Download Types of volcanic activity Volcanoes over

Lecture 16:
VOLCANOES
LOCATIONS OF ACTIVE VOLCANOES
Geog 1000 Introduction to Physical Geography Fall 2013 : Dr. Hester Jiskoot, University of Lethbridge
Types of volcanic activity
Volcanoes over subduction zone
Volcanic activity on top of deeply subducted oceanic plates
Volcanism
Crust destroyed
Effusive eruptions: Sheet volcanoes
Common in Hawaii and Iceland
Æ lavaflows
Effusive eruptions
(gentle flows, lots of lava)
• cinder cones
• shield volcanoes
• plateau basalts
Explosive eruptions
(viscous lava, trapped gases)
• composite volcanoes
• calderas
Explosive eruptions: Composite volcanoes
or ‘Stratovolcanoes’
Æ Ashes
Kilauea, Hawaii
Fujiyama, Japan
Crater Peak vent (beneath clouds),
Mount Spurr, Alaska
USGS
Typical composite volcano
Shield/Composite Comparison
Pyroclastics
COMPOSITE VOLCANO (Mt Jefferson)
Above present subduction zone
Most recent eruption was in 950 AD
A RANGE OF LAVA
TYPES ARE DEPOSITED
BY A VOLCANO
Æ Due to cooling and
crystallisation and changing
the lava composition
PLATEAU BASALT
from longterm effusive mantle plume activity (SHIELD VOLCANOES)
Bulk of basalt from 17–14 million years ago
Cove Pallisades Park, Oregon, Aug 2010
Eruption column up to 18 km asl
“Volcanic bomb”
PYROCLASTICS
IGNEOUS ROCKS
- can be classified under
the following criteria.
• Extrusive/Volcanic
• Instrusive/Plutonic
• Texture/crystal size
Obsidian
(volcanic glass)
Portland
• Chemical composition
Caldera = a crater lake
Dacite volcanic bomb
and pumice
Mt St Helens
Basalt lava
Hawai’i
Mazama Ash at Fish Creek, Calgary
~7700 yrs ago
Dated 7700 y B.P.
Mount Mazama
erupted and
magma chamber
collapsed
Mount Mazama NOWÆ Caldera: Crater Lake, Oregon
Photo by G. Osborn
VOLCANIC ERUPTION UNDER ICE CAP
Geyser in Iceland
Geysers form when underground
chambers fill with water and are
heated geothermally.
When the water reaches its boiling
point, the geyser erupts and the
cycle starts again.
Grimsvötn, Iceland eruption 1-4 Nov 2004
Volcanic Hazards and Effects
•
•
•
•
•
•
•
hot ash (pyroclastics)
steam and gas explosions
lava flows
poisonous gases (carbon dioxide, sulfuric acid)
landslides
tree blowdowns
lahars (steam-melted ice and snow cause flooding
and large mudflows)
Benefits of Volcanic Eruptions
• New, fertile soils
– Hawaii, Philippines, Indonesia, Andes
• Geothermal energy
– Iceland, Italy, New Zealand
• New ‘Real Estate’
– Iceland, Japan, Hawaii
• New Rocks & Minerals
– Diamonds are NOT forever
• increase in atmospheric dust
2010
Mt. VESUVIUS eruptions
e.g. 79 AD: Pompeii
1631 AD: Naples
Eyjafjallajökull, Iceland
BIGGEST 20th CENTURY
ERUPTION
0.14 (0.03)
MOUNT PINATUBO
Philippines
15 June 1991
Earthquakes Æ warning
Population of 500000 in area
5000 people evacuated from
10 km radius around crater
>800 people died, mostly
from roof collapses
Cooled Earth by 0.6º C in the
following year
Mount St. Helens: The Day Before
1980 Mt St Helens Eruption
Oct 2004 renewed activity
Some volcanic ash (tephra)
plumes since
the last Ice Age
Glacier Peak
B
11,250 yr BP
G
12,750 yr BP
Mazama
7,700 yr BP
Mt St Helens
Y
3,500 yr PB
Modern 1980 AD
http://www.geo.arizona.edu/palynology/geos462/15volctephra.html
Eyjafjallajökull eruption, Iceland, April-June 2010
Ash plume disrupted air travel in NW
Europe for 6 days in April and some
days in May
Volcanoes & Climate –
the “haze” and “albedo” effects
For volcanic eruptions in past 400 yrs:
• Few tens of °C winter warming immediately following
eruption
• Few tens of °C summer cooling for up to 2 yrs after a
major eruption
• Disruption of El Niñ
Niño & North Atlantic Oscillation
patterns
• Uneven global distribution of effects
• Climate effect smaller than natural variation
http://volcano.si.edu/reports_weekly.cfm
Reading for next week
Monday
Chapter 10
Weathering, karst Landscapes and Mass Movement