Geo exam 3

Sketch and describe the four main types of volcanoes that construct hills and mountains.

Scoria Cone- several hundred meters high, small crater at summit. Has Loose or Black pebbles Shield Volcano- broad, gently sloped curves. Contain basaltic lava flows with little ash Composite Volcano- Symmetrical, thousands of meter high, steep slopes and crater. Smaller than shield volcanos, and has pyroclastic deposits Volcanic Dome- Hundreds of meters high. contain a solidified lava, contain volcanic ash and felsic magma erupts

Sketch or summarize how you would recognize a shield volcano in the landscape.

has a conduit which is a pipeline of magma and contains fissure which is vertical, sheet like magma chambers

Describe the characteristics of flood basalts and how they erupt.

Are sequences of basaltic lava flows that cover vast areas and commonly have thickness of several kilometers. They erupt from a single, central volcantic vent, flood basalt erupt from one or more long, nearly continuous fissures or from a linear string of vents.

Describe the processes on composite volcanoes and the rocks they form.

Are so named because they are a composite of interlayered lava flows, pyroclastic flow, tephra falls, and volcano-related mudflows and other debris. Rocks the volcano consists of alternating layers of pyroclastic flows, lava flows, and landslides and mudflow deposits.

List the kinds of rocks you might find in a caldera from top to bottom.

At the top you would find ash rich sediments trapped in caldera, then rocks with or without crystals and in the deep is crystalline granite in the magma chamber.

Describe the tectonic setting of most composite volcanoes.

Consist mostly of intermediate lava and ash, but they can also include felsic and mafic materials. The combination of diverse magma composition and different styles produce a variety of rock types and volcanic features .

Describe the difference between an eruption column and pyroclastic flow, and the role that gas plays in eruptive style.

Eruption column form when magma is ripped apart by volcanic gases erupts high into the atmosphere. Pyroclastic flow some ash does not form not jet straight up but collapses down the side of the volcano a dense, hot cloud of ash pyroclastic flow or simply as an ash flow.

Sketch and explain the stages in the formation of a caldera.

First stage- crustal melting of felsic magma, has many chambers Second Stage- Magma reaches the surface and eruptions begin. Roof of the chamber begins to collapse Third Stage- The magma forms eruption columns and pyroclastic flow, thick ash Fourth Stage- eruption is over and a deep depression is formed

What are two ways a volcanic dome can grow?

From the inside or outside. -From the inside- as magma injects into interior of the dome, new material causes it to expand upward and outward, fracturing the partially solid outer crust, creating blocks of rubbly solid lava that covers outside of dome. From outside- domes can grow as magma breaks through to surface and flows outward as thick, slow, lava. As magma moves further, the front cools and solidifies, and can collapse into angular blocks

Explain how risk is different than hazard, and provide an example of each.

Hazard is the existence of Potentially dangerous situation or event, such as a landslide. Risk is an assessment of whether the hazard might have some societal impact, such a loss of life, damage of property and etc.

What's the characteristics of a Caldera

Large basin-shaped volcanic depression that can be filled with volcanic materials

Describe four ways that magma erupts

Lava flow, lava fountain, dome, eruption column

Describe how viscosity influences how explosive an eruption is.

More viscous:difficult to flow, and traps gas

Identify some examples of composite volcanoes from around the world.

Mt. Fuji, Mt. Kilimanjaro, Mt. Etna.

Sketch and describe how basaltic magma may form a scoria cone, lava flow, or both.

Scoria cones are loose piles of material that erode rapidly. Basalt flows are considerably more resistant to weathering and erosion and are more likely to survive in the geologic record. Scoria cones and lava flow typically occur in clusters called volcanic fields.

Describe the difference between hazards associated with scoria cones and hazards associated with basaltic flows.

Scoria cones can be deadly and destructive, especially to nearby areas, as they hurl lava and solid and spew out dangerous gases. Basaltic flows are a special type of hazard is associated with erupting volcanoes beneath ice sheets. The heat from such eruptions can melt large quantities of ice and produce huge floods.

Explain the characteristics of scoria cones and basalt flows, including the associated rock types and features.

Scoria cones, pieces of scoria from the lava fountain gradually builds up a cone shaped hill. Basaltic eruptions, at the beginning of a basaltic eruption, gases explode bits of lava into the air.

Explain how shield volcanoes erupt.

Shield volcano erupt mostly low-viscosity basaltic lava and so are dominated by relatively nonexclusive outpouring of lava from fissures and vents.

•Describe the type of magma and other general characteristics of a shield volcano.

Shield volcano have a board, shield-shaped form and fairly gentle slopes when compared to other volcanoes. They are constructed by a succession of basaltic lava flows and lesser amounts of scoria and ash. Shield volcano can form in any tectonic setting that produces basaltic magma.

Describe the types of rocks associated with volcanic domes.

Some parts of domes cool rapidly into volcanic glass, such as obsidian and flow bands, formed by shearing and other processes during flow. Rhyolite consisting of very small crystals. Volcanic breccia are consolidated or incorporated into magma. Tuff and are other debris that are in the domes.

Describe how the plate tectonic setting of a region influences its potential for volcanic hazards

Tectonic setting, especially proximity to certain types of plate boundaries, is a major factor controlling regional, variation of volcanic hazards.

Explain how gas behaves at different depths in a magma and how it influences eruptive style.

The dissolved gas was always there in the liquid but only became visiable bubbles when you open the top and releases the pressure that held the gas in solution. Water helps the magma rise toward the surface. Pressure keeps most of the gases in solution and keeps bubbles from forming. As the magma approaches the surface, confining pressure diminishes and the gases remain in solution.

Describe how you might recognize a volcanic dome in the landscape.

They are partially eroded shape and unaltered volcanic glass, when they collapse the release of pressure causes pyroclastic flows and avalanches of rock and other debris.

Describe the characteristics of a volcanic dome.

They have a nearly perfect domal shape, but most have a more irregular shape because some parts of the dome have grown more than other parts or because one side of the dome have collapsed downside.

Describe or sketch the characteristics of a composite volcano, including its internal structure.

mt st helens. has interlayered lava flows, pyroclastic flows, tephra falls and mudflows. Erupt over long periods of time