Volcanic Emissions

Volcanoes inject both gases and particles into the atmosphere. This material can modify atmospheric composition and so change the chemical and radiative balance of the atmosphere. The radiative changes induced by volcanic eruptions result in perturbations of the Earth’s climate over the local to global scale as well as over a range of periods from hours to millennia. In general the study of active volcanism on Earth can be broken down into

• the monitoring of quiescent volcanism releasing gases, lava and small amounts of ash,
• observations of large volcanic events that eject large quantities of gas and ash into the atmosphere which have effects on the regional to global scale.

The principal gases released by volcanic activity are H₂O, CO₂, CO, SO₂, H₂S, S₂, HCl, HF, H₂. Volcanoes are one of the principal sources of atmospheric SO₂ and so are important to the atmospheric sulphur budget. One of the consequences of large eruptions injecting large amounts of SO₂ and H₂S into the atmosphere is the formation of drops of H₂SO₄ from the oxidised gases. These aerosol particles alter the atmospheric radiation field by scattering solar radiation, and by absorbing infrared radiation. For example the eruption of Mt Pinatubo in the Philippines in 1991 is estimated to have cooled the average surface temperature of the Earth by 1.5 C.

An eruption also ejects molten and solid rock fragments (tephra) into the air. The large fragments fall back to the ground near the vent but the fragments with a diameter less than 2 mm, called ash, can remain suspended in the atmosphere from days to weeks. In the troposphere ash particles additionally act as cloud condensation nuclei and so have an indirect effect on the radiation budget by modifying the radiative properties of cloud.

Several jet airplanes have been damaged by encounters with drifting clouds of volcanic ash. Casadevall (1994) reported 80 cases in 20 years. The natural variability of volcanism implies that there will be high year-to-year variability about the average. At least two commercial passenger aircraft have had all engines fail following flight into an unanticipated volcanic ash cloud during those 20 years (for example BA flight 9). Most aircraft ash encounters occur where the volcanoes are relatively isolated.

Scientific Challenges & Questions Motivating EODG Research

Within the EODG we are interested in

• Measuring the refractive index of volcanic ash and understanding how this varies as a function of volcanic processes.
• Identify ash and retrieving ash plume height, amount, optical depth and particle size from satellite measurements.
• Identifying SO₂ (and other volcanic gases) and quantitatively retrieving SO₂ plume height and amount from satellite measurements.
• To exploit satellite measuremnts of volcanic emissions to
  • relate changes in amount and type of material to the underlying volcanic processes,
  • quantify the volcanic contribution to the atmospheric sulphur budget,
  • understand how volcanic material evolves and dissipates once in the atmosphere,
  • build a long term record of volcanic emissions and to try and identify patterns of behaviour,
  • provide a near real time atmospheric anomaly alert system of volcanic emisisons.

and for fun ...

Three Ways to Melt the Mantle

Maintained by Don Grainger