Geology 309 - Lecture 1
Introduction to Volcanology
Lets start with some cool images of the Earth:
Topography of the Earth
Global topography of the seafloor
Digital relief map of Washington State
Here are some links to get you familiar with volcanoes of the world (i.e.,
this is your homework reading):
Definitions
- What is a volcano?
- Requirements for volcanism
Why is volcanism important?
at least 4 reasons
Three classification schemes for Volcanoes
I. Eruption History (active, extinct, erupting, dormant)
II. Characteristic Eruption Style (see below - we'll talk about
this on 1/8)
III. Landforms
Characteristic eruption styles
Abridged from
R.V. Fisher's Volcanic Activity webpage.
-
Icelandic
- Hawaiian - consist of
basaltic, highly fluid lavas of low gas content,
that produce effusive lava flows and
some pyroclastic debris. Thin, fluid lava flows can gradually build up large
broad shield volcanoes. Most Hawaiian
eruptions start from fissures, commonly beginning as a line of lava
fountains that eventually concentrate at one or
more central vents. Most of the vesiculating lava falls back in a still
molten condition, coalesces and moves away as
lava flows. If fountains are weak, most lava will quietly well out of the
ground and move away from a vent as a lava
flow. Much lava in shield volcanoes is transmitted through tubes enclosed
within lava flows.
- Strombolian - named after Stromboli Volcano, Italy, are discrete
explosions separated by periods of
less than a second to several hours. They give rise to ash columns and
abundant ballistic debris. Ejecta consist of
bombs, scoriaceous lapilli and ash. Stromboli, and other Italian volcanoes
are described in Boris Behncke's page on Stromboli.
- Vulcanian - Vulcanian eruptions are more explosive eruptions
in basaltic to andesitic volcanoes that commonly arise from
hydrovolcanic processes. Many volcanologists
use the term Vulcanian for highly explosive, short-lived eruptions that
produce black, ash- and steam-laden
eruption columns as witnessed during the 1888-90 eruptions of Vulcano, a
small volcano in the Eolian Islands,
Italy
- Pelean
- Plinian - Widely dispersed sheets of pumice and ash are derived
from high eruption columns that result from high-velocity
voluminous gas-rich eruptions, commonly lasting for several hours to about
four days. These are called Plinian
from
Pliny the Younger who described the famous 3-day eruption of Vesuvius
in 79 AD during which the towns of
Pompei and Herculaneum were buried by several meters of pyroclastic material
from Vesuvius. Plinian eruptions
commonly produce high eruption columns. The energy and characteristics of a
Plinian eruption depends on gas
content of the magma, exit pressure, viscosity, vent radius and shape, and
volume of magma erupted. Most Plinian
eruptions result from explosions of highly evolved rhyolitic to dacitic,
trachytic and phonolitic magmas with
temperatures from about 750 to 1000 Celsius.
Many volcanoes exhibit more than one classic eruptive "style". For
example, Mt St. Helens eruption in 1980 included more than one kind
of eruptive behavior and more than one kind of volcanic hazard.
