A view of the Santiaguito dome complex
as seen from the summit of Santa Maria. Coalescing domes have been growing for
90 years within the crater left by the catastrophic 1902 Santa Maria plinian
eruption (a 6 on the Volcanic Explosivity Index). Plinian eruptions have
columns of gas and volcanic ash that extend high into the stratosphere and
include such characteristics as ejections of large amounts of pumice and very
powerful continuous gas blast eruptions.
In January 2007, principal investigator
Jeffrey Johnson (with New Mexico Tech at the time) and a multi-institution team
of researchers conducted a week-long field experiment that included
establishing a manned observation post near the summit of Santa Maria from
which eruptions of Santiaguito's Caliente dome can be viewed.
Caliente (summit elevation ~2600 meters)
is located approximately 1.2 kilometers below and 2 kilometers to the southwest
of the Santa Maria summit. In recent years, Santiaguito has been simultaneously
extruding dacitic magma and erupts explosively several tens of times each day.
Typically these pyroclastic-laden eruptions originate from diffuse, often
concentric fractures distributed about the 200 meter-diameter crater. Plumes
are buoyantly driven up to heights of 1 to 2 kilometers. Larger explosions
and/or associated lava flow that collapse on the steep slopes of Caliente dome
generate pyroclastic flows that are generally confined to the upper reaches of
the volcano.
The project by Johnson and the team
included coordinated experiments on the volcano with seismic and acoustic
sensors (for analysis of earthquakes), infrared video (for study of thermal
signals), Doppler radar (for analysis of eruption material velocities), UV
absorption imagery (for analysis of gas flux), and high-resolution digital
video (from the summit looking straight down into the vent). Simultaneous
thermal and UV imagery was obtained from the Santiaguito Observatory.
Graduate student Richard Sanderson
enjoys the sunrise from the summit of Santa Maria. The shadow of Santa Maria is
overprinted on the Guatemala cordillera.
This research was supported in part by a
grant from the National Science Foundation's Division of Earth Sciences (EAR
04-40225). Johnson was with New Mexico Tech earth and environmental sciences
department at the time of this research but is now in the department of
geosciences, Boise State University. (Date of Images: 2007)
Credit: Professor Nick Varley, Facultade
de Ciencias, University of Colima, Mexico
Posts
No comments:
Post a Comment