Geology Exam 1 2
Terms
undefined, object
copy deck
- 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