Lecture 10: Volcanism and the Chemistry of Magma

Question 1

Volcanology

Answer 1

Study of the origin and ascent of magma through the planet’s mantle and crust and its eruption at the surface

Question 2

Extinct

Answer 2

A volcano that has not erupted during the last several thousand years and is not expected to erupt again; for example, Kilimanjaro, Tanzania

Question 3

Dormant

Answer 3

Volcanoes that have erupted during the last several thousand years but have been quiet in historical times; for example, Mount Meager, British Columbia

Question 4

Active

Answer 4

A volcano is active if it is currently erupting or showing signs of unrest, such as unusual earthquake activity or significant new gas emissions, or if it has erupted in historic time. It’s important to note that the span of recorded history differs from region to region; in the Mediterranean, recorded history reaches back more than 3,000 years but in Hawai`i, little more than 200 years.

Question 5

Stratovolcano

Answer 5

Volcanoes constructed of alternating layers of pyroclastic debris and lava flows; also called composite volcanoes
Med/high viscosity, med/high volatiles, large volume, great slow angle
Andesite

Question 6

Shield volcano

Answer 6

Very wide volcanoes built of low-viscosity lava
Hawaiian
Low viscosity, low volatiles, large volume, low slope angle
Basalt

Question 7

Somma volcano

Answer 7

Volcanic caldera that has been partially filled by a new central cone

Question 8

Caldera

Answer 8

A large (over two kilometres in diameter), basin-shaped volcanic depression, roughly circular in map view, that forms by a piston-like collapse of rock into a partially evacuated magma chamber
Rhyolite

Question 9

Cinder cone

Answer 9

Most common types of volcanic cones
Form after violent eruptions blow lava fragments into the air, which then solidify and fall as cinders around the volcanic vent

Question 10

Viscosity

Answer 10

Resistance to gradual deformation by shear stress or tensile stress – Internal Friction

Question 11

What affects magma viscosity? (3)

Answer 11

1. Gas escape
2. Water content
3. Silica content

Question 12

Most common molecules in magma (3)

Answer 12

O-2, Si+4, SiO2

Question 13

Second most common molecules in magma (2)

Answer 13

Al+3, Al2O3

Question 14

Third most common molecules in magma (4)

Answer 14

Fe+2/+3, CaO, FeO, Fe2O3

Question 15

Affect on magma: Left side of period table

Answer 15

Weaker bonds, therefore weaker magma viscosity

Question 16

Bond energy and breakage

Answer 16

Higher bond energy, harder to break

Question 17

Andesite

Answer 17

52-66% silica

Lava domes and stratovolcanoes

Question 18

Basalt

Answer 18

45-62% silica

Shield volcanoes

Question 19

Dacite

Answer 19

> 63% silica
Caldera
Viscous: explosive

Question 20

Rhyolite

Answer 20

> 66% silica

Caldera

Question 21

Mafic

Answer 21

Basalt
45-52% silicon dioxide
Higher temperature, earlier crystals

Question 22

Intermediate

Answer 22

Andesite

52-66% silicon dioxide

Question 23

Felsic

Answer 23

Rhyolite
>66% silicon dioxide
Lower temperature, latest crystals
Quartz

Question 24

Mid-ocean ridge volcanism

Answer 24

80% of the volcanism on Earth
Eruption on ridges at great depth
Takes time to build up to surface
Important hydrothermal activity

Question 25

Icelandic eruption

Answer 25

``` Gentle eruption, non exposive Low silica content Low viscosity Low gas content Basaltic lava Volcanic plateau and small shield volcanoes ```

Question 26

Hawaiian eruption

Answer 26

``` Gentle eruption, non explosive Low silica content Low viscosity Low gas content Basaltic lava Large shield volcanoes ```

Question 27

Strombolian eruption

Answer 27

``` Gentle eruption, low explosive Low silica content Low viscosity Low gas content Basal to andesitic lava Pyroclastic fragments Scoria cones ```

Question 28

Vulcanian eruption

Answer 28

``` Gentle eruption, moderate explosive Low silica content Low viscosity Low gas content Basalt to andesitic to rhyolite Pyroclastic fragments Scoria cones and stratovolcanoes ```

Question 29

Vesuvian eruption

Answer 29

``` Explosive eruption High silica content High viscosity High gas content Adesitic lava Pyroclastic fragments ```

Question 30

Kratatoan

Answer 30

``` Explosive eruption High silica content High viscosity High gas content Adesitic lava Pyroclastic fragments ```

Question 31

Pelean

Answer 31

``` Explosive eruption High silica content High viscosity High gas content Rhyolitic lava Pyroclastic fragments ```

Question 32

Plinian

Answer 32

``` Explosive eruption, high explosivity High silica content High viscosity High gas content Andesite to rhyolitic lava Pyroclastic fragments Stratovolcanoes ```

Question 33

Volcanic eruptions in order of eruption force (8) | IHSVVKPP

Answer 33

``` Icelandic Hawaiian Strombolian Vulcanian Vesuvian Kratatoan Pelean Plinian ```

Question 34

Direct volcano hazards

Answer 34

``` Lava Pyroclastic flow Nuee Ardentes Pyroclastic surge Ash fall Acid rain Bombs Lahar Debris avalanche Shock wave Lateral blast Gases ```

Question 35

Indirect volcano hazards

Answer 35

Change in groundwater Lack of vegetation Lack of solid ground

Question 36

Yellowstone

Answer 36

``` Resurgent Caldera Eruptions 2.1 Myr ago, 1.3 Myr ago, 0.64 Myr ago (when is the next one?) Lava Creek Tuff 640,000 years ago 1000 km3 of ash ```

Question 37

Can we predict when a volcano will erupt?

Answer 37

``` Eruption recurrence history Infrared photos of cone temp. Temperature of steam Bulges and slope movement Seismic activity ```

Question 38

Long Valley California

Answer 38

``` 760,000 yr ago 400 km3 magma erupted Pyroclastic flows covered > 1500km2 “Bishop Tuff” Long Valley Caldera collapsed 2 km Modern magma chamber: 10 km diameter, 8 km deep 600, 200 years ago Associated with Mount St. Helens, 1980 ```

Question 39

Risk of incorrect prediction?

Answer 39

``` Mammoth Lakes is affluent resort town 20,000 residents during ski season May 1982 USGS issued vol. haz. warning House prices fell 40%, major economic impact ‘Cry wolf’ syndrome ```

Question 40

Mt. Pinatubo

Answer 40

1 Million people Magma rose from 32 km in 500 yrs June 7, 1991 small initial eruption, June 12 millions of m3 erupted, June 15 more than 5 km3 erupted Ash cloud to 35 km in air, 480 km across Blocked sunlight, filled valleys, lahars 300 people died $1.5M monitoring saved 20,000 lives and >$500M evacuated property

Question 41

Canada's volcano hazard

Answer 41

There are more than 200 potentially active volcanoes in Canada, 49 of which have erupted in the past 10,000 years

Question 42

Latest Canadian eruption

Answer 42

Iskut-Unuk River Cones in 1904