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Chapter 6- Volcanoes. Which statement concerning volcanoes is accurate?. All volcanoes erupt explosively. Lava is the most deadly thing about volcanoes. Volcanic eruptions can influence the climate of Earth. Volcanoes occur in random locations on the surface of Earth. Volcanoes.

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which statement concerning volcanoes is accurate
Which statement concerning volcanoes is accurate?
  • All volcanoes erupt explosively.
  • Lava is the most deadly thing about volcanoes.
  • Volcanic eruptions can influence the climate of Earth.
  • Volcanoes occur in random locations on the surface of Earth.
slide3

Volcanoes

expulsion of molten rock (Lava), gases and

water vapor onto the surface of the Earth.

sometimes violently, sometimes not

-

1500 active volcanoes

>

Active = erupted in recorded history

-

e.g. Mauna Loa and Kilauea (Hawaii)

-

Mt. St. Helens (Washington)

-

Mt. Pinatubo (Philippines)

-

Mt. Fujiyama (Japan)

-

Mont Serrat (Caribbean)

Mt. Fujiyama, Japan

slide4

Dormant

Extinct Volcanoes

vs

Dormant volcanoes

Dormant volcanoes

-

have not erupted recently, but may do so again.

-

have not erupted recently, but may do

>

Mt. Vesuvius (Italy)

>

Mt. Vesuvius (Italy)

Extinct volcanoes

Extinct or inactive volcanoes

-

have not recently erupted

-

nor do they give indications

of erupting in the future.

Thousands of these

>

>

types ofvolcanoes exist.

Mt. Kilamanjaro (Tanzania,Africa)

what materials are not commonly associated with volcanic eruptions
What materials are not commonly associated with volcanic eruptions?
  • Lava
  • Steam
  • Gasses
  • All of the above are associated with volcanic eruptions
slide8

Discussion: Why do some volcanoes erupt explosively, whereas others erupt in a more subdued fashion that is not explosive?

Water in magma

more water = more explosive

Magma composition

high silica content = high viscosity (flow resistance)

high viscosity = more explosive

Magma Temperature

cooler = higher viscosity (see above)

Gas content

more gas = more explosive

All factors are related to tectonic location

slide9

a.k.a.- stratovolcanoes

-

interbedded pyroclastics and lavas.

-

typically andesitic to rhyolitic lava

>

intermediate to felsic magma composition

-

Found on continents and island arcs

>

mostly associated with convergent plate

boundaries (subductive)

>

examples of composite

Mt. St. Helens, Mt. Vesuvius, Mt.Pinatubo,

Mt. Fujiyama, Mt. Kilamanjaro., Mt. Rainier (photo)

Composite Volcanoes

slide11

Composite or Stratovolcanoes

Mayon volcano, Philippines, is a

Mayon volcano, Philippines, is a

View of Mount St. Helens,

View of Mount St. Helens,

nearly symmetrical composite

nearly symmetrical composite

Washington in 1978.

Washington in 1978.

volcano.

volcano.

slide12

Cinder Cones

Primarily cinder-sized (0.25-1.0 mm) material.

but may have other sizes too.

Cinders fall to Earth and collect around the vent.

have steep slopes up to 33 degrees

smaller than shield volcanoes, usually less than

400 m tall

Form on the flanks of larger volcanoes.

slide14

Lava Types

Pahoehoe lava (smooth & ropey) in

Aa lava (rough and blocky) also

Pahoehoe lava (smooth & ropey) in

Aa lava (rough and blocky) also

Hawaii.

in Hawaii.

Hawaii.

in Hawaii.

Lower viscosity lava

Higher viscosity lava

slide15

Pillow Lavas

These bulbous masses of pillow

These bulbous masses of pillow

lava formed when lava erupted &

lava formed when lava erupted &

cooled under water.

cooled under water.

1 meter

1 meter

slide16

Lava Fountain

Lava Fountain

slide19

Pyroclastic Ash Flow

'

aka Nuee Ardentes

aka Nuee Ardentes

Pyroclastic ash- lava blown up into the air

smaller stuff is ash, larger stuff are

called "bombs"

Pyroclastic Ash Flow

extremely fast (100's m/sec)

extremely hot

-

sometimes glowing redhot

extremely lethal

-

many deaths associated with volcanic

eruptions are related to these events

e.g., Pompeii and Herculanum

>

slide21

Pyroclastic flow

,

Nuee Ardente

slide23

,

Lahars & Nuee Ardentes

Lahars are mud flows that often occur after eruptions.

Nuée ardentes are mobile dense clouds of incandescent ash that can move downhill at

,

speeds up to 100 km/hr.

Mt Pelee destroyed St. Pierre on the island of Martinique, West Indies in 1902

slide24

The effects of explosive volcanic activity

Casts of people from Pompeii, killed by ash from Mt. Vesuvius, Italy

slide25

Gases and Magma

Volcanic gases

-

water vapor

- carbon dioxide

-

nitrogen

- sulfur oxides

-

hydrogen sulfide

- chlorine

Felsic magmas

-

highly viscous : Si-rich

-

inhibits the expansion of gases

-

pressure builds up

-

explosive eruptions, like Mt. St. Helens.

Mafic magmas

-

lower viscosity

-

lower gas pressure

-

erupt rather quietly, like Hawaiian Volcanoes.

slide26

Lake Nyos, a volcanic lake in Cameroon, Africa

CO2 emitted from the acidic lake killed 1700 villagers near the lake in 1986

slide32

Distribution of volcanoes is not random

related to plate tectonics

commonly found along plate boundaries

slide33

Effects of Volcanoes and their activity

builds up mountains and new land or destroys old

(geosphere)

-

kills many living things

(biosphere)

-

ejects ash and gases into the air

Changing weather and climate patterns for several

months to a year

(atmosphere)

-

Causes changes in drainage patterns, and pollutes

many water sources

(hydrosphere)

-

Ash blocks incoming sunlight from space

(exosphere)