Spectrally High resolution Infrared measurements for the characterisation of Volcanic Ash (SHIVA): a new way to study volcanic processes

Ash from explosive volcanic eruptions holds information about magma dynamics within volcanic conduits, in the critical zone where fragmentation occurs and eruption style is decided. Although morphological and petrological features of ash and scoria have provided insights into the mechanisms of explosive basaltic eruptions, important questions on the transition between different mechanisms are still unanswered. Three approaches to understanding ash composition are: plume spectrometry, chemical analysis of bulk plume particle samples and particle microscopy. The first of these techniques is experiencing a step change in its ability to provide insight for two reasons. Firstly, high resolution refractive index data from volcanic ash samples is becoming available through a NERC funded project. While this data is not critical to the project, it allows the refractive indices of samples from a known eruption (e.g. Grimsvötn) to be used to generate the optical properties that are used in the retrieval of the properties of the volcanic ash cloud from satellite measurements. Secondly, high resolution infrared spectrometers now observe the Earth with sufficient frequency that recent eruption in remote locations have been well observed, e.g. the 2011 eruption of Nabro in Eritrea.

The project will initially construct a database of ash optical properties (extinction coefficient, single scatter albedo and phase function) based on existing information in the scientific literature and new ash measurements. These properties will then form the basis of an optimal estimation type retrieval of ash composition, optical thickness and effective radius from high resolution infrared spectra. The retrieval algorithm will be developed for three different types of observation:

1) High resolution infrared transmission spectra of ash near the volcanic vent. These spectra are provided by our project partners who will assist in the interpretation of the measurements.

2) High resolution infrared emission spectra from the Infrared Atmospheric Sounding Interferometer (IASI) onboard MetOp satellite. IASI is a nadir viewing Fourier transform spectrometer that covers the spectral range 645 to 2760 cm-1 (3.62-15.5 microns). The IASI field of view consists of four circles of 20 km diameter inside a square of 50 x 50 km, and nominally it can achieve global coverage in 12 hours.

3) High resolution infrared emission spectra from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard ENVISAT satellite. MIPAS measures atmospheric limb emission spectra from 685-2410 cm-1 (14.5 to 4.1 microns) over a tangent altitude range 6-68 km from 2002 to the present.

Using these instruments we will observe volcanic ash generated by several different volcanoes and during different stages of eruptive behaviour. The satellite based estimates of ash properties will be validated by comparing them to ash properties measured from ash samples as well as by comparison with other satellite results. Eruptions for which we have correlative measurements include Eyjafjallajökull, Grimsvötn, Nabro and Puyehue. The observed ash behaviour will then be interpreted in terms of the ash-generating volcanic processes.

WHO WILL BENEFIT FROM THE RESEARCH AND HOW?
An average of 845 people die each year as a consequence of volcanic eruptions. In addition there are considerable economic and social costs. For example, the eruption of Eyjafjallajökull in April 2010 resulted in the cancellation of 107,000 flights over Europe (or 48% of total air traffic) affecting roughly 10 million passengers. The airline industry lost an estimated £130 million a day during the 8 day period when European airspace was closed. Therefore the dissemination of the current state-of-the-art in volcano monitoring to stakeholders in Government and business is of crucial economic and social importance, both nationally and globally. Through its theme action plans NERC aspires to increase understanding of the spatial and temporal distribution of inherently unpredictable geohazard events to mitigate risks and support societal resilience. In quantifying the volcanic impact on the environment we have identified the following key beneficiaries:

i. Those at immediate risk from volcanic eruptions, i.e. those who live or work near a volcano.

ii. Volcanologists, climatologists and atmospheric chemists within the UK and internationally through the availability of quantitative estimates of atmospheric ash.

iii. The UK MetOffice, as improved measurements of volcanic ash will provide a stringent test of the MetOffice's NAME model.

iv. Air passengers, as improvements to NAME will feed through to provide better forecast of volcanic hazards during future eruptions.

v. The international atmospheric modelling community through the provision of well-validated ash measurements.

vi. The international volcanological community through the development of a new product to detect, measure and monitor volcanic activity. In the past five years, there has been at least one eruption each year which has been detected first by satellite remote sensing of the gas and aerosol emissions. This new work will extend this capability.

SHIVA will deliver a better ash-monitoring tool, as well as the best measurements to date of global volcanic ash emissions. The data will be available to the climate change, hazard monitoring, respiratory health and research communities, and thus will be an important factor in the formulation of advice to policy makers and the public.