III. Volcanic Deposits

1
Introduction to Volcanoes
III. Volcanic Deposits A. Lava effusive
deposits Non-explosive 1. Basalt 2. Andesitic
Lava B. Pyrolcastic deposits Explosive
deposits 1. Andesitic 2. Rhyolitic Viscous it
tends to cool underground or explode violently.
2
09_16a.jpg
3
Introduction to Volcanoes
3. Pyroclastic Flows (nuée ardente) French for
glowing cloud or glowing avalanches Airborne
material that rushes down the sides of a
volcano. Floats on a layer of trapped air and
magmatic gases, so remains buoyant. Speeds
exceeding 100 miles per hour, even on flat land
(up to 125 mph) Still hot when they stop
flowingfuse together to form welded tuff Welded
tuff solid form of tephra
III. Volcanic Deposits
4
Introduction to Volcanoes
Pyroclastic Flows (nuée ardente)
5
Introduction to Volcanoes
Pyroclastic Flows (nuée ardente)
6
Introduction to Volcanoes
Pyroclastic Flows (nuée ardente)
7
Pyroclastic flow High-speed avalanches of hot
ash, rock fragments, and gas move down the sides
of a volcano during explosive eruptions or when
the steep edge of a dome breaks apart and
collapses. These pyroclastic flows, which can
reach 800F and move at 100-150 mph, are capable
of knocking down and burning everything in their
paths.
8
Introduction to Volcanoes

• Factors controlling types of Volcanic Eruptions
• Viscosityresistance to flow
• Temperatureheat lowers viscosity (heating syrup)
• 2. Magma compositiondirectly related to silica
  contentchains even before crystallization begins
• B. Gases 1-9 of magma

• II. Types of Volcanic Eruptions
• Effusive (non-explosive) lava flows out fairly
  easily
• a. Lava (basalt, andesite)
• 2. Explosive / Pyroclastic
• a. pyroclastic deposits w/ different types of
  Tephra
• 3. Lahars volcanic mud flows

9
(No Transcript)
10
09_05c.jpg
11
09_05d.jpg
12
09_05e.jpg
13
09_06a.jpg
14
09_06b.jpg
15
09_06c.jpg
16
09_07a.jpg
17
Question of the week
1. What two factors control the types of volcanic
eruptions?
18
Introduction to Volcanoes
III. Volcanic deposits C. Lahars Indonesian
for mudflow. Volcanic debris become saturated
with water, massive mudflows Form and race down
valleys (usually follow gullies and stream
valleys) Water from snow melting, or rain after
a volcano erupts (can happen after the
eruption) Consists of debris to ash to 100-ton
boulders Travels tens of kilometers per hour.
19

• W. W. Norton

20
Introduction to Volcanoes
21
Introduction to Volcanoes
III. Volcanic deposits C. Lahars Mt St Helens,
water was 4 meters above flood stagenot so
populated (killed 6 people) Deposited 3.4
million kg of debris into Columbia River. Ships
couldnt navigate for a week
22
(No Transcript)
23
(No Transcript)
24
Introduction to Volcanoes
III. Volcanic deposits C. Lahars 1985 Nevado
del Ruiz in Andes Armero, Columbia--lahar
killed 23,000 people. Río Lagunillas, former
location of Armero.
Within four hours of the beginning of the
eruption, lahars had traveled 100 km and left
behind a wake of destruction more than 23,000
people killed, about 5,000 injured, and more than
5,000 homes destroyed along the Chinchiná, Gualí,
and Lagunillas rivers.
25
On September 13, 1985, Nevado del Ruiz released a
lahar triggered by a glacial outburst from a
small eruption the previous day. This lahar
traveled at a speed of 10-30 km/hr down the
Azufrado River valley and buried the town of
Armero and approximately 24,000 of its residence
before they knew what was happening. These lahars
almost exactly matched previous lahar deposits
from 1595 and 1845.
26
Mt. Rainier Dormant volcano whose glacial load
exceeds that of any other volcano in the
coterminous US. 4393 meters, 14410 feet to the
summit of Mt. Rainier
27
Lahars, along Mt. Rainer, pose the greatest
volcano hazard in the Cascades Range. Hazards
from tephra and pyroclastic flows relatively
minimal. The number of pyroclastic deposits
relatively small, probably because they are
converted to lahar-type deposits as they flow
over the abundant glaciers and snow-fields.
28
5700 years ago, the Osceola mudflow originated
from the summit of Rainier. Largest known
lahar from Mt. Rainier (past 10 ka). Began when
part of the volcano collapsed, turned into a
lahar or mudflow. It was the product of a large
debris avalanche composed mostly of
hydrothermally-altered material, and may have
been triggered as magma forced its way into the
volcano. Covers an area of 550 sq km or 212 sq
miles. Extends all the way to Puget Sound
29
If this mudflow moved as quickly as one that
happened in Columbia about 10 years ago, it would
have been emplaced within 3 hours. Osceola
deposits extend at least as far as the Seattle
suburb of Kent, and to Commencement Bay, now the
site of the Port of Tacoma. Region now home to
many people in Buckley, Enumclaw, Pacific,
Auburn, etc.
30
Schematic diagram of a strato volcano,
illustrating the different layers of different
materials that comprise them. The purple colors
represent ash layers, either the products of
fall-out from big eruption clouds or the products
of pyroclastic flows. These ash layers are thin
but widespread. The orange colors represent
lava flows, and note that some of them have
cinder cones associated with them at the vent.
31
Electron Lahar Occurred about 600 years ago,
and has not been correlated with an eruption.
More than 30 m (100 feet deep). Made it all
of the way to Puget Sound.
32
Risk- more than 100,000 people live on lahars
associated with Mt. Rainier. The risk that a
structure will be affected by a lahar is about
the same as by a fire. Frequency of lahars
about 1 every 500 years.   May not have advance
warning!
33
III. Volcanoes D. Gases(volatiles)held in
magma by confining pressure, when pressure drops
then gases escape. Gases from within the Earth
- volcanoes provide an escape mechanism Gases
that come out of volcanoes greatly influence the
composition of our atmosphere 1-9 of total
weight of magma 70 water 15 CO2 5 N2 5 SO2 5
Cl2, H2 and Ar
34
Environmental Geoscience

• SO2 gas can be especially nasty
• In the atmosphere it combines with water vapor,
  producing H2SO4.
• This may remain suspended in the atmosphere for
  years producing acid rain.
• Increasing the acidity of local, regional and
  global waters

35
Environmental Geoscience
36

• When Mount Pinatubo erupted in the Philippines
  June 15, 1991, 20 million tons of sulfur
  dioxide and ash particles blasted more than 12
  miles (20 km) high into the atmosphere.
• Gases and solids injected into the stratosphere
  circled the globe for three weeks.
• Volcanic eruptions of this magnitude
• Impact global climate
• Reduce the amount of solar radiation reaching the
  Earth's surface
• Lower temperatures in the troposphere
• Change atmospheric circulation patterns

37
Climate change Gases injected up into the atm
(stratosphere-10-50km of atm) many remain for
years affect climate Large sulfuric-acid
droplets (aerosols) Reflects solar radiation
coming from sun back into space (also
absorbs) Lowers troposphere temp (0-10 km)
June 1991 Pinatubo eruption in Philippines
volcano lowered global temp 0.9?F
38
Climate change 1815 eruption of Indonesias
Tambora Year without a summer Unusually cold
spring and summer and an early fall (lowered temp
2-5?F) Caused shortened growing season and crop
failures - famine in some regions Snow in
upstate New York in June! Eruption caused two
days of darkness 400 miles around the
volcano. Ash column reached 43 km.
Spectacular sunsets inspired Byron - wrote the
poem Darkness Mary Shelley wrote a short story
that eventually led to her writing of
Frankenstein.
39
F in high quantities can be lethal to animals and
plants CO2 contributes to global warming although
volcanoes only contribute a small proportion to
this Volcanoes release 110 million tons of
carbon dioxide into the atmosphere Human
activities release 10 billion tons into the
atmosphere