Geology Test 2 Review

Briefly describe three ways that soil erosion is controlled.

Terrace farming - keeps steep slopes flat Planting crops - slow the run of water Grassed waterway - protects crops from formation of gullies

List the two criteria by which igneous rocks are classified

Texture and mineral composition

What role do water and other volatiles play in the formation of magma?

They act as salt does to ice. Water causes rock to melt at lower temperatures, just as putting rock salt on an icy sidewalk induces melting.

How do joints promote weathering?

They're fractures that allow water to penetrate deeply and start the process of weathering long before the rock is exposed

How does the rate of cooling influence crystal size? What other factors influence igneous rocks?

Three factors influence the textures of igneous rocks: 1. the rate at which molten rock cools 2. the amount of silica present in the magma 3. the amount of dissolved gases in the magma Slow cooling permits ions to migrate freely until they eventually join one of the existing crystals. Promotes the growth of fewer, but larger crystals.

What is the overriding goal of volcano monitoring?

To discover precursors that may warn of an impending or imminent eruption

In what way does tuff and volcanic breccia differ from other igneous rocks such as granite and basalt

Tuff and volcanic breccia do not imply mineral composition. - they are frequently identified with a modifier - for example, rhyolite tuff indicates a rock composed of ash size particles having a felsic composition

Are volcanoes in the ring of fire generally described as quiescent or violent? Name an example

Violent Eruption at Mt. St Helends

Assimilation

changes the overall chemical composition of the magma body

What minerals are most abundant in detrital sedimentary rocks? In which rocks do these minerals predominate?

clay minerals and quartz

Describe the composition of a cinder cone

composed mostly of loose scoria fragments, some produce extensive lava fields.

Explain how human activities have affected the rate of soil erosion.

human activities such as farming, logging, and construction, which remove or disrupt the natural vegetation, have greatly accelerated the rate of soil erosion

How do lava tubes form?

in the interior of a flow where temperatures remain high long after the surface hardens

What is the source of magma for intraplate volcanism?

mantle plumes

Magma mixing

occurs during the ascent of two chemically distinct magma bodies as the more buoyant mass overtakes the more slowly rising body. once they are joined, convective flow stirs the two magmas, generating a single mass that has an intermediate composition.

Volcanism at divergent plate boundaries is associated with which rock type? What causes rocks to melt in these regions?

- The greatest volume of magma is produced along the oceanic ridge system in association with seafloor spreading - As rock rises, it experiences a decrease in confining pressure and undergoes melting without the addition of heat.

List two ways in which sedimentary rocks are important.

-Contain sources of energy like coal, oil, and natural gas -Contain fossils used to study the past

List the 6 major igneous rock textures

1. Aphanitic (fine-grained) - composed of crystals that are too small for the individual minerals to be identified without a microscope 2. Phaneritic (coarse-grained) -Composed of mineral grains that are large enough to be identified without a microscope 3. Porphyritic - Composed of two distinctly different crystal sizes 4. Vesicular -Extrusive rock containing voids left by gas bubbles that escape as lava solidifies 5. Glassy - composed of unordered atoms and resembles dark manufactured glass 6. Pyroclastic (fragmented) - Produced by consolidation of fragments that may include ash, once molten blobs, or large angular blocks that were ejected during an explosive eruption

What 3 factors do volcanologists monitor in order to determine whether magma is migrating toward earth's surface?

1. Changes in the pattern of earthquakes produced by the movement of magma 2. Magma entering a near-surface magma chamber, which leads to inflation of the volcano 3. Changes in the amount or composition of gases released from a volcano

Places these phenomena related to soil in the proper sequence: sheet erosion, gullies, raindrop impact, rills, stream.

1. Raindrop Impact 2. Stream 3. Sheet Erosion 4. Rills 5. Gullies

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

70% water vapor, 15% CO2, 5% Nitrogen, and 5% SO2.Lesser amount of chlorine, hydrogen and argon as well.

Over what time span does a typical cinder cone form?

95% formed in less than a year

How is a crater different from a caldera?

A crater is a funnel shaped pit at the top of a volcanic vent whereas a caldera is a basin shaped depression formed when the volcanic cone collapses due to magma chamber below getting empty of magma.

What is lahar?

A debris flow on the slopes of a volcano that results when unstable layers of ash and debris become saturated and flow downslope, usually following stream channels

Name two plate tectonic settings in which you would expect magma to be generated.

A decrease in pressure, or the heating of crustal rocks above there melting temperature

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

A highly heated mixture, largely of ash and pumice fragments, that travels down the flanks of a volcano or along the surface of the ground. Propelled by Gravity

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

A parasitic cone is the cone-shaped accumulation of volcanic material not part of the central vent of a volcano. It forms from eruptions from fractures on the flank of the volcano.

List at least three volcanic hazards besides pyroclastic flows and lahars.

Acid rain, ash fall, tsunamis

What is meant by the term country rock?

Also known as "host rock", this is when magma rises through the crust, it forcefully displaces preexisting crustal rocks.

Describe how an exfoliation dome forms.

As the overburden is removed, the outer parts of the granitic mass expand more than the rock below and separate from the rock body. Continued weathering eventually causes the slabs to separate and peel off, creating an exfoliation dome.

Why are soils classified?

Bringing order to large quantities of information not only aids comprehension and understanding but also facilitates analysis and explanation

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

Built primarily of fluid basaltic lava flows and contains only a small percentage of pyroclastic material. In its early stages it viscosity is very low.

How do cinder cones compare to shield volcanoes in terms of size and steepness of their flanks?

CC: Slopes of 30- 40 degrees on its flanks Shield: This type of volcano has steeper slopes of 6-10 degrees on its flanks

How is carbonic acid formed in nature?

Carbonic acid forms when water absorbs the carbon dioxide in the air when it falls as rain.

Igneous rocks are composed mainly of which group of minerals?

Composed mainly of silicate materials. -silicon and oxygen are by far the most abundant constituents of igneous rocks -Plus ions of Al, Ca, Na, K, Mg, Fe -These make up about 98% of most magmas

Describe the process of crystallization

Cooling reverses the events of melting. as the temperature of the liquid drops, ions pack more closely together as their rate of movement slow. When they are cooled sufficiently, the orcas won the chemical bonds will again confine the ions to an orderly crystalline arrangement.

Distinguish among a conduit, a vent and a crater.

Craters are located at the summit of most volcanic cones and is a somewhat funnel-shaped depression. Conduit- a natural channel through which something is conveyed (circular) Vent is an opening exposed on the earths surface where volcanic material is emitted.

List and briefly describe the differences among the three basic sedimentary rock categories.

Detrital: accumulation of material that originates and transported as solid particles Chemical: soluble material produced largely by chemical weathering Organic: bits and pieces of undecayed plant material

Describe Dikes and Sills

Dikes: discordant bodies that form wheeb magma is forcibly injected into fractures and cut across bedding surfaces and other structures. Dikes serve as tabular conduits that transfer magma. Sills: Nearly horizontal concordant bodies that form when magma exploits weaknesses between sedimentary beds or other rock structures.

Describe each of the following in terms of composition and texture:

Diorite: - coarse grained, looks like gray granite - salt and pepper color - no visible quartz, high dark silicates - primarily plagioclase feldspar and amphibole Rhyolite: - fine-grained, light colored silicates - buff pink to light gray -contains glass fragments Basalt porphyry: - very dark green to black - fine grained - glassy appearing olivine grains

Which type of plate boundary is the greatest quantity of magma generated?

Divergent

Why are soils in tropical rain forests not well suited for farming?

Each year, millions of acres are cleared for agriculture and lodging. This results in soil degradation, loss of biodiversity, and climate change. Rain forest clearing not only removes plant nutrients, but also accelerates soil erosion.

identify three particularly extensive soil orders that occur in the contiguous 48 United States.

Entisol has 16.16%, Aridisol 12.02%, Alfisols 9.65%

How are most basaltic magmas thought to be formed?

Experiments show that under the high pressure conditions calculated for the upper mantle, partial melting go the ultramafic rock peridotite can generate a magma of basaltic composition

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

Formed 7000 y/a when a composite cone (Mt. Mazama) violently extruded 50 to 70 cubic kilometers of pyroclastic material Unlike Crate lake type calderas, many calderas form gradually because of the loss of lava from a shallow magma chamber underlying the volcano's summit

Explain how water can cause mechanical weathering.

Frost wedging, after water works its way into the cracks in rock, the freezing water enlarges the cracks, and angular fragments eventually break off.

What is emitted from a fumarole?

Gases and steam

How are Granite and Rhyolite...similar...or different?

Granite - coarse-grained rock, 10-20% quartz, roughly 50% feldspar -rounded, glassy, clear to gray Rhyolite -fine-grained -like granite, is composed of light colored silicates -used less often than granite

Explain why the headstones in Figure 6.13 have weathered so differently.

Granite is a silicate mineral, which is more resistant to chemical weathering. Marble is composed of calcite, which dissolves in weakly acidic solution, such as rainwater.

List the four basic compositional groups of igneous rocks, in order from the group with the highest silica content to the group with the lowest silica content.

Granitic (felsic)- highest silica content Andesitic (intermediate)- 2nd highest silica content Baslatic (mafic)- 3rd lowest in silica content Ultramafic- lowest in silica content

Name two minerals typically found in rocks with high silica content and two minerals found in rocks with relatively low silica content.

Granitic magma has high silica content, as does andesite Basaltic magma are low in silica content, as it peridotite

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

Hawaii, Galapagos Islands, Canary Islands

What type of magma must erupt to produce an eruption column?

Highly viscous magmas must erupt to produce an eruption column.

Define Bowen's reaction series.

If solid components in a magma reamin in contact with the remaining melt, they will chemicals react and change mineralogy.

How might the direction a slope is facing influence soil formation?

In the midlatitudes of the Northern Hemisphere, a south-facing slope receives a great deal more sunlight than a north-facing slope. The difference in the amount of soil radiation received causes differences in soil temperature and moisture, which in turn influence the nature of the vegetation and the character of the soil.

Describe the following features of processes: eluviation, leaching, zone of accumulation, and hardpan.

Leaching: the depletion of soluble materials from the upper soil Eluviation: The washing out of fine soil components Zone of accumulation: the area above the firn line, where material accumulates Hardpan: a dense layer of soil, usually found below the uppermost topsoil layer.

Compare and contrast intrusive and extrusive igneous rocks.

Intrusive igneous rocks: when magma crystallizes at depth. - also known as "plutonic rocks" observed at the surface where uplifting and erosion have stripped away the underlying rocks. Extrusive igneous rocks: when molten rock solidifies at the surface - also known as "volcanic rocks" form when lava solidifies or when volcanic debris falls to Earth's surface

What products result when carbonic acid reacts with potassium feldspar?

It breaks down into the clay mineral kaolinite.

What occurs when carbonic acid reacts with calcite-rich rocks such as limestone?

It is easily attacked by weakly acidic solution.

What does a porphyritic texture indicate about the cooling history of an igneous rock?

It required thousands or even millions of years to solidify, meaning the cooling process was slow.

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

Just as shield volcanos owe their shape to fluid basaltic lavas, composite cones reflect their viscous nature from which they are made

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

LD: A bulbous mass associated with an old-age volcano, produced when thick lava is slowly squeezed from the vent. Lava domes may act as plugs to deflect subsequent gaseous eruptions FE: An eruption in which lava is extruded from narrow fractures or cracks in the crust

Distinguish among batholiths, stocks, and laccoliths in terms of size and shape.

Laccoliths: igneous rocks forcibly injected between sedimentary strata, so as to arch the beds above while leaving those below relatively flat. Batholiths: "deep stone", by far the largest intrusive igneous body, occasionally as mammoth linear structures several hundred kilometers wise. Produced by hundreds of discrete injection of magma that form smaller intrusive bodies that intimately crowd against or penetrate each other Stocks: Smaller than batholiths, but would be classified as batholiths if they were fully exposed.

In addition to composite volcanoes, what other volcanic landform can generate a pyroclastic flow?

Lava dome

List and describe the 3 components of magma

Liquid component: "melt" composed mainly of mobile ions of the 8 more common elements of Earth's crust- silicon, oxygen, aluminum, P Ca, Na, Iron, Magnesium. Solid component: in magma are crystals of silicate materials Gaseous Component: "volatiles" are materials that vaporize (form gas) at surface pressures. - the most common volatile found in mage are water vapor, CO2 and SO2.

What is magma? How does magma differ from lava?

Magma is completely or partly molten rock which when cools, solidifies to form igneous rocks composed mainly of silicate materials. Lava is when molten rock reaches the surface.

What are the two basic categories of weathering?

Mechanical and chemical breakdown of rock at or near Earth's surface

How do the products of each category of weathering differ?

Mechanical weathering is accomplished by physical forces that break rock into smaller and smaller pieces without changing the rocks mineral composition. Chemical weathering involves a chemical transformation of rock into one or more new compounds.

Are volcanoes fed by highly viscous magma more likely or less likely to be a greater threat to life?

More. Highly viscous magma is the most destructive to property and human life.

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

Most form on the ocean floor, although it is less common for them to form on the continental crust.

What is the process that is thought to generate most granitic magmas?

Most granitic magmas probably form when hot basaltic magma ponds below the continental crust. When the heat from the hot basaltic magma partially melts the overlying crustal rocks, which are silica rich and have a much lower melting temp, the result can be the production of large quantities of granitic magma.

Are pyroclastic materials a significant component of shield volcanoes?

No

Contrast pahoehoe and aa lava flows.

Pahoehoe flows exhibit smooth surfaces, are hotter, and are more fluid than aa flows, which exhibit jagged surfaces with sharp edges.

List the five basic controls of soil formation. Which factor is most influential in soil formation?

Parent material, climate, plants and animals, time, topography. Climate is considered to be the most influential control of soil formation.

What is the primary basis for distinguishing among various detrital sedimentary rocks?

Particle size

How does biological activity contribute to weathering?

Plant roots in search of nutrients and water grow into fractures, and as the roots grow, they wedge apart the rock. Burrowing animals further break down rock by moving fresh material to the surface where physical and chemical processes can more effectively attack it. Decaying organisms also produce acids that contribute to chemical weathering.

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

How is regolith different from soil?

Regolith does not contain organic matter, water, and air.

List the three magmas in order from the most silica rich to the least silica rich, based on their composition: basaltic magma, rhyolitic magma, and andesitic magma.

Rhyolitic- 70% silica content Andesitic- 60% silica content Basaltic- 50% silica content

Using a soil texture triangle, what type of soil would have a composition of 60% sand, 30% silt, and 10% clay?

Sandy loam has 60% of sand Clay has 30% slit Sand has 10% clay

What is scoria? How is scoria different from pumice?

Scoria is the name applied to vesicular ejecta produced from basaltic magma. Pumice is usually lighter in color and less dense than scoria, and many pumice fragments have so many vesicles that they are light enough to float.

How does the volume of sedimentary rocks in Earth's crust compare to the volume of igneous and metamorphic rocks?

Sedimentary rocks represent 5 to 10 percent of the crust, whereas igneous rocks and metamorphic rocks combined represent 90 to 95 percent of Earth's crust.

What are two detrimental effects of soil erosion, aside from the loss of topsoil

Sedimentation Chemical pollution

Outline the steps that would transform an exposure of granite in the mountains into various sedimentary rocks.

Sediments and soluble constituents are typically transported downslope by gravity The sediments are then deposited and subsequently buried As deposition continues, the sediments are lithified into sedimentary rocks

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

Shiprock is a volcanic neck: an isolated, erosional remnant consisting of lava that once occupied the vent of a volcano As erosion progresses, the rock may remain standing above the surrounding terrain long after the cone has been worn away

Why is soil considered an interface in the Earth system?

Soil forms where the geosphere, atmosphere, hydrosphere, and biosphere meet.

Describe the materials that compose composite volcanoes.

Stratovolcanoes are called composite volcanoes because they made from a series of eruptions that have occurred over thousands of years. The eruptions that form these volcanoes lay down alternating layers of lava, ash, cinders and pyroclastic material

List several minerals that are especially susceptible to oxidation and list two common products of oxidation.

Susceptible minerals include olivine, pyroxene, hornblende, and biotite. Common products of exfoliation are hematite and limonite.

How does climate affect weathering?

Temperature and moisture are the main factors in weathering- warm temperatures with high moisture are best for weathering. Frigid areas are bad for weathering, as moisture is locked.

Why is texture an important soil property?

The texture of soil strongly influences the soil's ability to transmit water and air.

What is the name given to the region having the greatest concentration of composite volcanoes.

The Ring of Fire

Explain how the crystals in pegmatites are able to grow so large

The crystals in pegmatites are abnormally large because ion migration is enhances in these fluid-rich environments, where they form late in the crystallization of magma when water and other materials make up a high percentage of melt.

How do light-colored igneous rocks differ from dark-colored igneous rocks?

The dark (ferromagnesian) silicates are rich in iron and/or magnesium and comparatively low in silica. - Olivine, pyroxene and amphibole, and biotite mica are the common dark silicate minerals of Earth's crust The light (nonferromagnesian) silicates contain greater amount of K, Na, Ca, rather than Fe and Mg -the light silicates include quartz, muscovite mica, and feldspars and richer in silica than the dark silicates.

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

Viscosity means the magmas mobility. The more viscous the material, the greater its resistance to flow. Temperature, composition, and amount of dissolved gas influence the viscosity of magma.

When a rock is mechanically weathered, how does its surface area change? How does this influence chemical weathering?

When a rock undergoes mechanical weathering, it is broken into smaller pieces, retaining the characteristics of the original material. the end result is may small pieces from a single large one. Breaking a rock into smaller pieces increases the surface area available for chemical attack. By breaking rocks into smaller pieces, mechanical weathering increases the amount of surface are available for chemical weathering.

Explain the process of decompression melting

When confining pressure drops sufficiently, decompression melting occurs. decompression melting occurs wherever hot, solid mantle rock ascends, thereby moving into regions of lower pressure. Also occurs when ascending mantle plumes reach the uppermost mantle.

Explain how angular masses of rock often become spherical boulders.

When rocks become extensively jointed, they are chemically weathered on the corners and edges, which gradually become rounded and smooth boulders.

How is magma generated along convergent plate boundaries?

the magma generated in the mantle may change from a comparatively dry, fluid basaltic magma to a viscous andesitic or rhyolitic magma having a high concentration of volatiles as it moves up through the continental crust

What is the geothermal gradient?

the rate of increasing temperature with respect to increasing depth in the Earth's interior

Define Texture

used to describe the overall appearance of a rock based on the size, shape, and arrangement of its mineral grains- not how it feels to the touch. It reveals a great deal about the environment in which the rock formed.