Volcanoes & Volcanic Landforms Mini Quiz To Begin Volcanoes 1. What is the difference between magma and lava ? 2. What kind (type) of rocks are formed

Volcanoes & Volcanic Volcanoes & Volcanic LandformsLandforms

Mini Quiz To Begin Mini Quiz To Begin VolcanoesVolcanoes

1. What is the difference between 1. What is the difference between magma and lava ? magma and lava ?

2. What kind (type) of rocks are 2. What kind (type) of rocks are formed from the cooling of this formed from the cooling of this magma or lava? magma or lava?

3. Why does magma force its way up 3. Why does magma force its way up to the surface of the earth ? (hint: to the surface of the earth ? (hint: what does it want to do?) what does it want to do?)

Volcano BackgroundVolcano Background

Volcano…Volcano… a term borrowed from the a term borrowed from the Romans… Vulcan was the Roman Romans… Vulcan was the Roman God of fire that forged metal… the God of fire that forged metal… the vent (or chimney) of his furnace was vent (or chimney) of his furnace was an island named Volcano… this was an island named Volcano… this was a simple attempt by people to try to a simple attempt by people to try to understand the complex processes understand the complex processes that cause volcanic activitythat cause volcanic activity

Volcano: A DefinitionVolcano: A Definition

Volcano is the modern term used Volcano is the modern term used to describe vents in the earth’s to describe vents in the earth’s surface through which molten rock, surface through which molten rock, heated rock debris, gases and heated rock debris, gases and water vapor are expelled from water vapor are expelled from beneath the earth’s surface in beneath the earth’s surface in igneous processesigneous processes

Volcanic MaterialsVolcanic Materials

The stuff that results from volcanic The stuff that results from volcanic activity can be in the form of solids, activity can be in the form of solids, liquids and gases… some of these liquids and gases… some of these materials includematerials include

water vapor (the major gas water vapor (the major gas expelled)expelled)

rock (lava or magma)rock (lava or magma) pyroclastic materialspyroclastic materials

Pyroclastic MaterialPyroclastic Material

Anything that is ejected from a Anything that is ejected from a volcano is termed Pyroclastic...volcano is termed Pyroclastic...

PyroPyro = fire & = fire & ClasticClastic = particles = particles Pyroclastic materials that are Pyroclastic materials that are

ejected and go airborne are ejected and go airborne are termed termed Tephra Tephra

TephraTephra

Classified according to size:Classified according to size:– ASHASH : less than two millimeters in size : less than two millimeters in size– LAPILLILAPILLI : 2 mm to 64 mm in size : 2 mm to 64 mm in size– BLOCKSBLOCKS : >64mm ejected as solid : >64mm ejected as solid– BOMBSBOMBS : >64mm ejected as liquid : >64mm ejected as liquid

TephraTephra

Although pyroclastic materials are Although pyroclastic materials are born of fire (igneous), as they fall to born of fire (igneous), as they fall to the ground and settle they become the ground and settle they become sedimentary!sedimentary!

Igneous RocksIgneous Rocks

Igneous rocks fall into two Igneous rocks fall into two categories:categories:

Intrusive (plutonic) that cool slowlyIntrusive (plutonic) that cool slowly

and and

Extrusive (volcanic) that cool Extrusive (volcanic) that cool quickerquicker

Magma CompositionsMagma Compositions

There are three general types of There are three general types of volcanic magma compositions :volcanic magma compositions :

– Basaltic Basaltic – AndesiticAndesitic– RhyoliticRhyolitic


These magmatic compositions are These magmatic compositions are classified according to the amount classified according to the amount of silica present…of silica present…

the less silica present, the more the less silica present, the more fluid the magma/lava will befluid the magma/lava will be

the more silica present, the more the more silica present, the more viscous the magma/lava will beviscous the magma/lava will be


Magma compositions classified by Magma compositions classified by the percent silica present turn out the percent silica present turn out like this:like this:

– basaltic : 50 % silicabasaltic : 50 % silica– andesitic : 60 % silicaandesitic : 60 % silica– rhyolitic : 70 % silicarhyolitic : 70 % silica

Explositivity of MagmasExplositivity of Magmas

The more silica that is present, the more The more silica that is present, the more viscous (stickier) that magma is…viscous (stickier) that magma is…

Basaltic : 50% Si, fluid, not explosiveBasaltic : 50% Si, fluid, not explosive Andesitic : 60% Si, “regular” explosionsAndesitic : 60% Si, “regular” explosions Rhyolitic : 70% Si, really big bangs !Rhyolitic : 70% Si, really big bangs !

Land Shapes via Magma Land Shapes via Magma TypeType

The magmatic composition not only The magmatic composition not only controls the color and explositivity, controls the color and explositivity, but it also controls the external but it also controls the external volcanic land features… those volcanic land features… those magmas that are fluid when they magmas that are fluid when they erupt tend to run like molasses while erupt tend to run like molasses while the really sticky magmas don’t really the really sticky magmas don’t really erupt at all… they just blow up.erupt at all… they just blow up.


Basaltic : 50% Si , fluid.Basaltic : 50% Si , fluid. Basaltic eruptions tend to flow out Basaltic eruptions tend to flow out

on the earth’s surface like on the earth’s surface like molasses… initially it will mound up molasses… initially it will mound up but will settle out under the but will settle out under the influence of gravity forming a broad, influence of gravity forming a broad, low shield-like volcano called…. low shield-like volcano called….

You guessed it - a shield volcanoYou guessed it - a shield volcano


Andesitic : 60% Si, kind of viscousAndesitic : 60% Si, kind of viscous Andesitic eruptions are what most Andesitic eruptions are what most

people typically associate with people typically associate with volcanic eruptions… there are lava volcanic eruptions… there are lava flows, ash clouds, and nuee flows, ash clouds, and nuee ardentes. Andesitic eruptions can ardentes. Andesitic eruptions can form two volcanic landforms… form two volcanic landforms…

composite cones and cinder conescomposite cones and cinder cones


Composite volcanoes are volcanoes Composite volcanoes are volcanoes built of alternating flows of lava and built of alternating flows of lava and pyroclastic material… composite pyroclastic material… composite cones are larger than cinder cones cones are larger than cinder cones but aren’t as steep… the composition but aren’t as steep… the composition of these volcanoes is mainly of these volcanoes is mainly andesitic… most large active andesitic… most large active volcanoes around the world are volcanoes around the world are composite volcanoes…composite volcanoes…


Cinder cones are volcanoes that Cinder cones are volcanoes that have steep slopes (~30 degrees) have steep slopes (~30 degrees) and a large crater at the top… and a large crater at the top… these volcanoes are composed these volcanoes are composed entirely of fragments of volcanic entirely of fragments of volcanic rock and material… these rock and material… these fragments are generally basaltic or fragments are generally basaltic or andesitic in composition…andesitic in composition…


Rhyolitic : 70% Si, very viscous!Rhyolitic : 70% Si, very viscous! Rhyolitic eruptions generally don’t Rhyolitic eruptions generally don’t

produce any distinctive landform at produce any distinctive landform at all… the stuff is so viscous (sticky) all… the stuff is so viscous (sticky) that it pressurizes until it just blows that it pressurizes until it just blows up creating a big hole in the ground… up creating a big hole in the ground… all that remains are usually basins all that remains are usually basins that are hotbeds of volcanic activity that are hotbeds of volcanic activity

So, where are these So, where are these landforms?landforms?

The low-slung broad landforms The low-slung broad landforms that characterize basaltic shield that characterize basaltic shield volcanoes are nicely demonstrated volcanoes are nicely demonstrated by some well-known island chains:by some well-known island chains:

Hawaiian IslandsHawaiian Islands Galapagos IslandsGalapagos Islands


The steep sloped sides of the The steep sloped sides of the cinder cone volcanoes can be cinder cone volcanoes can be found throughout Central and found throughout Central and South America and many other South America and many other places world-wide… just take, for places world-wide… just take, for example, Paracutin in Mexico...example, Paracutin in Mexico...


The classic volcano shape that we The classic volcano shape that we all think of is demonstrated well by all think of is demonstrated well by Mt Ranier in Washington State, or Mt Ranier in Washington State, or the most photographed volcano in the most photographed volcano in the world… Mt Fuji in Japanthe world… Mt Fuji in Japan


Rhyolitic landforms are noted by Rhyolitic landforms are noted by their absence… there is usually their absence… there is usually nothing left after a rhyolitic nothing left after a rhyolitic eruption but a hole in the ground eruption but a hole in the ground that is active with geothermal that is active with geothermal energy…just like Iceland or energy…just like Iceland or Yellowstone National Park...Yellowstone National Park...

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Volcanoes & Volcanic Landforms Mini Quiz To Begin Volcanoes 1. What is the difference between magma and lava ? 2. What kind (type) of rocks are formed