5.5 - Volcanoes and Volcanic Hazards

Volcano

an opening in the earth’s crust from which molten lava, rock fragments, ashes, dust, and gases are ejected from below the earth’s surface.

1. Active Volcano

2. Potentially-active Volcano / Inactive Volcano

3. Dormant/Extinct Volcano

3 types of volcanoes according to activity and historical records

Active volcano

a volcano that has had at least one eruption during the past 10,000 years, might be erupting or dormant.

Potentially active volcano

an active volcano that is not erupting, but supposed to erupt again. Has hazards posed by active volcanoes

Dormant volcano

had not erupted for at least 10,000 years and is not expected to erupt again in a comparable scale of the future

1. Babuyan Claro (Babuyan Island Group, Cagayan)

2. Banahaw (Laguna & Quezon)

3. Biliran/Anas (Leyte)

4. Bud Dajo (Sulu)

5. Bulusan (Sorsogon)

6. Cabalian (Southern Leyte)

7. Cagua (Cagayan)

8. Camiguin de Babuyanes (Babuyan Island Group, Cagayan)

9. Didicas (Babuyan Island Group, Cagayan)

10. Hibok-Hibok (Camiguin)

11. Iraya (Batan Island, Batanes)

12. Iriga (Camarines Sur)

13. Isarog (Camarines Sur)

14. Kanlaon (Negros Occidental & Negros Oriental)

15. Leonard Kniaseff (Davao del Norte)

16. Makaturing (Lanao del Sur)

17. Matutum (Cotabato)

18. Mayon (Albay)

19. Musuan/Calayo (Bukidnon)

20. Parker (South Cotabato, General Santos, North Cotabato, & Saranggani)

21. Pinatubo (Tarlac, Zambales, and Pampanga)

22. Ragang (Lanao del Sur, & Cotabato)

23. Smith (Babuyan Island Group, Cagayan)

24. Taal (Batangas)

24 active volcanoes in the Philippines

1. Mayon

2. Taal

3. Hibok-hibok

4. Pinatubo

5. Kanlaon

6. Bulusan

7. Musuan

7 most active volcanoes in the Philippines

27

Number of potentially active volcanoes in the Philippines

Volcanic eruption

the sudden occurrence of a violent discharge of steam and volcanic material

1. magma composition

2. Temperature

3. volatile/dissolved gases

factors affecting the nature of volcanic eruption (viscosity)

Viscosity

the state of being thick, sticky, and semifluid in consistency, due to internal friction

Temperature

It strongly influence the mobility of lava

silica

the more ________ in magma, the greater its viscosity

water

when dissolved in magma, it tends to increase fluidity because it reduces polymerization, formation of long silicate chains, by breaking silicon-oxygen bonds

• Due to injection of new batch of magma in the system or near the surface.

• Due to pressure and temperature contrast.

• Pressurization due to volatile content

• When sudden geologic activities disturb the chamber such as earthquake, upwelling, etc.

Why do volcanoes erupt?

Eruption Column

Explosive clouds of hot ash and gases that evolve into buoyant plumes produced during eruption of viscous lavas.

• Continued separation of gases from the melt

• Expansion of bubbles as the confining pressure drops

2 processes where bubbles begin to grow

basaltic magma

it produces quiet eruption and continuously flowing lava

acidic magma, andesitic and granitic magma

it results to large and strong eruptions

• Lava

• Volcanic gas

• Pyroclastic materials (blocks, bombs, ash, shards)

Materials extruded during volcanic eruption

Lava flow

stream of molten rock that pour or ooze from an erupting vent

90% basaltic, 10% other composition where 1% is granitic

Composition of lava flow in Earth

• Aa flow

• Pahoehoe flow

Types of lava flow

Aa flow

have surfaces of rough jagged blocks with dangerously sharp edges and spiny projections

Pahoehoe flow

Exhibit smooth surfaces that often resemble the twisted braids of ropes

Pahoehoe

It means “on which one can walk”

False, Pahoehoe lava can be converted to Aa but not vice versa

True or False, Pahoehoe lava can not be converted to Aa and vice versa

Pahoehoe is hotter than Aa

Which type of lava flow is hotter?

Cooling

It increases viscosity and promotes bubble formation in Pahoehoe turning them to Aa

Lava Tube

Hardened basaltic flows commonly contain cave-like tunnels

Lava Tube

They serve as insulated pathways that facilitate the advance of lava great distances from its source

True, it is associated with basaltic lava

True or False, Lava tubes are not associated with volcanoes that emit fluid granitic lava

Block lava

lava that consists of blocks with slightly curved smooth surface rather than the rough clinkery surfaces

Pillow lava

useful in the reconstruction of geologic history whenever they are observed, they indicate that the lava flow formed in an underwater environment

1-6% total weight

Composition of the gaseous portion of most magmas

70% water vapor, 15% CO2, 5% nitrogen, 5% SO2, with lesser amounts of Cl, H, and Ar

Composition of volcanic gases

pyro

it means fire

pyroclast

when volcanoes erupt energetically they eject pulverized rock, lava, and glass fragments from the vent

ash and dust

produced when gas-rich viscous magma erupts explosively

welded tuff

it is formed when the glassy shards in a falling ash fused

>64 mm

size of blocks and bombs

2-64 mm

size of lapilli

<2mm

size of ash

Blocks

they were ejected solid

Bombs

they are semimolten upon ejection, ofthen taking a streamlined shape as they hurtle through the air

Scoria

the name applied to a vesicular ejecta that is a product of basaltic magma

Pumice

the vesicular rock formed from intermediate or felsic magma

• Crater

• Vent

• Conduit (pipe)

• Parasitic cone

Basic parts of volcano

Vent

the surface opening of volcano

crater

located at the summit of most volcanoes, a somewhat funnel-shaped depression

caldera

a crater that has diameters greater than 1 km and in rare cases can exceed 50 km

Parasitic cone

the cone-shaped accumulation of volcanic material not part of the central vent of a volcano

Fumaroles

vents that only releases gas

Shield Volcano

Produced by the accumulation of fluid basaltic lava and exhibit the shape of a broad, slightly dome structure that resembles a warrior’s shield

Canary Islands, Hawaiian Islands, Galapagos, and Easter Island

Examples of Shield volcano

Mt. Mauna Loa

A shield volcano that is considered as the highest feature on Earth

Quiet

Eruption behavior of shield volcanoes

Mt. Kilauea

One of the most active shield volcano on Earth

Cinder Cone / Scoria Cone Volcano

Built from ejected lava fragments that take on the appearance of cinders or clinkers as they begin to harden in flight. They are steep-sided with slopes between 30 and 40 degrees. And they have large, deep craters in relation to the overall size of the structure

Paricutin in Mexico

Example of Cinder Cone

Composite Cone Volcano / Stratovolcano

large, nearly symmetrical structure consisting of alternating layers of explosively erupted cinders and ash interbedded with lava flows

subduction zones

where do stratovolcanoes associated with

Pacific Ring of fire

Stratovolcanoes are usually located in this area

Mt. Mayon, Mt. Fuji

Examples of Stratovolcano

Nuee Ardente

Also called Glowing Avalanche, a pyroclastic flow that consists of hot gases infused with incandescent ash and larger lava fragments

Mt. Vesuvius

A known dormant volcano prior the destruction of Pompeii when it erupted

August 24, 79 AD

When did Mt. Vesuvius erupted

Lahar

Form when magma or pyroclastic materials were erupted and mixed or saturated with water or ice. It may also occur even when a volcano is not erupting.

Crater Lake-type caldera

The collapse of the summit of a large composite volcano following an explosive eruption of silica-rich pumice and ash fragments

Hawaiian-type caldera

The collapse of the top of a shield volcano caused by subterranean drainage from a central magma chamber

Yellowstone-type caldera

The collapse of a large area, cause by the discharge of colossal volumes of silica-rich pumice and ash along ring fractures

Fissure eruption

Rather than building a cone, these long, narrow cracks tend to emit low-viscosity basaltic lavas that blanket a wide area

Flood basalts

The term used to describe the basaltic lavas deposited through fissure eruption

Lava Dome

A dome-shaped mass formed after the lava is squeezed out of the vent

Volcanic Pipes and Necks

Short conduits that connects the magma chamber and vent

Diatreme

rare type of pipe that extends to depths that exceed 200 km

Plate motions provide mechanisms by which mantle rocks melt to generate magma

What is the relationship between plate tectonics and volcanism?

partial melting of mantle rock

it generates magma with basaltic composition

Volcanic Island Arc and Continental Island Arc

The area of volcanism in convergent plate boundaries

Decompression melting

The most common process by which mantle rocks melt where as rock rises, it experiences a decrease in confining pressure and undergoes melting without the addition of heat

Oceanic ridge, Rift valley

Area of volcanism in divergent plate boundaries

Intraplate volcanism

Volcanic activity that occurs within tectonic plates and is generally not related to plate boundaries and plate movements

mantle plume

a mass hotter than normal mantle material that ascends toward the surface

100 to 150 degrees Celsius

the temperature of mantle beneath hot spots

1. Changes in the pattern of volcanic earthquakes

2. Expansion of a near-surface magma chamber, which leads to inflation of the volcano

3. Changes in the amount and/or composition of the gases that are released from a volcano

4. An increase in ground temperature caused by the emplacement of new magma

The 4 most noticeable changes in a volcanic landscape caused by the migration of magma