"Vulkane am Äquator " (handout SS 2004) - hoststar

were still uninhabited when the first scientific mission arrived in 1790. The first eruption was
recorded near the end of that century and the first resident settled in 1807. The Chilean
islands were discovered, by Juan Fernandez in 1574, but no eruptions were recorded by
their only early resident, Robinson Crusoe, during his 1704-09 visit: it remained for Charles
Darwin to document the first (and only) historical eruption there in 1835.
Recent volcanic activities
Two volcanic crises in Ecuador beginning in September 1999 presented serious challenges
to scientists monitoring them and to many of thousands of people living nearby. Eruptive
activity at Volcán Guagua Pichincha, just west of the capital city of Quito (pop. 1.8
million), increased significantly in mid 1999, and Volcán Tungurahua (about 100 km south
of Quito) began to erupt in mid-September. By early October, both volcanoes were erupting,
and explosions, ashfalls, and mudflows began to affect areas nearby and downwind.
Guagua Pichincha
Location: 0.17 S, 78.60 W
Elevation: 4784 m
after
before
Pichincha, 7. October 1999. Ash column arises above Guagua Pichincha volcano, Ecuador,
minutes after an explosive eruption began in the summit crater (not visible from this view). The
column rose to a height of about 16.5 km above sea level. Ash fell in Quito soon after, forming a
layer 1-3 mm thick in northern parts of the capital city. This explosion and a similar one two days
earlier blasted away part of the volcano's summit lava dome and sent pyroclastic flows 4-5 km down
the volcano's west flank. During the month of October, 53 explosions sent smaller columns of ash
into the atmosphere, nearly double the number of explosions during previous months.
Guagua Pichincha is a stratovolcano which is located just 13 kilometers (~8 miles) west of
Quito, the capital of Ecuador. The volcano had minor eruptions in 1981, 1982, 1997, and
1998 but the last major eruption occurred in 1660 when the city of Quito was blanketed with
30 centimeters (~1 foot) of ash. On the afternoon of October 5, 1999, Guagua Pichincha
erupted sending large amounts of ash over and onto Quito. The ash caused severe air
quality problems and forced the closing of all commercial airports in and around the city.
Two days later the volcano erupted again, this time in the morning.
During most of 1999, activity at Guagua Pichincha consisted of many steam-driven explosive
eruptions and visible steam plumes that rose tens to hundreds of meters above the dome.
The magma added new material to the existing lava dome and led to stronger explosive
activity and a few pyroclastic flows. In November and December, the growing dome
produced more explosions, lava extrusions, and many rockfalls.
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