Geology Exam 1 2

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Geology: science pursuing an understanding of Earth
Physical Geology: examines materials composing Earth to understand processes that operate beneath and on its surface
Aspects of geology affecting people: (1)Natural Hazards
[flood, earthquake, volcano, landslides]

(2)Natural Resources
[oil & gas, metals, coal/uranium, gravel/sand, H20]
Geologic time scale: -Billions of years

-reoccurance normally longer than human life span

-100 million yrs ago = recent

-rock sample 10 million yrs old = young
Science assumes...: the natural world is consistent and predictable
Goal of science...: discover patterns in nature to make predictions from
Science collects facts through..: observation & measurement
The Earth system is powered by: (1) The Sun
---drives external processes [climate, erosion]

(2)Earth's interior.

-a-heat remaining from its formation
-b-heat still generated by radioactive decay
(powers the interal processes that make volcanos/earthquakes/mountains)

-Earth convects like a boiling pot exchanging heat from inside to surface
plate tectonics are driven by: convection of the mantle
Greater size of planet = slower loss of heat [relating to earth/mars?]: Earth is still shedding heat

Mars = smaller = already lost internal heat
=never convected = no plate techtonics = 1 LARGE volcano rather than multiple small volcanos
3 main rock types: IGNEOUS

SEDIMENTARY

METAMORPHIC
The Rock Cycle shows:: the cycles in which rocks change into other rocks

shows processes that materials change on the surface & inside of earth
Earth is ___ yrs old: 4.5 billion
Geologic time scale made by:: first fossils

then given actual numbers using radioactive dating
Origin of Earth: 1. big bang
(larg explosion sending all matter of universe flying outward at high speed)

2. debris (mostly H and He) colled/condensed into first stars/galaxies
---in our galaxy=milky way=our solar system formed

3. Nebular Hypothesis

*earth & other planets formed from same material as sun

4. Layered structure of earth developed

5. dense material moves to center of earth... light material stays at shallow levels
Earth's Layers: -iron rich core
-the mantle (largest layer)
-thin primitive crust
Formation of Earth's core: -intense heating due to radioactive decay
-causes iron and nickel to melt
-dense liquid metal sank toward center of planet
Formation of Earth's Mantle: -same early heating formed buoyant masses of molten rock
-light molten rock rose toward surface
-solidified to form primitive crust
*enriched in O2
Earth's internal layers can be defined by:: 1) chemical composition

2) physical properties
Earth's Layers Defined by Chemical Composition:: 1)Crust
2)Mantle
3)Core
Earth's Layers Defined by Physical Properties: 1) Lithosphere (crust & uppermost mantle)
[acts like brittle solid]
2) Astehnosphere
[acts like plastic solid]
3) Mesosphere (lower mantle)
4) Core (outer & Inner)
Chemical Comp. of Crust: 1)oceanic crust
-composed of igneous rock (BASALT)

2)continental crust
-many rock types (upper=mostly granitic, lower=mostly basalt)
Chemical Comp. of Core: -iron nickel alloy (mix)
-minor amts of O2, silicon, & sulfur (form compounds easily w/ iron)
Physical Prop. of Lithosphere: -consists of crust and uppermost mantle
-cool rigid shell (cool=strong=rigid)
Physical Prop. of Asthenosphere: -in upper mantle
-soft, comparatively weak to lithosphere
-has a small amt of melting
-mechanically detached from lithosphere = *the lithosphere can move independently of asthenosphere*
-acts like plastic solid
Physical Prop. of Lower Mantle (mesosphere): -increased pressure counteracts high temps
=rocks gradually strengthen with depth
-rigid strong, but still hot and capable of gradual flow
Physical Prop. of Core: 1)outer core
- liquid layer
- convective flow of metallic iron
=generates magnetic field

2)inner core
-high temps but stronger than outer core due to immense pressure
-behaves like a solid
Moon: Made up of same rocks as Earth

About the same age as Earth
Formation of Moon: -impact of mars-size planet w/early earth
-ejected debris entered orbit around earth
-condensed to form moon
*ejecterd material mostly iron-poor mantle & crustal rocks == small iron core on moon
Terrestrial v Jovian planets: Terrestrial:
-small
-inner planets
-Mercury Venus Earth Mars
-rocky
-minor ice
-minor gas
== meager atmospheres

Jovian:
-Large
-Outer planets
-Jupiter, Saturn, Uranus, Neptune
-gases (hydrogen, helium)
=thick atmospheres
-ices (water, amonia, methane)
Escape Velocity: the speed a gas molecule can evaporate from a planet

-bigger planets = higher escape velocities = difficult for gas to evaporate from them

-moon unable to hold gases = lack of atmosphere
====no weatering/erosion
Earth has less craters than moon: bc of Earth's greater atmosphere

friction [in earth's atmosphere] burns up small debris before it hits the ground
ejecta: ejected material from crater when meteoroid strikes
Earth v. Mars: both terrestrial planets

Mars:
-smaller
-atmosphere is 1/100 density of earth's atmosphere
-polar caps = water ice covered by frozen carbon dioxide
-lost heat early in history
====mantle never convected
====no plate tectonics
====all heat lost through one place
====gigantic volcano [ex. mons olympus]
-lost magnetic field and atmosphere
====less erosion
Reasons for Mars' giant volcanos: -lost heat early in history
[no plate tectonics=heat lost in one place]

-smaller than earth
[less gravity=longer til gravity pulls down volcanos]
Jarosite: found on earth and on mars
Meridiani landing site on mars [possible life?]: Bedrock is exposed in shallow craters, suggesting that this part of Mars is covered by only a very thin layer of windblown deposits -and it may be relatively easy to observe and analyze underlying rocks.

Rock outcrops or soil may contain insitu hematite -helping to explain its origin

Evidence for hematite in volcanic or hot-spring deposits
may be a great place to look for evidence of past life (e.g. fossils).
Mineral: IT MUST

1) Occurs naturally

2) Inorganic Solid

3) Possess orderly internal structure
[atoms must be arranged in a definite pattern]

4) Definite Chemical Composition
Rock: Solid aggregate (minerals joined so properties of each are maintained) mass of minerals
Mineral's ordered internal structure means...: every sample of the same mineral contains the same elements joined together in a pattern
Elements atomic structure:: nucleus contains protons = # of nuetrons

electrons surround nucleous
-located in shells (energy levels)
Atomic # determined by: # of protons

-atoms w/same atomic # = same element
Element definition: collection of electrically neutral atoms with the same atomic number
Valence Electrons: Outermost electrons

-the ones involved in chemical bonding
Chemical Bonding: formation of a compound by combining 2+ elements

1.Ionic*
2.Covalent*
*usually occur together
3.Metallic
Ionic Bonding: gain/loose valence electrons to form ions
-after electron transfer, atoms no longer electrically neutral
-*aka* the attraction of oppositely charged ions to one another making a neutral compound

[Ions=atoms with an electrical charge
-anion (- atom)
-cation (+ atom)]

[ionic compounds=arrangement of oppositely charged ions
*internal atomic arrangement of minerals determined by size of ions]
Covalent Bonding: -atoms share electrons to gain neutrality
-covalent compounds stronger than ionic compounds
Metallic Bonding: Valence electrons free to migrate among atoms
-weaker & less common than covalent/ionic
mass #: Nuetrons + Protons
Isotope: atom with variation in mass #

-same # protons
-varying # nuetrons

**can have unstable nuclei that emit particles/energy
= RADIOACTIVE DECAY
[clock for earth's history]
Polymorph: Minerals with same chemical compositions but different cystalline structures

*2 minerals with same chemical comp can be joined together in different ways
==2 minerals w/different properties can have the same chemical comp.

-ex. diamond & graphite
{both polymorphs of carbon}
=both consist of carbon
=difference = how they were formed
[diamonds=compact, formed at greater depth
graphite=widely spaced, weakly held together]
*heating graphite under high pressure can make diamonds
*peanut butter in high pressure can make diamonds
The ordered atoms in a mineral form a particular crystalline structure. The internal atomic arrangement is determined by:: -charges of the ions

-size of the ions involved
Physical properties of minerals (list): 1) Crystal Form
2) Luster
3) Color
4) Streak
5) Hardness
6) Cleavage
7) Fracture
8) Specific Gravity
9) Other
CRYSTAL FORM physical property: External expression of ordered internal arrangement of atoms

-crystal growth can be interrupted by not enough space or rapid heat loss

*not cleavage
LUSTER physical property: appearance of mineral in reflected light

-1-metallic
(have appearance of metal, regardless of color)
-2-non-metallic

-other: oily, silky, earthy
COLOR physical property: unreliable

highly variable for a given mineral due to slight variance in chemistry
STREAK physical property: color of mineral in powdered form

-helpful in determining different forms of same mineral
HARDNESS physical property: resistence of mineral to scratching

-determined by rubbing mineral with unknown hardness against one of known hardness

-compared on a standard scale:
MOHS SCALE OF HARDNESS
[10 minerals arranged in relative ranking from 1(softest-talc) to 10(hardest-diamond)]
CLEAVAGE physical property: tendancy to break along bonds

-produces flat, shiny surfaces
-described by resulting shapes (# of planes, & angles joining planes)

*no cleavage called fracture
FRACTURE physical property: absence of cleavage when mineral's broken

*quartz
SPECIFIC GRAVITY physical property: ratio of weight of mineral to equal volume of water

-avg value = 2.7
-hefting mineral can work too
(comparing weight of mineral in hand to common rocks)
OTHER physical properties: -magnetism
-reaction to hydrochloric acid
-malleability
-double refraction
(transparent mineral over printed material makes words appear twice)
-taste
-smell
-elasticity
Conchoidal Fracture: minerals that break into smooth curved surfaces resembling broken glass
Rock-Forming Minerals: common minerals that make up most of Earth's Crust

-8 main elements making up 98% of Crust
8 main elements in crust:: 1)Oxygen
2)Silicon
3)Aluminum
4)Iron
5)Calcium
6)Sodium
7)Potassium
8)Magnesium
Silicates: -most important mineral group
-most of rock forming minerals are silicates
-abundant bc large amt of silicon & O2 in earth's crust
-basic building block =
SILICON-OXYGEN TETRAHEDRON molecule
===4 oxygen ions surrounding smaller silicon ion
Different Silicate Structures (how silicon-oxygen tetrahedrons are joined): -isolated tetrahedra
-ring structures
-single chain structures
-double chain structures
-sheet structures
-layered structures
-complex 3D structures
AMPHIBOLE GROUP silicate mineral: -double chain
-cleavage: perfect cleavage; 124 & 56 degree angles
-Bonded by variety of ions

***HORNBLENDE***
-dark green-->black
-similer in appearance to augite (except for cleavage
MICA GROUP silicate mineral: -sheet structures
-cleavage: sheet structures result in one direction of perfect cleavage (one plane)

***BIOTITE***
-common dark colored mica
-shiny, black
-iron rich

***MUSCOVITE***
-common light colored Mica
FELDSPAR GROUP silicate mineral: -3D structure
-cleavage: perfect cleavage: 2 planes at 90 degrees
-most common mineral group

***Orthoclase (potassium feldspar)***
-contains potassium
-light cream -->salmon color
***Plagioclase (sodium & calcium feldspar)
-white->gray color
QUARTZ silicate mineral: -3D structure
-NO cleavage
-consists entirely on silicon & oxygen
-light colored (varies)
-light weight
-**6 sided shape**
-develop pyramid shaped ends
Clay Minerals (still silicates): clay= general term to describe variety of minerals
-all have sheet structure
-originate from chemical weathering
important NON-SILICATE MINERALS: -oxides
-sulfides
-sulfates
-native elements
-carbonates
-halides
-phosphates
CARBONATES non-silicate minerals: primary constituents in limestone & dolostone

***Calcite
***Dolomite
Non-silicate minerals w/ economic value: -Hematite
(oxide mined for iron ore)
-Halite
(halide mined for salt)
-Sphalerite
(sulfide mined for zinc)
-Native Copper
(native element mined for copper)
Igneous Rocks: form as molten rocks cool/solidify
Characteristics of Magma (molten rock): -parent material of igneous rocks
-forms from partial melting of rocks in earth

*called lava only when reaches surface
Extrusive / Volcanic Rocks: rocks formed from lava at surfacee
Intrusive / Plutonic Rocks: rocks formed from magma that crystallizes at depth
[ex. Granite]
3 Components of Magma: 1)MELT: liquid portion (mobile ions of elements from crust-mostly silicon & oxygen)
2)SOLIDS:(if any)silicate minerals that have already crystallized
3)VOLATILES:gases dissolved in melt [H20, carbon dioxide, sulfur dioxide]
Crystallization of Magma: as magma cools ions in the melt loose their mobility & arrange themselves in an ordered crystalline structures
(normally O2 and silicon link together first
Igneous Rocks are Classified by: 1. Texture
(size/shape/arrangement of interlocking crystals)
2. Mineral Composition
Factors Contributing to Texture of Igneous Rocks: 1) the rate magma cools
-slow cooling = fewer & Larger crystals
-fast rate = many small crystals
-very fast rate = glass (no time for ions to arrange=unordered ions=glass)

2) amount of silica present

3) amount of dissolved gases in the magma
Types of Igneous Textures: 1)Alphanitic (fine grained)
2)Phaneritic (coarse grained)
3)Porphyritic
4)Glassy
5)Pyroclastic (fragmental)
6)Pegmatitic
APHANITIC igneous texture: -fine grained texture
-rapid rate of cooling of lava or magma
-microscopic crystals
-can contain Vesicles [holes from gas bubbles]
PHANERITIC igneous texture: -coarse grained texture
-slow cooling
-crystals identified w/o microscope
-ex GRANITE
POPHYRITIC igneous texture: -minerals form at different temperatures & different rates
-Large crystals [PHENOCRYSTS] are embedded in a matrix of smaller crystals [GROUNDMASS]
GLASSY igneouos texture: -very rapid cooling of igneous rock
-OBSIDEAN=resulting rock (arrowheads)
PYROCLASTIC igneous texture: -various fragments ejected during violent volcanic eruption
-superheated/superfast flows
-appear similar to sedimentary rocks
PEGMATITIC igneous texture: -exceptionally coarse grained
-forms in late stages of crystallization of granitic magmas
-VERY Large crystals
Dark (ferromagnesian*) Silicate Minerals that Igneous Rocks are Composed Of: -olivene
-pyroxene
-amphibole
-biotite mica

*ferromagnesian=contain Fe or Mg in structure & are heavier
Light Silicate Minerals that Igneous Rocks are Composed of: -Quartz
-Muscovite Mica
-Feldspars

*not much Fe & Mg
Granitic v Basaltic Composition of Igneous Rocks: 1)Granitic:
-light colored silicates
-"felsic" (feldspar & silica in composition)
-high amounts of silica
-major part of earth's crust

2)Basaltic
-composed of dark silicates & feldspar
-"mafic" (magnesium & ferrum {iron} in composition)
-more dense than granitic
-make up ocean floor & many volcanic islands
GRANITE igneous rock: -Granitic (felsic)
-phaneritic
-65% quartz
-25% feldspar
-abundant
-associated with mountiain building
-"granite" covers many different mineral compositions

-pink & coarse-grained
RHYOLITE igneous rock: -GRANITIC (Felsic)
-extrusive equivalent to granite [granite that made it to the surface]
-alphanitic texture
-less common than granite
-phenocrysts (large crystal embedded in matrix can be quartz or feldspar)
BASALT igneous rock: -BASALTIC (mafic)
-volcanic origin
-alphanitic texture
-composed mainly of pyroxene & plagioclase feldspar
-most common extrusive igneous rock
GABBRO igneous rock: -BASALTIC (mafic)
-intrusive equivalent to basalt
-phaneritic texture of pyroxene & plagioclase
-makes up a lot of oceanic crust
OTHER COMPOSITIONAL GROUPS OF IGNEOUS ROCKS (other than granitic & basaltic): 1) Intermediate (Andesitic) Composition
-25+% dark silicate minerals
-associated with explosive volcanic activity

2)ULTRAMAFIC Composition
-rare
-high in Fe & Mg
-composed entirely of ferromagnesium silicates
ANDESITE igneous rock: -INTERMEDIATE (andesitic) composition
-volcanic origin
-alphanitic texture
-resembles rhyolite
DIORITE igneous rock: -plutonic (deep magma origin) equivalent to andesite
-coarse grained
-intrusive
-made up of intermediate feldspar & amphibole
Silica Content Changes Magma's Behavior GRANITIC V BASALTIC MAGMA: 1)Granitic Magma
-high silica content==
==more viscous (=thicker)==
==usually lose mobility before reaching surface
==tend to produce large plutonic structures (rocky mtn nat'l park, pikes peak)
-still liquid at low temps (700 C)
-goes BOOM when erupts
-[Yellowstone]

2)BASALTIC MAGMA
-low silica content
-fluid-like behavior
-crystallizes at high temps
-Gurgles when it erupts
-[Hawaii]
OBSIDIAN igneous rock: -GRANITIC (felsic)
-dark colored
-glassy texture
-usually when lava's put out quickly
PUMICE igneous rock: -GRANTIC (felsic)
-volcanic
-glassy texture
-frothy appearance (extrusive foam)
-usually found with obsidian
-formed when large amts of gas escape through lava (generates gray frothy mass)
-many samples float in water
PYROCLASTIC ROCKS: composed of fragments ejected during volcanic eruption
-2 types of pyroclastic rock:

1)Tuff
-ash sized fragments

2)Volcanic Breccia
-particles larger than ash
Geothermal Gradiant: Change in Temperature with Depth

-rate of temp change avgs at 20-30 C per Kilometer
Origin of Magma: originates by rocks melting in earth's mantle
-since mantle is made of mostly solid rock, magma is formed when rocks are raised above their melting point.

-rocks are raised above their melting point by:
1)added heat
2)decrease in pressure
3)introduction of volatiles
Heat's role with Magma: -rocks in lower crust/upper mantle are near melting points
-rocks lowering into mantle or heat rising from mantle helps induce melting
Pressure's role with Magma: -melting occurs at higher temperature due to pressure

-when pressure drops enough "Decompression Melting" is triggered
==[rock can ascend into lower pressure areas]===responsible for magma at plate bounderies
Volatile's role with Magma: volatiles (gas components of magma)---USUALLY WATER---
Cause rocks to melt at LOWER temperature

-effect of volatiles magnified by increasing pressure

-volatiles play important role where cool slabs of oceanic crust lower into mantle
Melting & Crystallization of Magma temperature range: Both span a great temperature range of about 200 C
Processes Responsible for Different Magma Compositions (and thus wide variety of igneous rocks): 1)Magmatic Differentiation
2)Assimilation
3)Magma Mixing
4)Partial Melting
MAGMATIC DIFFERENTIATION {changing magma composition}: **WHEN 2+ SECONDARY MAGMAS FORM FROM A SINGLE PARENT MAGMA**

because minerals crystallize at different temps
a seperation of solid and liquid in magma can occur
-this happens when earlier formed crystals are denser than the liquid magma

-the solid crystals sink to the bottom of magma chamber
-when the remaining melt solidifies it will have a much different chemical composition from the first solid crystals & the parent magma
ASSIMILATION {changing magma composition}: **CHANGING A MAGMA'S COMPOSITION BY THE INCORPORATION OF FOREIGN MATTER (surrounding rock bodies) INTO A MAGMA**
MAGMA MIXING {changing magma composition}: **TWO BODIES OF MAGMA INTRUDING ONE ANOTHER**

-2 chemically distinct magmas can produce a composition much different from the either original magma
PARTIAL MELTING {changing magma composition}: **INCOMPLETE MELTING OF ROCK**

since the melting of rocks has such a great temp range
minerals with lowest melting temps are first to melt.
-as melting continues magma approaches the composition of the rock it was derived from
-most of the time complete melting, however, does not occur
Formation of Andesitic Magmas From Partial Melting: -interactions between basaltic magma & silica-rich parts of earth's crust generate andesitic magma
(ex. basaltic magma migrates up & melts/assimilates crustal rocks it ascends through)

-Can also form from magmatic differentiation
(as basaltic magma solidifies the silica-poor minerals crystallize first.
=the remaining melt (now enriched in silica) has an Andesitic Composition
[secondary magma]
Formation of Granitic Magmas From Partial Melting: -likely to form as the end product of the crystallization of andesitic magma (magmatic differentiation)
-or partial melting of silica rich continental rocks
Factors that determine violence/explosiveness of Volcanic Eruption: The viscosity determines the violence which is determined by:

1)Composition of Magma
2)Temperature of Magma
3)Dissolved Gasses in Magma

More Visous = More Explosive
Viscosity: measure of material's resistence to flow
[higher viscosity->difficult to flow]

Factors Affecting Viscosity
1)TEMPERATURE:
higher temp = less viscous = more fluid (like syrup)
2)COMPOSITION:
-higher silica = more viscous (ryolite)
*more silica means impeded flow bc silica's in chain structures
-lower silica = lower viscosity [more fluid] (eg mafic lava{basalt})
3)DISSOLVED GASSES:
-volatiles (dissolved gas in magma) increase the fluidity of magma (lower viscosity)
-gases expand as magma nears earth's surface due to decreasing pressure
-violence of eruption depends on how easily gases escape from magma
How do Dissolved Gasses affect an eruption: -volatiles (dissolved gas in magma) increase the fluidity of magma

IN addition
-more gas= more force to propel lava...
-before an eruption volatiles (gaseous component of magma) migrate up and accumulate near top of magma chamber
=upper portion of magma is enriched in gases
=gas-charged magma moves from chambe and risses through vent
=as nears surface pressure is reduced
=gases expand
=dissolved gasses release suddenly (like pop can)

*fluid basaltic magmas allow gasses to rise with ease. produce lava fountains. *calm eruptions*

*more viscous magmas = much more explosive.
prior to eruption magmatic differentiation leaves iron-rich minerals behind & upper portion of magma is enriched in silica & dissolved gasses.
when magma in upper portion is released, pressure drops on magma below and explosion is followed by emission of degassed lavas.
*ryolite or andesite*
*yellowstone & mt st helens go BOOM*

------dissolved gasses=1-6% of magma----mostly H20 & Carbon Dioxide
Types of Basaltic Lava Flows: 1) Pahoehoe Flows
-smooth skin that wrinkles
as still molten subsurface continues moving
-twisted ropey texture
-(can make lava tubes)
-hotter, richer in gasses, faster than aa flows

2)Aa Flows
-rough jagged blocky texture
-pahoehoe can turn into Aa
Pyroclastic Material: propelled blobs of lava ejected from volcano ("fire fragments")

Types:
1)Ash & Dust
-fine glassy fragments
2)Pumice
-pourous rock from "frothy" lavas
3)Lapilli
-walnut sized
4)Cinders
-pea sized

*Particles Larger than Lapilli*
5)Blocks
-Hardened/cooled lava
6)Bombs
-ejected as hot lava balls
-~10cm long
Crater (volcano terms): steep walled depression at the summit
-less than 1 km in diameter
-smaller than a caldera
Caldera (volcano terms): very large circular depression at summit
-larger than 1 km in diameter
-its a collapse structure
-produced by a collapse that followed a massive eruption
Vent (volcano terms): the opening of a pipe that connnects to a magma chamber
3 Types of Volcanos: 1) Shield Volcanos
2) Cinder Cones
3) Composite Cones
Shield Volcanos: -broad, dome-shaped
-made up of Basaltic Lava
-covers large area
-produced by mild eruptions of mass amts of lava
-ex. Mauna Loa (hawaii)
-Olympus Mons (on mars = huge shield volcano
-calderas common to mature shield volcanos
-once a shield eruption volcano is well established most of lava flows through lava tubes -> increase the distance lava can travel before it solidifies
Cinder Cone Volcanos: -Built from ejected lava fragments (mainly cinder-sized)===>>made of pyroclastic material
-steep slope
-have large deep craters
-usually product of single eruptive episode
-usually small
-usually occur in groups
Composite Cone Volcanos (Stratovolcano): -potentially dangerous
-most located in "ring of fire" which rims the PACIFIC OCEAN
-large, classic shape (thousands feet high, miles-wide base)
-due to thick lava that travel short distances
-made up of interlayed layers of lava flows and layers of pyroclastic debris
-most violent volcanos
-often produce nueé ardente
[the most destructive form of pyroclastic flow]
-Can produce a LAHAR [a volcanic mudflow]
-ex. Mt St Helens
nueé ardente: -the most destructive pyroclastic flow {flows of a mix of hot gases, ash, & large rock fragments}

-the bottom portion is suspended by jets of buoyant gases passing up through flow
-trapped air provides buoyancy
===travels in nearly frictionless enviro
=====can race down steep volcanic slopes
==go up to 200km/hr

**produced by composite cone volcanos**
Lahar: a mudflow occuring when volcanic debris becomes saturated with water

-can be triggered by ice melting when volcano erupts

**caused by composite cone volcanos**
pyroclastic flows: explosive mix of rock glass & heat
-only with felsic & intermediate magma
-ash, pumice & other fragments propelled at high speed
Crater Lake formed from a Caldera: the magma chamber is partially emptied
-the dome part of volcano collapses
-forms crater :)
The greatest volume of lava is extruded by:: FISSURE ERUPTIONS
fissure eruptions: basaltic lava is extruded from fractures in crust (called FISSURES)
-some can flow far away from source (*flood basalts*) & cover huge areas
-occur worldwide
-ex. Columbia Pateau
----Snake River Plain in
Lava Domes (volcanic landform): bulbous mass of solid lava
-from explosive eruptions of gas rich magma (silica rich)

[late stages andesitic composite cones... looks like bulge inside of top of volcano]
Volcanic Pipes v Necks: PIPES:
-short channels connecting magma chamber to surface

NECKS:
-resistent vents left standing after erosion has removed volcano
(ex devils tower in wyoming)
Dikes Sills Lacolliths are all: intrusive igneous features
Dikes: -a crack that cross cuts rocks
-sheetlike injection
-occurs when magma's injected into fractures
-look like a wall if material around it erodes
-"injection into a fracture"
-**vertical**
Sills: -formed when magma's injected sideways into rock layers
-only form at shallow depths where pressure from rocks on top is low (so they can be lifted so sill can flow inbetween)
-"injection into a bedding plane"
-**horizontal**
Lacollith: -occur when magma's intruded between layers near the surface
-magma generating lacollith more viscous (less fluid) & collects, pushing overhead rocks upward
-lens/mushroom shaped mass
-"arches overhead strata upward"
-similar to sill
Granite is Usually Found in: Continents
Basalt Usually found in: BOTH oceanic and continental settings
Most Volcanos are Located: Within / Near Ocean basins

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