Volcanoesare Hot Stuff

Volcanoes I. Volcano: An opening in the earth's crust through which magma flows out as lava• Magma that comes to surface orignates

from the ‘zone of weakness’ in the mantle (zone of weakness is at the base of the plates)

• The plates put pressure on a zone and forces magma up through cracks and openings

Volcanoes

• Most volcanoes are near plate boundaries, where earthquakes occur.

• Exception – Hawaiian islands, in the Pacific Ocean ‘Ring of Fire’– Hot spots form when hot magma from below

earth’s crust rises to the surface

II. Structure• Dormant: volcano quiet or inactive.

Ex: Mt. St. Helen’s was dormant for 100 years

• Extinct: Volcano that has not erupted within historic times. (man was here and recorded) Ex: Mt. Lassen in California until 1913

• Active: Volcano that has erupted & smoke often

II. Structure of Volcanoes

• Crater: is the opening at the top of the volcano

• Lava settles back down into the crus and a solid cap or plug forms in the crater

• Vent is the channel through which the magma travels

II. Structures of Volcanoes• Caldera: A very large crater

located at the top of the volcano

• Laccolith: mass of hardened magma that is dome shaped (magma moves between layers causing bulge)

• Batholith: large mass of igneous rock (hardened magma) below earth’s surface

II. Structures of Volcanoes• Dikes: magma fills

and hardens in vertical cracks

• Sill: a structure of hardened magma between horizontal layers of rock

• Stock: small mass of hardened magma below the earth’s surface

III. Three main types of Volcanoes

• Classified by shape of cone (how lava flows out)

• Cone: Pile of material that collects around the opening

III. Three main types of Volcanoes• 1. Shield Cone: Lava runs out quietly

from the opening and forms gently sloping sides, almost flat, quiet eruptions

• 2. Cinder Cone: An explosive type of eruption and is built up by layers of ash and cinders. (steeper sloped sides than sheild)

• 3. Composite Cone: Both explosive and quiet eruptions. Alternating layers of cinders & lava.flows, (like cake & icing)

Shield Volcano

Cinder Cone Volcanoes

Cinder Cone Volcano

Strato or Composite Volcano

Strato or Composite Volcano

IV. Volcanic Eruptions

• A. Eruptions depend on…..–1. If the vent is blocked or open–2. The length of the vent. (long vents

release gases at high speeds)

B. Four Basic Kind of Eruptions

• 1. Quiet eruption with watery lava flowMagma is thinMagma contains little gasThin lava flows out in a steady stream

• 2. Quiet eruption with thick lava flowMagma contains little gasThick lava forms huge dome

B. Four Basic Kind of Eruptions• 3. Active Eruption

– Thin magma with large amounts of gas– Gas escapes – causes hot magma to shoot out

• 4. Explosive eruption– Magma thick with large amounts of gas– Magma hardens before leaving the vent (blocked)– Trapped gas under high pressure– Sudden release - explosion

V. Types of Materials• A. Lava

–Pahoe hoe – hot, thin, and fast flowing.• Wrinkled surface

–Aa – cooler and thicker• Rough, block – like surface• Jagged, hurts to walk on (‘ah – ah’)

–Pillow lava: forms on ocean floor

V. Types of Materials

• B. Gases– Water vapor – dissolved

water in magma– Carbon monoxide, sulfur

dioxide, & hydrogen sulfide– More gasses trapped and

cannot escape, so pressure builds up and volcano explodes

V. Types of Materials

• C. Pieces of rock (pyroclastic material)– Volcanic dust – smallest, 2 mm or less– Ash – fragments, sand sized– Cinders – sent out by eruptions, several cm

across– Bombs – 1 meter across– Blocks – weighing several tons

Pyroclastic Material: Explosive

Fragments ejected from a volcano:

volcanic bombs

volcanic ashvolcanic blocks

VI. Volcanoes and Man• A. Wiped out civilizations (landscapes)• B. Predicting eruptions

– Mild earthquake activity around the volcano– Plug inside the crater may steam and swell

Problems1. Can cause climate

change (blocking sun with ash)

2. Damage property & people

Benefits1. Ashes spread & creates rich soil2. Hot Springs in Iceland for power3. Colorful sunsets for several years4. Pumice use for polishing

Mt. Vesuvius in Pompeii, Italy

Mt. Vesuvius in Pompeii, Italy