On October 3, 1983, Mt. Oyama on Izu Miyakejima Island erupted after an interval of 21 years, causing a fissure-type eruption in a line from the middle of the mountain's southwest slope to the Nippana coastline and a magmatophreatic explosion in the vicinity of the coast.

Examples of the damages suffered include the destruction of 530 houses by fire in the village of Ako caused from magma flows, extensive damage to forests caused by the magma flows and falling ash, the destruction of Shinmyouike pond near the coast as a result of magmatophreatic explosions, and the destruction of many farm crops by falling volcanic rocks and falling ash. Fortunately the eruption did not result directly in the loss of any human lives.

Because the magma flows and large quantities of volcanic ash were distributed within a narrow range and there was no difference between the distribution area of the ejecta and the form of accumulation, it was possible to classify this damage according to the quantity of falling ash. We decided that this eruption offered better analytical possibilities than other cases, however, and determined the quantitative distribution of the ejecta by using LANDSAT/MSS data before (1980/11/11) and after (1983/10/25) the eruption.

The analytical method is shown as a flow chart in the appendix, but the unique characteristics of the method are described below.

1) Using the MSS images taken at two different times, we made a brightness correction to match the brightness of areas (training areas) for which we could judge there were no changes over time.

2) We then created a contrast image from the two brightness-corrected images, and based on this image examined the spectral characteristics of each area.

3) Taking the spectral characteristics into consideration, we created a volcanic ejecta distribution image by selecting and classifying the maximum likelihood method training areas.

4) We then compared the image with the field survey results, added quantitative judgments to the distribution image, and mapped the results.

When we selected the distribution areas of volcanic ejecta from the 1983 Miyake Island eruption and made a rough quantitative classification using LANDSAT/MSS data from before and after the eruption in 1983, we achieved results consistent with the distribution of magma flows, scoria and ash falls obtained from field surveys immediately after the eruption.

For investigations of extremely dangerous volcano disasters where the volcanic smoke reaches as far as several dozen kilometers, the analysis of satellite data is both indispensable and highly effective.

This approach is thought to have been particularly well suited for the eruption of Miyakejima Island in 2000.