Slide set compiled by Rick Holasek, University of Hawaii
PINATUBO ERUPTION CLOUD, JUNE 15, 1991
Rick Holasek gratefully acknowledges the assistance of Fred Prata and CSIRO (Commonwealth
Scientific and Industrial Research Organisation) in Melbourne Australia for help obtaining the GMS
data.
These are a part of Rick Holasek's Ph.D. thesis, and some of it is in press in the paper
by S. Self, J.-X. Zhao, R.E. Holasek, R.C. Torres, and A.J. King, The atmospheric impact of the
1991 Mount Pinatubo Eruption, part of a USGS Professional Paper edited by R.S. Punongbayan and
C.G. Newhall, The 1991-1992 eruptions of Mount Pinatubo, Philippines.
Definitions
Column: Vertically rising volcanic ash and gas.
Plume: Horizontally moving volcanic ash and gas.
GMS Visible Images (0.5-0.75 micrometers wavelength, 1.25 km spatial resolution)
1331
Philippine Local Time (244K image size)
This image shows the beginning of the 3 hour long climactic eruption. The overshooting plume
top in the center casts a shadow onto the main plume. The yellow X is the approximate location of
the vent.
1431
Philippine Local Time (253K image size)
This image shows the climactic eruption approximately 1 1/4 hours after it started. The
overshooting plume top in the center casts a shadow onto the main plume. The yellow X is the
approximate location of the vent.
1531
Philippine Local Time (241K image size)
This image shows the climactic eruption approximately 2 1/4 hours after it started. The
overshooting plume top in the center casts a shadow onto the main plume. Note the westward
direction of the wind carrying ash at the altitude of the overshooting plume top, in contrast to
the SW movement of the prevailing winds lower in the plume, where the majority of the wind-blown
ash is being carried by the maximum atmospheric wind speeds at the tropopause. The yellow X is the
approximate location of the vent.
1631
Philippine Local Time (223K image size)
This image shows the climactic eruption approximately 3 1/4 hours after it started. The
overshooting plume top in the center casts a shadow onto the main plume. Note the westward
direction of the wind carrying ash at the altitude of the overshooting plume top, in contrast to
the SW movement of the prevailing winds lower in the plume, where the majority of the wind-blown
ash is being carried by the maximum atmospheric wind speeds at the tropopause. The yellow X is the
approximate location of the vent.
1834 Philippine Local Time: 2D contour plot (134K image
size)
This shows the different temperature levels within the giant umbrella plume. The temperature
scale is in the lower right hand corner of the image. Temperature increases towards the center of
the plume because it is getting higher in the stratosphere and therefore warmer. Comparisons of
plume-top temperatures with ancillary data on atmospheric temperatures indicates the plume reached
a maximum altitude of 34 km in this image. The cold region at the rising center of the column is
due to plume undercooling. The buoyantly rising column overshot its level of neutral buoyancy and
became undercooled due to rapid decompression. The black + is the location of the vent.
1834 Philippine Local Time: 3D plot (28K image size)
This three-dimensional representation shows the plume dimensions as rows and columns on the y
and x axis, respectively. The z-axis shows the relative temperature in Digital Numbers (DN).
Higher values are warmer (i.e., red) and lower values are colder (i.e., blue). Note the hot
thermal "spike" in the center of the plume and the trailing green ridge. This is due to
the great altitude reached by the overshooting central portion of the plume reaching high into the
stratosphere (35-40 km) and warming significantly as a result. The trailing green ridge is the
downwind ash blowing off the overshooting plume top at a high stratospheric level (ash shown in
the GMS visible images above). The temperature of the ambient stratosphere exhibits a upwardly
warming trend, and therefore the plume gets warmer as it reaches greater altitudes.
Series of four images showing the different temperature levels of the plume-top as different
color intervals. The color bar in the lower right hand corner delineates the different temperature
levels. The red X shows the approximate location of the vent. Maximum altitude determined from
comparing the plume-top temperature with ancillary data on atmospheric temperatures allowed us to
determine a maximum altitude of 37 km at 1531 Philippine Local Time.