Exam Three Objectives

Igneous Rock

forms from the cooling of magma or lava

- ions slow down, attract and begin mineral formation

Sedimentary rock

Formed from different sediments

Metamorphic rock

A type of rock that forms from an existing rock that is changed by heat, pressure, or chemical reactions.

Basics of the Rock cycle

Magma > crystallization, igneous > weathering, erodes to create sediments > lithification, become sedimentary > metamorphism, become metamorphic from heat and pressure > melting, turns back into magma

Magma Vs. Lava

Magma is molten rock and dissolved gas; lava is molten rock material from which gas has mostly escaped. Magma is formed from decompression melting at ocean ridges, or partial melting of subducting slabs.

Lava

is molten rock material from which gas has mostly escaped

How rocks melt and why

Releasing pressure (allowing molecules to vibrate faster) or heating up material

You are just adding thermal energy to melt.

Decompression Melting

melting due to a drop in confining pressure that occurs as rock rises, also responsible for greatest volume produced, number one way to generate magma.

Partial Melting

the process by which different minerals in rock melt at different temperatures

Igneous rocks are mixtures of minerals, melting occurs over a range of temperatures, produces a magma with a higher silica content than the original rock

Types of melting at different plate boundaries

- Decompression melting - divergent boundary

- Decompression melting and Crustal heating- Continental rift

- Partial melting - Ocean-Ocean and Ocean-Continent Convergent Boundary

How water is added to rocks to lower melting temperature

Adding water lowers melting temperature of rocks.

(think if rocks had water in them, in the crystal structure or in cracks before the rock was submerged) This water when heated would turn to gas/ vaporize. When this happens it changes the pressure in turn causing the melting line to shift.

Mafic

Type of chemistry of the magma, high density magma, melting mantle, produces dark colored rocks

Felsic

Type of chemistry of the magma, low density magma, melting continental, produces light color rocks

Intermediate

Type of chemistry of the magma, melting continental, mix between felsic and mafic and the color falls in between dark and light.

Melting mantle forms

mafic magma

Melting continental crust forms

felsic or intermediate magma

How magma cools

lose heat to air, water, or underlying rocks

conduction into wall rocks

circulating water

loses gases

How magma chemistry can be changed to allow for various rock types from a single magma chamber

As magma cools different minerals crystallize and settle out of solution, overall chemistry of remaining magma changes. Therefore, one original magma may produce several magma types with differing chemical signatures. Magma Differentiation/ Crystallization

Bowen's Reaction Series

different minerals crystallize at different temperatures, a range of temperatures.

Ultra mafic - high temp

Basaltic (mafic) - less high temp

Andesitic (intermediate)- lesser high temp

Granitic (Felsic) - lower temp

(it does not tell you how big the minerals will be, that depends on how fast it cools)

What is the currie point?

500 degrees C

(magic number)

If you start with magma and cool down to below 500c that signature is locked in to the rocks leading to paleomagnetism, however if you heat above 500c the magnetic fields are able to reset.

Other ways to change magma chemistry

Assimilations of country rock into the melt.

Mixing of two magmas as one encounters the other on way to surface.

Xenoliths

an inclusion of unmelted country rock. Other rock types found in a lava flow, mainly found in extrusive rocks. Give clues to underlying geology, diamonds. (Xeno means Alien, Lith means rock// This is the alien rock).

How are igneous rocks classified?

texture, location formed, mineralogy

Igneous textures and what they indicate

(Quick look at the rock, do you see minerals? Can be divided by texture and gives clues as to cooling history)

- Phaneritic Texture - Coarse grained, mineral crystals large enough to see with unaided eye, slow crystallization inside crust

- Aphanetic Texture- Fine- grained, Mineral crystals too small to see without aid of microscope of hand lens, fast crystallization at the surface\

- Porphyritic Texture- Mixed Coarse and fine grained material. Large and small crystals, indicates two phases of crystallization.

Phaneritic

coarse-grained, crystals are large enough to be seen w/out a microscope, formed by slow cooling (intrusive) /// Ex. an oatmeal cookie broken in half, can see the inidividual oats and pieces.

Aphanitic

Rapid cooling at earth's surface results in tiny mineral crystals that can only be seen under a microscope. /// Ex. Vanilla wafer or sugar cookie, overall same and no chunks sticking out.

Porphyritic

rock texture characterized by large, well-formed crystals surrounded by finer-grained crystals of the same mineral. Large crystals are called phenocrysts, smaller crystals are called matrix or groundmass. // Ex. Chocolate chip cookie, Chocolate chips are the phenocrysts, the rest of the cookie would be matrix or groundmass.

Other Igneous Textures

•Pegmatitic

•glassy (Obsidian) - shiny, cools so fast that minerals do not form, or when they do form very microscopic.

•Vesicular (Basalt, Pumice, Scoria) - Rock that has a spongy appearance due to trapped gas bubbles in the lava.

•Pyroclastic

Plutonic vs. Volcanic rocks

Where are they formed and cooled?

Plutonic- are intrusive and formed below the surface

Volcanic- are extrusive and are formed at the surface

Batholiths, sills, dikes

Batholith- single magma chamber, or made up of several magma chambers crossed on each other. The largest plutons.

Sills- magma injected as sheets, not horizontal, normally parallel

Dikes- magma injected as sheets, generally horizontal, cut across

They are intrusive igneous rock formations created when magma cools below the earth's surface.

Classification of Igneous Rocks

Granitic (Felsic), Phaneritic : Granite

Granitic (Felsic), Aphanitic : Rhyolite

Andesitic (Intermediate), Phaneritic : Diorite

Andesitic (Intermediate), Aphanitic : Andesite

Basaltic (mafic), Phaneritic: Gabbro

Basaltic (mafic), Aphanitic : Basalt

Volatiles

Primarily water

Cause rock to melt at a lower temperature

Play an important role in subducting ocean plates

(Other gasses and fluids can be volatile, recall adding water can melt rock at a lower temperature)

- Provide the force to extrude lava

Role of Heat

Earth's natural temperature increases with depth (geothermal gradient) is not sufficient to melt rock at the lower crust and upper mantle

- additional heat is gerated by

friction in subduction zones, crustal rocks heated during subduction, rising, hot mantle rocks

Role of pressure

Increase in confining pressure causes an increase in melting temperature

Drop in confining pressure can cause decompression melting

Lowers the melting temperature

Occurs when rock ascends

Pahoehoe vs. Aa lava

Pahoehoe- resembles braids in ropes -thin and quick. ropy looking, smooth surface, very hot temps. Low viscosity

Aa- rough jagged blocks - ough, jagged blocks, slow moving, cooler temps. high viscosity

Pyroclastic

"fire fragments"

Types of pyroclastic material, they differ based on sizes

- 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

Conduit

or pipe carries gas-rich magma to the surface

Vent

The opening through which molten rock and gas leave a volcano, the surface opening connected to the magma chamber via a pipe

Crater

steep-walled depression at the summit of a volcano

Caldera

a large depression typically caused by collapse or ejection of the summit area of a volcano, a summit depression greater than 1 km diameter

Shield Volcano

a broad, domed volcano with gently sloping sides, characteristic of the eruption of fluid, basaltic lava.

generally large size

e.g. Mauna Loa in Hawaii

Cinder Cone

smallest, built from ejected lava fragments, steep slope angle, frequently occur in groups

Strato Volcano

Most are adjacent to the Pacific Ocean (e.g. Mt. Rainer, Mt. st. helens, mt. vesuvias, etc)

Large size

Interbedded lavas and pyroclastics

Most violent and deadly type of activity

Eruption Column

buoyant plumes of hot ash-laden gases that can extend thousands of meters into the atmosphere, Large vertical column of ash, gasses, rock, and debris above an erupting volcano.

nuee ardente

Eruption column often produce nuee ardente

- fiery pyroclastic flow made of hot gases infused with ash, flows down sides of a volcano at speeds up to 200 km (125 miles) per hour

Incredibly dangerous!!

Columnar Jointing

A type of fracturing that yields roughly hexagonal columns of basalt; columnar joints form when a dike, sill, or lava flow cools.

Caldera and Fissure Eruptions

Caldera: steep walled depression at the summit, formed by collapse, nearly circular, size exceeds one kilometer in diamerter

Fissure: fluid basaltic lava extruded from crustal fractures called fissures (e.g. columbia plateau)

Relationship of plate boundaries to location of volcanoes

Most volcanoes are located on the margins of the ocean basins (intermediate, andesitic composition) (ocean-ocean, ocean- continental) - Convergent boundary

Second group is confined to the deep ocean basins (basaltic lavas)- Divergent boundary

Third group includes those found in the interiors of continents/plates (hotspots, hawaii, yellowstone

Factors affecting the explosivity of eruptions

Composition of the magma, the more silica you have increases explosivity

Temperature of the magma, cooler magmas are already slowing down and is harder for gas to escape, so hotter is more explosive

Dissolved gases in the magma, the more gas you have the more explosive the volcano

Viscosity and how it affects eruptions

Viscosity is a measure of a material's resistance to flow.

Ex. water has a viscosity of 1 and has no problem moving, honey however has a higher viscosity. It is more resistant to moving.

More viscous: difficult to flow and traps gas

Less viscous: flows easier and gas can escape

Role of gasses in driving eruptions

Propels eruption and forms ask, under less pressure, gas forms bubbles, dissolved gas held in magma by pressure.

Types of eruption materials

Lava flows: basaltic lavas are more fluid, there are two types (Pahoehoe and Aa lava)

Gases: One to five percent of magma by weight, Mainly water vapor and carbon dioxide

General parts of a volcano

Conduit, vent, crater, caldera

Three types of volcanoes and how dangerous each type is for humans

Shield volcano (generally less lethal), Cinder cone (small but explosive violent) , Stratovolcano (most dangerous)

Lahar, Volcanic Necks, Domes

1. Lahar- volcanic mudflow

2. Volcanic necks- Made of magma that hardened in the volcano's central conduit and was exposed by erosion

3. Domes- highly dangerous, rounded, steep-sided mounds formed by viscous magma;explosive eruptions. Grow from the inside as magma is injected into interior of dome, grow as magma breaks through surface. (scab like)

Famous eruptions and volcanoes

Mount St. Helens, Krakatau, Pinatubo, Mt. Unzen, Fujiyama, Popocatepeti, Paricutin, Vesuvius (pompeii), Santorini, Pelee

How volcanoes are monitored

Increased seismic activity

Increased gas activity

Changes in topography

Changes in temperature

Difference between active, dormant, and extinct volcanoes

General terms describing activity

extinct- no source of magma, will never erupt again

dormant- means were active in the past, yet not active recently (haven't been active in the last 2-4 hundred years)

active- source of magma, have had activity recently

Difference between weathering, mass wasting, and erosion

Weathering- The disintegration and decomposition of material at or near the surface

Mass wasting- the transfer of rock material downslope under the influence of gravity

Erosion- The process by which wind, water, ice, or gravity transports soil and sediment from one location to another///the incorporation and transportation of material by a mobile agent, usually water, wind, or ice.

Two types of weathering

mechanical (physical) and chemical

How joints affect weathering

Cracks or fractures in the rock, joints have no movement.

They are important because they allow entry into the inside of the rock. They create pathways for water, air, or roots.

- pre existing joints, expansion joints, unloading

Mechanical Weathering

Breaking of rocks into smaller pieces

main types: frost wedging (water seeping in), unloading, biological activity6

Chemical weathering

alters the internal structures of minerals by removing or adding elements.

Most important agent is water, oxygen dissolved in water oxidizes materials, carbon dioxide (CO2) dissolved in water forms carbonic acid and alters the material.

Conditions which affect chemical weathering: High temperatures that acceelerate reactions, consistent moisture (rainwater) as a solvent, acidic conditions, and broken rock surfaces that provide more surface area. (Climate, Presence of water, Acidity and Carbon dioxide, Vegetation and organism)

Conditions affecting weathering rates

Advanced mechanical weathering aids chemical weathering by increasing the surface area.

Important factors- rock characteristics (mineral composition and solubility, physical features such as joints)

Primary Factor: climate, rock composition, and surface area exposure.

* Temperature and moisture are the most crucial, chemical weathering is most effective in areas of warm temperatures and abundant moisture

Differential Weathering

caused by variations in composition, creates unusual and spectacular rock formations and landforms

Regolith vs. Soil

Regolith: the layer of rock and mineral fragments that nearly everywhere covers Earth's surface

Soil: (has to have organic materials) Soil is a combination of mineral matter, water, and air- supports the growth of plants. portion of the regolith.

All soil is part of the regolith, not all regolith is soil.

Loam

Residual vs. transported soils

Soil horizons and their characteristics

Solum and topsoil

Basics of soil erosion and activities that threaten soils

Weathering and ore deposits

Slope stability and angle of repose

Triggering mechanisms for mass wasting events

How mass wasting events are classified

Debris avalanches, creep, and solifluction

basic parts of a mass wasting event (scarp, toe, etc.)

Granular vs slurry flows

How frost heaving helps creep