I. California K-6 Standards for Igneous Activity

II. Goals of This Module

III. Igneous Intrusive Activity

IV. Intrusive Igneous Rock Structures

V. Erupted Materials

VI. Special Features of Extrusive Rocks

VII. Forms of Volcanic Extrusions

VIII. Types of Volcanoes

IX. Types of Volcanic Vents

X. Laboratory Exercises

XI. Possible Essay Questions

XII. Practice Questions

1. Grade 4
1. Earth Sciences Topics
1. Waves, wind, water, and ice shape and reshape the Earth’s land surface. As a basis for understanding this concept, students know:
1. some changes in the Earth are due to slow processes, such as erosion, and some changes are due to rapid processes, such as landslides, volcanic eruptions, and earthquakes.

2. Grade 6
1. Plate Tectonics and Earth’s Structure
1. Plate tectonics explains important features of the Earth’s surface and major geologic events. As the basis for understanding this concept, students know:
1. earthquakes are sudden motions along breaks in the crust called faults, and volcanoes/fissures are locations where magma reaches the surface.

 

2. Shaping the Earth’s Surface
1. Topography is reshaped by weathering of rock and soil and by the transportation and deposition of sediment. As the basis for understanding this concept, students know:
1. earthquakes, volcanic eruptions, landslides, and floods change human and wildlife habitats.

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• To learn how igneous activity, especially volcanic eruptions, shape the surface of the Earth.
• To learn the definitions of and proper spelling for scientific terms that are used commonly in newspapers, magazines, and books, and on television and radio programs to explain igneous events that are occurring in the world.
• To learn the dangers associated with igneous events and the effect that those events have on our environment.

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• Large, underground bodies of melted rock are referred to as magma chambers.
• Cracks in the rock surrounding a magma chamber are invaded (intruded) by the melted rock from the magma chamber.
• Cooling of these masses of melted rock, both in the magma chamber and in the cracks in the surrounding rocks, produces several types of igneous rock structures (plutons).
• Much later in time, these igneous rocks are uplifted by various mountain-building events, and the overlying rocks into which they were intruded are weathered and eroded and stripped away from over the igneous rocks, thus exposing on the surface rocks that originated deep underground.

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Batholith - a cooled magma chamber. Many examples in the San Gabriel and San Bernardino Mountains and the Sierra Nevada of California.

Dike - a sheet-like, cooled intrusion that while hot was injected into a crack that cut across the layering in the surrounding rocks. Several examples occur around Spanish Peaks, New Mexico.

Sill - a sheet-like, cooled intrusion that while hot was injected into a crack that was parallel to the layering in the surrounding rocks. An example is the Palisades Sill along the Hudson River in New York.

Volcanic neck - a pipe-like, cooled intrusion that while hot was injected into a cylindrical vent leading to a volcano. An example is the Devil's Tower in Wyoming.

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• Lava -

Pahoehoe lava is fluid and flows rapidly and smoothly. The temperature is still high and the dissolved gas and water in the lava have not yet completely escaped.

Aa lava is viscous and moves slowly as an expanding pile of hot, broken volcanic rocks. This lava has cooled somewhat and the dissolved gas and water have largely escaped.

• Pyroclastic material -

Material that has been blown explosively out of an eruptive area. This material travels through the air for some distance, then settles to earth as a pile or layer of ashes and cinders. Ashes from very large volcanic explosions will encircle the earth in the upper atmospheric layers and will alter the climate for several years thereafter. Rocks made from pyroclastic material are called tuff.

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Volcanic bombs - Formed from molten lava that has been blown into the air by an explosive eruption and cooled into a spindle shape while in flight.

Lava pillows - Formed from molten lava that has been extruded under water. When lava is extruded under water, the surface of a lava flow cools quickly to form a thin skin around the lava flow. This thin skin cracks easily because of the pressure of the still molten lava inside. Bulbous globs of lava extrude from the cracks, cool quickly, and pile up on one another like a large pile of pillows.

Columnar jointing - Results from the fracturing of magma or lava into many-sided columns as the magma or lava cools and shrinks or contracts in a sill, dike, volcanic neck, or lava flow.

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VII. Forms of volcanic extrusions -

Flood basalts - Extensive, flat-lying basalt flows that erupt quietly from very long fissures (fractures) in the ground. Flood basalts are common in northeastern California and eastern Oregon and Washington.

Volcanoes - Sloping piles of volcanic rock that erupt from and surround a central vent. (Refer to the next section to learn the three types of volcanoes.)

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VIII. Types of volcanoes -

Shield volcano - Made of almost all low-viscosity lava, have gentle slopes, and are the largest volcanoes in the world. Examples are volcanoes in Hawaii and Iceland. Produces the least destructive eruptions. Mauna Loa and Mauna Kea, the two largest volcanoes on the island of Hawaii, are about 30,000 feet tall when you measure from their bases on the bottom of the ocean, 16,000 feet below sea level, to their tops, at about 14,000 feet above sea level.

Cinder cone - Made of mostly pyroclastic material, have steep slopes, and are small. Examples are Parícutin in Mexico and Sunset Crater in Arizona.

Composite volcano (stratovolcano) - Made of alternating layers of viscous lava and pyroclastic material, have intermediate slopes, and are intermediate in size. Examples are Pacific Coast Cascade volcanoes (Mount Saint Helens, Mount Shasta, Mount Lassen), Aleutian Island volcanoes in Alaska, and Andean volcanoes in South America.

Explosive and destructive eruptions that produce pyroclastic flows are typical of this type of volcano. In 1980, Mount Saint Helens in Washington produced a well documented pyroclastic flow that killed several people. In 1902, Mount Pelee on the Caribbean island of Martinique killed 29,000 people (the most killed in a volcanic eruption in the 20th century) when it produced a pyroclastic flow that leveled the town of St. Pierre.

SUMMARY TABLE OF VOLCANO TYPES

VOLCANO TYPE	SIZE	SLOPES	COMPOSITION
SHIELD VOLCANO	LARGE	GENTLE	MOSTLY LAVA FLOWS
COMPOSITE VOLCANO OR STRATOVOLCANO	INTERMEDIATE	INTERMEDIATE	BOTH LAVA FLOWS AND PYROCLASTIC MATERIAL
CINDER CONE	SMALL	STEEP	MOSTLY PYROCLASTIC MATERIAL

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IX. Types of volcanic vents -

Crater - a funnel-shaped depression at the top of a volcano formed as a result of explosive eruptions. Most composite volcanoes have one or more craters.

Caldera - a very large depression at the top of a volcano formed most commonly by collapse of the roof of the magma chamber after cooling and shrinking of the magma. Most shield volcanoes have calderas, such as Mauna Loa and Kilauea in Hawaii. Crater Lake in Oregon is a water-filled caldera in an ancient composite volcano.

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X. Laboratory exercises -

• MAKE A VOLCANO MODEL -
• WRITE ABOUT VOLCANO DESTRUCTION -

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XI. Possible essay questions -

• Illustrate, define, and describe the origin of four types of igneous intrusive features.
• Describe the origin of three extrusive igneous features.
• Compare and contrast the two major types of lava flows.
• Name three types of volcanoes, describe their origins, and illustrate them with rather precise illustrations.
• Name two types of volcanic vents, describe their origins, and illustrate them with rather precise illustrations.

 

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XII. Practice questions -

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