study using the chemistry and morphology of ash and lithics from Campanian Ignimbrite deposits to correlate proximal and distal rock units. Similar deposits can be seen near to and far from the volcanic vent, but field relationships are unclear as to whether these units stratigraphically correlate.
Relevant publications: Gallo R, Iacovino K, Ort MH, Silleni A, and Barbero A (2019) “Correlating the Campanian Ignimbrite using matrix glass geochemistry and morphology” AGU Fall Meeting.
Image of polished pumice collected by R. Gallo under a reflected light microscope.
Using melt inclusions to quantify the volatile budget of the CI eruption
Kayla Iacovino is leading an investigation of the volatile budget (or amount and composition of gas released) of the Campanian Ignimbrite eruption. To do this, Iacovino and the team will measure the chemistry of melt inclusions, tiny blebs of glass representing bits of liquid magma trapped inside of crystals. Melt inclusions store information about the deep magma plumbing system, where volatile elements such as H2O, CO2, S, F, and Cl drive explosive volcanism. Alongside apatite measurements (see below) and together with thermodynamic modeling, this study seeks to quantify all sources of gases from the CI, which fueled the explosive nature of the eruption and sustained hot pyroclastic flows for several kilometers and over high terrain.
Microscopic image of a glassy melt inclusion (round feature in upper left) inside of a quartz crystal collected by K. Iacovino.
Apatite crystals as recorders of volatiles in CI magmas
Principal Investigator Victoria Smith is leading a study using apatite crystals to assess pre-eruptive volatiles budgets of CI magmas. In tandem with melt inclusion measurements (see above) and thermodynamic modeling, this study will quantify the amount and composition of gas that fueled the CI eruption. Melt inclusions can lose information about the deepest magmatic volatiles as they are easily “reset” during shallow storage. Apatites remain robust record keepers of magmatic volatiles where melt inclusions fail. Together, the two can tell the story of magmatic volatile content during storage in the crust prior to eruption as well as the sequential ascent, degassing, and eruption of CI magmas.
Schematic of the subsurface magmatic plumbing system at Campi Flegrei, based on apatite and glass compositions. From Stock et al., 2018.