Earth Science Test 3 : Igneous Rocks or Something Like That

Three major types of volcanoes (their formation, size, characteristics, and eruptive style),

1. shield volcano - broad, slightly domed shape - composed primarily of basaltic lava - generally cover large areas - produced by mild eruptions of large volumes of lava - largest volcanoes on earth examples: Kilauea, Mauna Kea and Moana Lou 2. cinder cone - built from ejected (mainly cinder-sized) pyroclastic fragments and lava - steep slope angle - rather small size - frequently occurs in swarms/groups examples: Paricutin, AZ 3. composite cone or stratovolcano - many volcanoes of this type are located adjacent to the Pacific rim (ring of fire) - form large, symmetrical volcanoes 1000's of feet high and several miles wide at their bases - volcanic cones composed of interbedded lava flows and layers of pyroclastic debris - magmas typically rhyolitic or andesitic in nature and, as a result, the viscous magmas usually travel short distances downslope - most explosive type of volcano

What factors determine explosiveness of a volcanic eruption

Composition, temperature, and dissolved gases A more viscous (thick) magma will produce a more violent eruption. This is controlled in part by the concentration of silica in the magma. A magma with low silica (<45%) will be runny and so the eruption will not be explosive. A magma with high silixa (>60%) will be quite viscous and so the eruption will be more violent. The temperature of the magma is also a factor. A hotter magma will be less viscous One other factor is the amount of dissolved volatiles in the magma (chlorine gas, water, and other gases). A magma with a lot of dissolved gases will form a lot of large bubbles. It is the bursting of these bubbles that causes an eruption to be explosive, so the more volatiles in the magma, the more violent the eruption

Describe igneous activity wrt plate margin type (convergent, divergent, intraplate) as well as intraplate settings and examples.

Convergent Similar to throwing salt on a sidewalk to melt ice • Descending plate partially melts • Magma slowly rises upward • Rising magma can form- Volcanic island arcs in an ocean (Aleutian Islands) - Continental volcanic arcs (Andes Mountains) Divergent • The greatest volume of volcanic rock is produced along the oceanic ridge system - Lithosphere pulls apart- Less pressure on underlying rocks- Partial melting occurs- Large quantities of fluid basaltic magma are produced Intraplate Activity within a rigid plate • Plumes of hot mantle material rise • Form localized volcanic regions in overriding plate called hot spots - Produces basaltic magma sources in oceanic crust (Hawiian Islands, and Iceland) - Granitic (Yellowstone) and basaltic (Columbia River Plateau) magma sources in the northwestern United States

Be able to list and describe volcanic landforms (intrusive igneous structures) other than volcanic cones and how classified with respect to shape and orientation.

Emplacement of magma • Magma at depth is much less dense than the surrounding rock - Increased temperature and pressure causes solid rock to deform plastically - The more buoyant magma pushes aside the host rock and forcibly rises in the Earth as it deforms the "plastic" host rock Most magma is emplaced at depth An underground igneous body is called an intrusion or pluton Plutons are classified according to: - Shape• Tabular (sheet-like) • Massive - Orientation with respect to the host (surrounding) rock Discordant - cuts across existing structures Concordant - parallel to features such as sedimentary strata • Types of igneous intrusive features Dike - a tabular, discordant pluton Sill - a tabular, concordant pluton • e.g., Palisades Sill, NY • Resemble buried lava flows • May exhibit columnar joints • Types of igneous intrusive features - Batholith• Largest intrusive body • Often occur in groups• Surface exposure (>100 sq km)• smaller bodies (< 100 sq km) are termed stocks • Frequently form the cores of mountains

MATCHING Largest eruption ever known based on tephra deposits

Eruption of Yellowstone

Four major compositional types (felsic, mafic, intermediate, ultramafic) of igneous rocks (along with textures) of igneous rocks and be able to give and describe examples.

Granite (felsic) rocks - igneous rocks of granitic composition are made up almost entirely of light-colored silicates - quartz and potassium feldspar (felsic) - coarse-grained (phaneritic) - granite - rhyolite is the extrusive (aphanitic) equivalent of granite - obsidian's chemical composition is similar to felsic rock Obsidian is a natural volcanic glass Pumice is a vesicular volcanic glass Basaltic (mafic) rocks - contain substantial dark silicate minerals and Ca - rich plagioclase but no quartz - most common extrusive igneous rock - dark green to black, fine-grained - contains pyroxene, olivine, and plagioclase feldspar - scoria and basalt is an example Andesitic (intermediate) rocks - falls between granitic and basaltic composition - mixture of both light and dark-colored minerals - amphibole and plagioclase feldspar - coarse-grained intrusive equivalent is diorite - andesite and diorite Ultramafic rocks - contain mostly dark-colored minerals - olivine and pyroxene - ex: peridotite and dunite

How does cooling rate affect the texture of igneous rocks

Igneous Rock Textures, Coarse-Grained - slow cooling results in the formation of large crystals. Igneous rocks with large crystals exhibit a coarse-grained texture Igneous Rock Textures, Fine-Grained - rapid cooling of magma or lava results in rocks with small, interconnected mineral grains. Igneous rocks with small grains are said to have a fine-grained texture

Know the two main types of igneous rocks (intrusive/extrusive) and examples

Intrusive Rocks : when magma never reaches the surface so it solidifies - may be exposed at the surface by uplift and erosion Examples : - Mount Rushmore - Stone Mountain - Mount Rushmore and the Black Hills - Yosemite National Park

Compare and contrast the eruption style of Kilauea Vs Mount St. Helens (and why they behave differently-factors affecting explosiveness of volcanic eruptions)

Kilauea - shield volcano - most active volcano in Hawaii - large, fairly recently formed caldera at its summit and two active rift zones - one extending 125 km east and the other 35 km west - lava intermittently pours into the sea, adding new land to the island of Hawaii Mount St. Helens - composite cone or stratovolcano - a 160 sq mile area to the north of the mountain were flattened and stripped of their branches by the force of the blast - accompanying mudflows carried water - the eruption ejected nearly 1 km cubed of ask and rock debris as high as 18 km (11 miles) into the stratosphere - ash in the immediate vicinity exceeded 2 meters (6 ft) in depth - measurable deposits were reported in Oklahoma and Minnesota and crop damage occurred as far away as central Montana

Major geologic hazards associated with volcanic activity and notable examples of where occur MATCHING

Kilauea - erupting since 1983 Mauna Kea - tallest mountain on earth Paracutin - cinder cone eruption in cornfield

MATCHING African volcano emitted large CO2 cloud which killed 1700 people and 3500 livestock

Lake Nyos

MATCHING 1783 Icelandic eruption released large quantities of HF and sulfur dioxide leading to famine and deaths of livestock and over 30,000 people in Great Britain and NW Europe

Laki Iceland Eruption of 1783-84

MATCHING 1883 eruption generated tsunami which claimed est 36,000 lives

Mount Krakatoa Indonesia Eruption of 1883

MATCHING Violent eruption in 1815 associated with the "year without a summer" and the potato famine in Ireland

Mount Tambora Indonesia Eruption of 1815

MATCHING Cities surrounding this Japanese volcano utilize lahar diversion control ditches

Mt. Unzen, Japan

What type of volcanic material is indicative of eruption under water?

Pillow lavas

The magnitude of historical eruptions can be measured by the___________.

Volcano Explosivity Index

Mount Pelée on the island of Martinique killed thousands of people in ________.

a caldera collapse

Which of the following rocks exhibits aphanitic texture?

andesite and rhyolite

The crystallization of a mafic magma will generate the following rock type:

basalt

Volumetrically, most lava on earth is of a(n) ________ composition.

basaltic

The Sierra Nevada of California is composed primarily of this igneous structure.

batholith

Paricutin is an example of a ________.

cinder cone

Which of the following volcano types are short lived volcanos that last a few days to months and then shut down?

cinder cone

When large masses of magma solidify far below Earth's surface, they form igneous rocks that have a ___________.

coarse-grained texture

Stratovolcanoes are commonly found at ________.

convergent plate boundaries

The Columbia Plateau in the northwestern United States is an excellent example of ________.

flood basalts

Know and describe the materials extruded during an eruption : gases (types)

gases - mainly water vapor and carbon dioxide - one to six percent of magma by weight - smaller, variable quantities of sulfur dioxide (SO2), hydrogen sulfide (H2S), fluorine gas (F2), hydrogen fluoride (HF), and other gases may also be emitted depending on magma composition - includes water vapor, carbon dioxide, sulfur dioxide, and hydrogen sulfide - H20, CO2, SO2, H2S - gases expand near the surface - expanding gases can propel lava hundreds of meters into the air, producing lava fountains dissolved gases (volatiles) - mainly water vapor and carbon dioxide - gases expand near the surface - provide the force to extrude lava - violence of an eruption is related to how easily gases escape from magma - easily escape from more fluid magma - more viscous magma produces a more violent eruption

Obsidian exhibits a ________ texture.

glassy

The phaneritic igneous rock which is composed mainly of quartz and potassium feldspar is _______.

granite

The igneous activity in Yellowstone National Park is associated with what tectonic setting?

intraplate setting

As the temperature of lava increases, ____.

its viscosity decreases

A ________ is a near surface, intrusive igneous rock body that results from local inflation of a horizontal sill.

laccolith

Know and describe the materials extruded during an eruption : lava flows (types and settings)

lava flows - deaths by lava flow are rare bc it moves so slow - two basic types of magma: mafic and felsic - mafic (basaltic) lava are more predominant (90%) - mafic lavas are very liquid (30 to 1000 feet per hour flow rate) compared with movement of silica rich lavas which may be too slow to perceive - types of Basaltic lava - Pahoehoe lava (resembles braids in ropes) - Aa lava (rough, jagged blocks) - Texture depends on whether or not the flow develops a solid surface before it stops moving mafic lava flows - recall that much of Earth's volcanic output occurs along ridges - when outpourings of mafic lava occur on the ocean floor, the flow's outer skin quickly freezes to form volcanic glass - the interior lava is able to move forward by breaking through the hardened surface - this process occurs over and over, as molten basalt is extruded - like toothpaste from a tightly squeezed tube - this result is a lava flow composed of numerous tube - like structures called PILLOW LAVAS, stacked one atop the other - slide 38 & 39 felsic lava flows - the higher silica content and lower temperature of felsic melts yield higher viscosity lavas which do not flow far from the vent - a bulbous mound, called a LAVA DOME, typically solidifies within the vents of felsic volcanoes following an eruptive period

Highly explosive volcanoes tend to have what type of magma?

magma with high silica, high viscosity, and higher gas content

Which of the following is NOT considered to be a pyroclastic material?

pahoehoe

Know and describe the materials extruded during an eruption : pyroclastic materials ( types and how classified)

pyroclastic materials - "Fire Fragments" - aka "airfall deposits" or "tephra" types of pyroclastic material - ash and dust - fine, glassy fragments - pumice - from "frothy" lava - lapilli - "walnut" size - cinders - "pea-sized" particles larger than lapilli - blocks - hardened lava - bombs - ejected as hot lava

The most important factor affecting the texture of an igneous rock is __________.

rate of cooling

What is the Volcanic Explosivity Index (VEI)- what does it measure and how it is calculated.

rating based on volume of erupted tephra

Which list places the magma types in order of decreasing viscosity (most viscous listed first)?

rhyolitic, andesitic, basaltic

Magma tends to rise towards Earth's surface primarily because ____.

rocks become less dense when they melt

A magma's viscosity is directly related to its __________.

silica content

A ____________ is a tabular, concordant pluton.

sill

The classification of igneous rocks is based on _____________.

texture and mineral composition

Why can two igneous rocks have the same minerals but different names?

the rocks may have different textures

Know Bowens reaction series (be able to list/draw) and how it relates to compositions VS temperatures (and eruption explosiveness) of igneous rocks and magmatic differentiation and crystal settling.

the sequence in which the minerals form not all of the minerals in a melt crystallize at the same time or temperature When a magma begins to cool/crystallize, any mafic minerals such as olivine and pyroxene crystallize first, followed by amphiboles. Micas, quartz, and potassium feldspar are the final minerals to crystallize