Analysis of volcanic clouds

Mt. Cleveland Volcano is located in the Island of Four Mountains in the central Aleutian Islands, Alaska. The volcano erupted explosively on 19 February 2001 for at least 8 hours.  The eruption was detected as part of the AVO project at UAF. The 19 February eruption was the largest of three eruptions of this volcano over a 30 day period, resulting in a volcanic cloud that formed an arc over 1,000 km long, moved to the NE across Alaska and tracked using satellite data over more than a 50 hr period. The ash cloud was detected on satellite data from the three primary satellites used for volcano monitoring at this time.  These are; Geostationary Operational Environmental Satellite (GOES), Very High Resolution Radiometer (AVHRR), and the Moderate Resolution Imaging Spectrometer (MODIS). The ash cloud seriously disrupted air traffic in the region.

Time-sequential composite of GOES Images showing the ash as it moved across Alaska.  The image was processed using the reverse absorption technique to detect ash.  White lines show air traffic routes in the region.

Images: (right) The volcano erupted into a complex wind field resulting in a somewhat usual, arc-shaped structure of the ash cloud. A GOES TIR satellite image shows atmospheric conditions, including divergent jets and low pressure cells that resulted in an atmospheric trough at the volcano when the eruption occurred.

An important component of volcanic cloud analysis is estimation of cloud-top height. Atmospheric profiles of temperature and wind fields are used in conjunction with TIR satellite data to make these estimates. The AVHRR satellite image (below left) is a composite of the TIR (B 4, 10-11 micron) data that detects temperature and the reverse absorption technique to detect airborne volcanic ash.  The opaque cloud located NW of the volcano has a temperature is -53°C and correlates to an altitude of approximately 8km shown on the vertical atmospheric-temperature profile (below right).  The wind fields indicate a wind shear at about 6 km.  Any material above 6km would blow to the NW (the opaque cloud) and below 6 km to the SE (the ash cloud).