The grayish volcanic tephra is unique to each eruption and can be identified microscopically.
To survey the main building types in the areas principally at risk and to assess their vulnerability to pyroclastic flow and tephra fall damage.
The only historical event (AD 1886) erupted 1.3 km3 of purely basaltic tephra fallout killing about 150 people.
Tephra analysis was carried out in order to observe possible isochrones, which were then used to form a relative chronology.
Initial results suggest a clear developmental sequence on the flows that have not been disturbed by tephra deposition.