Detection and analysis of the volcanic clouds associated with the 18 and 28 August 2000 eruptions of Miyakejima volcano, Japan

Two significant eruptions occurred at Miyakejima volcano on 18 and 28 August 2000 and were detected by multiple satellite sensors. For both eruptions, the cloud can be observed with high confidence for 2 days. Using Total Ozone Mapping Spectrometer (TOMS), MODerate resolution Infrared Spectroradiometer (MODIS), Advanced Very High Resolution Radiometer (AVHRR) and High Resolution Infra Red Radiation Sounder (HIRS) imagery, constraints are placed on the masses and distributions of ash and SO2 released by the eruptions. The 18 August eruption at 08:02 UTC (17:02 JST) emitted an ash cloud of at least 511kt and a sulfur dioxide (SO2) cloud of 43kt to a height of approximately 16km asl, which then drifted south. The 28 August eruption (19:35 UTC, 04:35 JST) was smaller, with a cloud containing a minimum of 0.2kt of ash and 21kt of SO2 at a height of 5km to the northeast of the volcano associated with a low-temperature pyroclastic surge. The 18 August eruption probably represents a vent-clearing phase, given the magmatic nature of the erupted products, the significant amounts of ash produced and the prodigious gas emission rates in the following passive degassing phase, while the 28 August eruption was mostly phreatic, with a cold-surge component not easily detectable by any of the sensors used. Comparisons of detection ability of the sensors were also made. The results suggest that the ultraviolet sensor TOMS more regularly detected SO2, as it is less susceptible to interference of water vapour and other species, as is observed with the infrared sensor MODIS. TOMS was able to detect SO2 for a total of 5 days for both eruptions combined, whereas HIRS detected SO2 for 3 days of the first eruption and MODIS detected the gas cloud for 1 day of each eruption. AVHRR was the most consistent when detecting ash and was able to see ash clouds not detected by the other sensors because of its more serendipitous overpass timing.