# **6 Volcano Damage Index**

A volcanic eruption consists of ash clouds, pyroclastic flows and lava flows, the latter two which are very difficult to model without extensive local data. Unfortunately, there is little to no academic research that has looked into large scale volcanic modeling for all aspects of eruptions. For modeling ash clouds, Joyce _et al._ (2009) points to remote sensing through satellite images that detect SO2 emissions as a potential method.

To construct a damage index for eruptions, we use a two-fold process. First, volcanic ash advisory data are used from Volcanic Ash Advisory Centers (VAAC) to detect eruptions; second, satellite images containing sulphur dioxide data from the OMI/AURA satellite are used to model the intensity of the eruptions. The OMI/AURA images have been utilized by Carn _et al._ (2009) and Ferguson _et al._ (2010) to model eruption intensity.

## **6.1 Volcano Modeling**

There are at least two types of software that are used to model eruptions. Voris (Felpeto _et al._ , 2007), which models ash clouds, lava flows and energy cones, and HYSPLIT from Air Resources Laboratory, which models air pollution dispersion. Voris relies on highly localized data due to the lava flow and energy cone modeling, which one will not have in most cases and that does not fit well for large scale modeling across time and space. HYSPLIT does have batch inputs, but still requires several inputs per eruption, some which are not easily obtainable.

The third solution, which is related to the ash clouds mentioned by Joyce _et al._ (2009), is based off ash advisory data to determine whether an eruption happened and OMI/AURA satellite data to determine the scale of the eruption. This will not help with modeling lava flows and energy cones, but due to the very localized nature of the flows, there are no good sources or methods to model it for several eruptions from different volcanoes, leaving the ash clouds as a good proxy for all damages.

### **6.1.1 Ash advisory data**

Ash advisories from the Darwin VAAC (DVAAC), which are ash cloud warnings for airplanes, are used to determine whether an eruption is happening. The warnings show relevant data such as volcano name, position, summit height, height of clouds and a color code that reflects the condition of the air/volcano. There are 4 different codes ranking from the normal state, green, to imminent danger of or ongoing volcanic eruption, red. Over the period from 2004 until 2015, the DVAAC issued 12,962 warnings and of these more than 90 percent were either of code red or orange. Data on advisories from code orange or below were not used, due to eruptions of this scale not being large enough to be properly captured by the SO2-data. By limiting the data to code red events, there are 1,785 events spread across 587 dates.<sup>13</sup>

### **6.1.2 OMI/AURA Satellite images**

To measure the intensity of an eruption, data from the Sulphur Dioxide images of the OMI/Aura project (Krotkov & Li, 2006) are used. These consist of satellite images from October 2004 and onwards. The data have been used to model ash cloud intensity and movement in several articles such as Carn _et al._ (2009) and Ferguson _et al._ (2010).

The satellite images have a spatial resolution of 13 _∗_ 24km and are taken from 80km above ground. The spectral imaging shows the SO2 vertical column density in Dobson Units and there are 14 or 15 orbits per day, where one orbit covers an area approximately 2,600km wide. A dobson unit is a measure of density, and at sea level the typical concentration in clean air is less than 0.2DU. The images contain 4 values for column density based on the center of mass altitude (CMA), which is a measure of the altitude one assumes the center of the distribution is at. There are 4 different estimates for the vertical column density, ranging from 0.9km above ground to 18km above ground.

> 13There were 571 different dates, but some of these dates issued red warnings to 2 or more volcanoes.

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