Geology Chapter 5 Concepts

5.3 List the main gases released during a volcanic eruption. What role do gases play in eruptions?

- water vapor, carbon dioxide, nitrogen, and sulfur dioxide - important because they contribute significantly to our planet's atmosphere

5.9 What type of volcanic structure is Shiprock, New Mexico, and how did it form?

-It's a volcanic neck or plug They form when lava in a conduit becomes cool. When the volcano then erodes because it weathers, the neck forms

5.9 Pyroclastic flows are associated with what volcanic structure that is not a cinder cone?

Associated with calderas

*5.7 Explain the formation, distribution, and characteristics of composite volcanoes.

Composite volcanoes are called " composite" because they consist of both pyroclastic material and lava flows. They typically erupt silica- rich lavas that cool to produce andesite or rhyolite. They are much larger than cinder cones and form from multiple eruptions over a million years or longer.

5.2 The eruption of what type of magma may produce an eruption column?

Highly viscous (slow), silica-rich magmas

5.2 Why is a volcano that is fed by highly viscous magma likely to be a greater threat to life and property than a volcano supplied with very fluid magma?

Highly viscous magma may produce explosive clouds of hot ash and gases that evolve into buoyant plumes called eruption columns, because of the high viscosity of the silica-rich magma, a significant portion of the volatiles remain dissolved until the magma reaches a shallow depth, where tiny bubbles begin to form and grow. The bubbles and pressure create explosive reactions. But, when fluid lava erupts, the pressurized gases escape with relative ease.

5.5 Where are the best-known shield volcanoes in the United States? Name some examples in other parts of the world.

In Hawaii. Canary Islands, Galapagos, and Easter Islands

5.5 Where do most shield volcanoes form - on the ocean floor or on the continents?

In the ocean.

5.2 List these magmas in order from most silica rich to least silica rich, based on their compositions: mafic (basaltic), felsic (rhyolitic), intermediate (andesitic).

Rhyolitic - highest silica content at 70% Andestic - silica content is 60% Mafic - magma has least silica content with about 50%

5.3 What is scoria? How is scoria different from pumice?

Scoria is the name applied to vesicular ejecta that is a product of basaltic magma and black to redish brown. When magmas with intermediate or felsic compositions erupt explosively, they emit ash and vesicular rock called pumice. Pumice is lighter in color and less dense than scoria and many have so many vesicles they are light enough to float.

5.7 How do the composition and viscosity of lava flows differ between composite volcanoes and shield volcanoes?

Shield volcano - made of basalt and is fluid (fluid - fast flow) Composite - magma is high in silicon; makes it viscous (slow flow)

*5.5 Summarize the characteristics of shield volcanoes and provide one example.

Shield volcanoes consist of many successive layers of low- viscosity basaltic lava and lack significant amounts of pyroclastic debris. Lava tubes help transport lava far from the main vent, resulting in very gentle, shield- like profiles.

5.6 How do the size and steepness of slopes of a cinder cone compare with those of a shield volcano?

Simple shape. Has a steep side. Broad and domed.

5.3 How do lava tubes form?

in the interior of a flow where temperatures remain high long and cools and hardens

5.3 How do volcanic bombs differ from blocks of pyroclastic debris?

pyroclastic debris is made of hardened lava, and volcanic bombs are made of incandescent lava.

5.10 Volcanism at divergent plate boundaries is most often associated with which rock type? What causes rocks to melt in these settings?

Basaltic Rocks Sea floor spreading Lithosphere plates keep going up under axes. Then, mantle gets solid and reacts to decrease in burden by going up to fill the rift. Rock rises, confines pressure, and leads to melting. This process is called decompression.

*5.1 Compare and contrast the 1980 eruption of Mount St. Helens with the eruption of Kilauea, which began in 1983 and continues today.

Both emit lava. But a typical eruption of Hawaii's Kilauea volcano is gentle, much less violent than the largest volcanic eruption to occur in North America by Mount St. Helens

5.1 Briefly compare the May 18, 1980, eruption of Mount St. Helens to a typical eruption of Hawaii's Kilauea Volcano

Both emit lava. But a typical eruption of Hawaii's Kilauea volcano is gentle, much less violent than the largest volcanic eruption to occur in North America by Mount St. Helens

*5.9 List and describe volcanic landforms other than volcanic cones.

Calderas are among the largest volcanic structures. They form when the stiff, cold rock above a magma chamber cannot be supported and collapses to create a broad, bowl- like depression. Fissure eruptions produce massive floods of low- viscosity, silica- poor lava from large cracks in the crust.

*5.6 Describe the formation, size, and composition of cinder cones.

Cinder cones - steep, made of pyroclastic debris, small relative to other volcanoes, mostly basaltic composition. They form quickly in single eruptions

5.4 Distinguish among conduit, vent, and crater.

Conduit - path of lava from vent to edge of volcano Vent - circular opening of a conduit Crater - funnel-shaped crater and depression that is at the top of the volcano

5.4 How is a crater different from a caldera?

Crater - form when a large magma chamber is emptied by a volcanic eruption or by subsurface magma movement Caldera - unsupported rock that forms the root of the magma chamber then collapses to form this

5.9 Describe the formation of Carter Lake. Compare it to the calderas found on a shield volcanoes such as Kilauea.

Crater Lake caldera is about six miles in diameter and formed following a major eruption of ash and pyroclastic flows about 7000 years ago. Kilauea is about three miles in diameter and acts somewhat like a floating cork, rising when magma is accumulating and sinking after an eruption. The rising and sinking movements are gradual.

5.10 At which of the three types of plate boundaries is the greatest quantity of magma generated?

Divergent plate boundaries

*5.2 Explain why some volcanic eruptions are explosive and others are quiescent

Explosive - big Quiescent - gentle and small Viscosity Magmas with higher viscosities result in more explosive eruptions and magmas with lower viscosities result in less explosive, more quiescent eruptions. Higher viscosities prevent dissolved gases from escaping, so the gases build up more and more pressure as the magma cools as the gases bubble out of the solution, trying to escape. Eventually, the gas pressure results in an explosive eruption, whereas in lower viscosity magmas, the gases more easily escape and therefore much less pressure builds up and the resulting eruption is more fluid.

*5.3 List and describe the three categories of materials extruded during volcanic eruptions.

Lava - magma Gases - a bunch of dissolved gases most in the form of water vapor Pyroclastic materials - ash and dust particles and other particles involved in the eruption of the volcano

5.9 Contrast the composition of a typical lava dome and a typical fissure eruption.

Lava dome - emits lava with silica rich pumice, ash, and debris Fissure eruption - emits fluid basaltic lava

5.5 Relate lava tubes to the extent of lava flows associated with shield volcanoes.

Lava tubes are things that lava flows through. In shield volcanoes, most of the flow of the lava occurs in the lava tubes.

*5.4 Label a diagram that illustrates the basic features of a typical volcanic cone.

Look at page 135

5.6 Describe the composition of cinder cones.

Made of scoria lava fragments form together and harden to make the scoria Composed of basaltic material

5.7 Describe the materials that compose composite volcanoes.

Made-up of magma that is silicon rich. Magma is andesitic. Also can have pyroclastic with felsic silica composition

5.2 Explain how the viscosity of magma influences the explosiveness of a volcano.

Magma gets high dissolved gas content - it becomes less viscous. Due to the gas, the volcano gets more explosive. Less viscous (slow), more explosive

5.10 What is the source of magma for most intraplate volcanism?

Mantle plume

5.8 What is a lahar?

Mudflow that goes down the slopes of a volcano. Very destructive

5.7 What zone on Earth has the greatest concentration of composite volcanoes?

Pacific ocean - Ring of Fire

5.3 Describe pahoehoe and aa lava flows.

Pahoehoe Flows - exhibit smooth surfaces that often resemble the twisted braids of ropes Aa Flows - have surfaces of rough jagged blocks with dangerously sharp edges and spiny projections

5.4 What is a parasitic cone, and where does it form?

Parasitic cones form from fissures in the side or base of the volcano. Eruption from these fissures may produce cones called parasitic cones.

5.10 How is magma along generated convergent plate boundaries?

Partial melting associated with a subducting slab seems to begin at depths of about 100 km. Fluids released from the slab promote melting of hot peridotite in the overlying lithosphere. Also, materials at the top of the slab, such as sediments, hydrated volcanic rocks, and continental-rock slivers are in contact with hot, non-slab peridotite and may undergo partial melting. As the slab tip penetrates to deeper levels, upward, counter flows of hot peridotite are set in motion, resulting in decompression melting and production of basaltic magma. Look at page

5.5 Describe the composition and viscosity of the lava associated with shield volcanoes.

Produced by the accumulation of fluid basaltic lavas. -High viscosity

*5.8 Discuss the major geological hazards associated with volcanoes.

Pyroclastic flow - when ash and stuff goes out around the volcano Lahar - mudflows on cones (inactive and active) Tsunamis, ash that hits planes, gases that people breath

5.9 How do the eruptions that created the Columbia Plateau differ from eruptions that create large composite volcanoes?

Rather than build cones, fissure eruptions usually emit fluid basaltic lavas that blanket wide areas

5.5 Are pyroclastic materials a significant component of shield volcanoes?

They are not. Basalt is higher than the pyroclastic material.

5.8 Describe pyroclastic flows and explain why they are capable of traveling great distances.

They have hot gas and burning lava with ash. They are helped to move quickly by gravity. Expanding ash removes friction so it moves faster

5.8 List at least three volcanic hazards other than pyroclastic flows and lahars.

Tsunami Vocanic ash Volcanic gases

5.4 What is a fumarole emit?

Vents that only emit gases

5.10 Are volcanoes in the Ring of Fire generally described as quiescent or explosive? Name an example that supports your answers.

Violent so they are explosive Mount Kilimanjaro

5.2 Define viscosity and list three factors that influence the viscosity of magma.

Viscosity is how quickly magma can move and flow. If it is more viscous, it is more resistant to flowing (slower) Temperature - magma cools becomes more viscous, composition - high silica content is more viscous, and dissolved gases - more dissolved gasses, it is less viscous

*5.10 Relate the distribution of volcanic activity to plate tectonics.

Volcanoes occur at both convergent and divergent plate boundaries, as well as in intraplate settings. The greatest volume of magma is produced at divergent plate boundaries (60 percent of Earth's total yearly output)

5.6 Over what time span does a typical cinder cone form?

Within a year