Unformatted text preview: • !"#$%&'(")&*"+,-.)&"/&,01&2$0/#%3!!"#!$%!&'!('&)*+!,'%%$-(*!#'!
#+$,!'&!#0*!123!3'5!02>*!%$)&*1!5,!4'+7! • !"#$%4(")& – (*2>*%!2#!?!,@!'&!#0*!AB#[email protected]!'&!#0*!?%#!
– -5%*%!.$((!-*!$&!4+'&#!'[email protected]$(#'&!E2((!
• <;"=&>!2>2$(2-(*!4+'@!H+$123C!;*,#7AB#0!2#[email protected]!5&N(!
2&1!#'!,+*%%!#0*!;:M9"<!-5='&!.0*&!6&$%0*1W! Exploding Earth: volcanoes 1. Introduction
3. Location of Volcanic
4. Types of Lava
5. Types of Volcanoes
6. Volcanic Hazards
7. Volcanic Rocks
http://volcanoes.usgs.gov/ • !! April 2010
• Eruption ofer second of ash
• T%0!,([email protected]*!1$%+5,#*1!
4'+!%*>*+2(!.**Y%! Mt. St. Helens http://vulcan.wr.usgs.gov
Erupted in 1980: recent activity 2004-2006 (but on-going) • Ongoing earthquake
• Movement of magmaolcano the
v Sept 2004 Sept 2005 lots of small earthquakes near the surface growth of lava dome - 2005 Why is it important to understand
how volcanoes work?
– To understand/predict volcanic hazards # killed Laki (1783), Iceland >10000 Mt Pelee ( 1902), Martinique >30000 Mt St. Helens ( )
Nevado del Ruis ( ), Columbia
Montserrat ( ), Martinique 62
19 - To understand the nature of earth's interior
- Resource exploration (rare gems are related to
volcanic activity) - Geothermal NRG
- New Zealand, Iceland, Canada (BC) produces
it • MAGMA: Molten Rock • LAVA: magma that reaches the earth's surface • Pyroclastic degree: lava and rock
fragments ejected during a volcanic
l ava) Lapilli - small ball of lava (smaller
than a dime) Ancient Volcanic Ash layers - can cause health issues b/c
ash is so small you cant tell what it is • • VENTS - opening through
which eruption takes place VOLCANO - hill or mountain
produced by volcanism • Crater - • depression over vent CALDERA - depression; > 1 km wide Where do we find volcanoes?
• D IVERGENT PLATE BOUNDARIES (plates pulling apart)
- ex: submarine eruptions along mid-oceanic ridge, Iceland Fig. 2.1 Pillow lavas when lava comes up and
cools quickly Convergent plate boundaries (plates subducting under each other) ! Fig. 7.22 - Paciﬁc "ring of ﬁre"
- Mt. Pinatubo
- Cascade Volcanoes
(mt. st. Helens) • HOT SPOTS - not associated with plate boundaries
(ex: Hawaii) Fig. 2.39 • Related to mantle
columns of hot
• Plume is stationary, plates
move Chain of
• produced -volcanic islandson
the sides Fig. 2.42 Which is the
Guyots are old volcanic islands under the waters surface e.g. Hawaiian islands Fig. 2.43
- Youngest Hawaiian Island
b/c its the biggest, all other
- eroding by wave action to
form seamounts Fig. 2.36 Why do hot spots develop in certain places?
- Hot Spots related to mantle plumes
- Hawaii - over plume - rocks have isotopic characteristic of core Silica content of magma is critical • Affect style of eruption and
type of volcano produced
– • Silica rich (felsic) lavas - Very viscous, ﬂow slowly
- gases cannot escape easily
- violent eruptions, explosive
- ex: rhyolite • Silica-poor (maﬁc) lavas - low viscosity, ﬂow easy
- gases escape easily
- quiet eruptions, lava ﬂows
- Basalt • Intermediate lavas (ex: andesite) • 3 main types - shield, conder cone, composite - Shield Volcanoes: broad, sloping cones, low
viscosity lava ﬂows, non-violent eruptions
(maﬁc) e.g. Hawaiian Islands Pahoehoe - ropey (hot lava) • Basaltic lavas flow easily • Two types
– - Pahoehoe
- Aa Aa - sharp, jagged (cooler) Form on shield volcanoes
• Splatter cones: trapped in cooling lava
when gas is Apillie, pyroclastic cones build up and you get a little cone volcano • Pyroclastic Cones: made of pyroclastic debris;
steep slopes; small
- Felsic or intermediate lavas
- formed when gas escapes
- ex: Sunset Crater, Arizona • COMPOSITE VOLCANOES - alternating lava
ﬂows and pyroclastic debris
- intermediate steepness
- form over a long time
- can be very large e.g. Mt. Garibaldi, B.C.
Fig. 7.21 • - m ostly associated with intermediate
lavas (andesitic), violent eruptions
ex. Mt. St. Helens,
Mt. Etna, Mt.
Vesuvius Table 7.2 What kinds of hazard are produced by volcanoes? • Lava Flows -- destructive to
property, roads, etc Pyroclastic debris
- volcanic bombs, ash pyro --> Fire
clastic --> broken Mt. St. Helens's -- volcanic ash microscopic
ash ASH - tiny glass shards • PYROCLASTIC FLOWS - nuee ardente, mixture of
hot gases and volcanic debris
- tavels at >100km/h
- very dangerous
- St. Pierre, Martinique, 1922 Mayon Volcano, Phillipines, 1984
ﬂow of hot gas/ashes • Debris ﬂows
- mudﬂows, ﬂow along valleys - hot mud ﬂows 1985 eruption:
Lahars caused 23,000 deaths TOXIC GASES
- Water vapour, CO2, CO, hydrogen
sulphide, sulphur dioxide
- heavier than air
move along topographic depression Lake Nyos, Cameroon
August 21, 1986
1700 people killed by CO2 • Steam explosions
–- seawater seeps into rock and comes into contact with magma
- steam produced and blows up volcano
(phreatic eruption) e.g. Krakatoa, 1883
silica is sticky; traps gas, causes
l arge explosion • Krakatoa (1883)
– sound heard 3000 miles away
– 40 m high tsunami killed over 36,000 people
– huge ash clouds produced
) What is the effect of huge ash clouds - l ower temp
- effects on climate
- global temperature reduced 0.5'C for 10 yrs
after Krakatoa eruption, cooling after Pinatubo ? What is a rock?
a ROCK is a naturally
• material composed of formed,ofconsolidated
one or more
m inerals What is a mineral
• a MINERAL is a naturally occuring,
inorganic, crystalline solid that has a
deﬁnite chemical composition Volcanic Rocks
also called igneous rocks
• - -form from solidiﬁed magma volcanic plug;
away • either at the Earth's surface (extrusive) or underground (intrusive) How do we classify igneous rocks?
by Texture (coarse and ﬁne) by mineralogy (composition of magma) Intrusive Igneous rocks
Under what conditions would these form?
How would this affect their characteristics?
• Cool slowly ( > 1 million years), under pressure • - Coarse grained (large crystals) - granite (quartz, feldspars)
- Gabbro (Ferromagnetism, feldspars) gabbro granite INTRUSIVE IGNEOUS ROCKS
- formed at depth are called plutonic rocks • INTRUSIONS - bodies of
i nstrusive rock - plutons, sills,
dykes Fig. 6.2 e.g. Ship Rock, New Mexico Fig. 6.8 DIKES Extrusive Igneous Rocks
How do these differ from intrusive igneous rocks?
• Cool rapidly as lavas or tephra (rock fragments) Mostly ﬁne-grained (small crystals) intrusive extrusive EXTRUSIVE
_______________ Intrusive igneous rocks • Either Silica rich, light coloured (ex. rhyolite) • Or rich in ferromagnetism minerals, dark coloured (ex. basalt) basalt rhyolite Extrusive Igneous Rocks • may be glassy (ex: osidian)
- extremely rapid
cooling • may contain vesicles, or holes
(ex: pumice) Can rocks float? Yes – if they are pumice! • Read Chapters 6 and 7 in textbook
– Igneous rocks, intrusive activity
– Volcanism and extrusive rocks • Answer this question:
What are phenocrysts? ...
View Full Document
- Fall '11
- Volcanology, Igneous rocks, Volcano, intrusive igneous rocks, Extrusive Igneous Rocks, Volcanic rocks