VOLCANOESChapter 11

Section 11-2

VOLCANO

The place where magma reaches the Earth’s surface

VENT

Vent - The opening from which lava erupts

Crater – funnel shaped pit or

depression at the top of a volcano

cone

4 MAJOR TYPES OF LAVA

Type 1 Dark colored Contains lots of

water Rich in iron and

magnesium When this lava

cools, igneous rocks such as basalt are formed

Type 2 Light in color Contains little water Rich in silicon and

aluminum Compounds of these

elements account for the light color

When this lava cools, it forms the igneous rock rhyolite

4 MAJOR TYPES OF LAVA

Type 3 Chemical

composition close to the dark colored type and light colored type

Andesite is an example of the igneous rocks formed

Type 4 Contain large

amounts of gases such as steam and carbon dioxide

Forms rocks with many holes as lava cools because gas bubbles are trapped

Examples are Scoria and Pumice

During volcanic eruptions, many rock fragments are blown in the air.

VOLCANIC DUST:• very fine• Less than .25 millimeter in diameter• Tiny as grains of flour

VOLCANIC ASH:• Particle size is between .25mm to 5

mm• 5 mm is the size of rice grains

VOLCANIC BOMBS:• Centimeter to a meter in size.• Cinders are volcanic bombs the size of

golf balls

Types of Volcanoes

Cinder ConesForm from explosive eruptions of rock particlesLow cone, narrow base, steep sidesParicutin, Mexico

Volcanoes that consist predominantly of pyroclastic materials are called cinder cones. These mountains, such as Capulin Mountain in New Mexico (USA), are easily eroded and usually do not reach great heights.

Types of Volcanoes

Pyroclastic material is another name for a cloud of ash, lava fragments carried through the air, and vapor. Such a flow is usually *very* hot, and moves *rapidly* due to buoyancy provided by the vapors. Pyroclastic flows can extend miles from the volcano, and devastate life and property within their paths. Damage from pyroclastic flows can occur by impact of rock fragments moving at high speeds or burial of the surface with ash and coarser debris a foot or more thick. Hot pyroclastic surges may start fires and kill or burn people and animals. The most devastating pyroclastic flow occured during the eruption of Mt. Pelee in 1902.

Shield VolcanoForms from quiet watery runny lava flow over large areaGently sloping dome shaped mountainsExample: Mauna, Hawaii

Shield volcanoes, on the other hand, are predominantly lava-based landforms that have gradual slopes and wide bases, because they release fluid lava slowly. These volcanoes can create huge landforms. Mauna Loa and Mauna Kea on the island of Hawaii (The Big Island) are classic examples: Mauna Kea has a base on the ocean floor more than 200 kilometres (120 miles) wide.

Shield VolcanoForms from quiet watery runny lava flow over large areaGently sloping dome shaped mountainsExample: Mauna, Hawaii

Composite VolcanoAlternating layers of rock particles and runny lavaViolent eruption first then quiet eruption that covers the rock particlesCone shaped mountainsMt. Fugi

CalderaCrater, top of a volcano, that collapses or explodes to form a large pit

Volcanic Activity• Volcanic activity is unpredictable• In order to indicate reactivity of volcanoes, scientist

classify them as either active, dormant, or extinct.

Active volcano• Erupts continually and periodically• An active volcano is a volcano that has had at least one

eruption during the past 10,000 years.

Dormant Volcano• A sleeping volcano• Known to have erupted in modern times• A dormant volcano is an active volcano that is not

erupting, but supposed to erupt again.

Extinct Volcano• Not known to have erupted in modern times but remain

unpredictable • An extinct volcano has not had an eruption for at least

10,000 years and is not expected to erupt again in a comparable time scale of the future.