volcanism

Volcano

a hill or mountain that forms around a vent where lava, pyroclastic materials, and gases erupt, so it is a landform-a feature on Earth’s surface.

Volcanism refers to

all processes related to the rise and discharge of magma and gases at the surface or into the atmosphere.

The term Volcanism refers to all processes related to the rise and discharge of magma and gases at the surface or into the atmosphere.

Thus, volcanism accounts for

the origin of all volcanic (extrusive igneous) rocks, such as basalt, tuff, and obsidian; as well as features like volcanoes, fissures, and basalt plateaus

Several gases are emitted, but in most cases you’ll find ___________being the most common,

water vapor

Several gases are emitted, but in most cases you’ll find water vapor being the most common, followed by_______,and others in minor quantities.

carbon dioxide, sulfur dioxide

Physical Characteristics of Lava

Violence of eruptions controlled by:

Amount of volatiles-

●more dissolved gases in the magma the more volatile

○Ease or difficulty of gases escaping to atmosphere

Physical Characteristics of Lava

Viscosity –

●a fluid’s resistance to flow

○Higher silica contents produce higher viscosity.

○Lower silica content produces lower viscosity

Physical Characteristics of Lava

●Temperature of the lava

○Cooler lavas have higher viscosity.

○Hotter lavas have lower viscosity

Lava flows rarely cause fatalities, they flows rather slowly and flow in low areas. Lava can begin to move more rapidly when their margins cool to form a channel, and especially when insulated on all sides in a

lava tube

lava tube-

forms within a flow when its margins and upper surface solidify, thereby forming a conduit through which lawva can move rapidly and for great distances.

Lava Flows

Geologists in Hawaii characterize (low viscosity) basalt flows as

pahoehoe or aa.

Lava Flows

Pahoehoe

has a smooth ropy surface much like taffy

Lava Flows

Aa

flow consists of rough, jagged, angular blocks and fragments

Lava Flows

Much of the igneous rock in the upper oceanic crust is a distinctive type made up of bulbous masses of basalt that resemble pillows, named

pillow lava.

Lava Flows

pillow lava forms when

lava is rapidly chilled underwater

Lava Flows

Mafic lava flows (sometimes intermediate flows) show a pattern of columns bounded by fractures, called

columnar jointing

Lava Flows

For columnar joints to form, the lava flow must cease moving, and cool and contract, setting up for the fractures known as___to open

joint

Lava Flows

These fractures are commonly__________(six-sided) that extend downward, outlining the columns with their long axes perpendicular to the cooling surface

polygonal

Pyroclastic Materials

In addition to lava flows, erupting volcanoes eject pyroclastic materials, especially________a designation for pyroclastic particles that measure less than 2.0mm.

volcanic ash

Pyroclastic Materials

This ash will fall from the shy due to gravity called__________for when it flows along/close to the land surface.

ashfall and ashflow

Pyroclastic Materials

In addition to ash, volcanoes erupt

lapilli

●pyroclastic material measuring 2-64mm

Pyroclastic Materials

In addition to ash, volcanoes erupt

blocks/bombs-

●measuring greater than 64mm

Pyroclastic Materials

In addition to ash, volcanoes erupt

Bombs-

○twisted, streamlined shape, indicating that they were erupted as globs of magma that cooled and solidified during their flight through the air.

Pyroclastic Materials

In addition to ash, volcanoes erupt

Blocks-

in contrast, are angular pieces of rock ripped from a volcanic conduit or pieces of a solidified crust of a lava flow

Types of Volcanoes

Although volcanoes vary in size and shape, all have a________leading to a magma chamber beneath the surface.

conduit(s)

Types of Volcanoes

Most volcanoes have a circular depression known as a_______at their summit, that forms by explosions or collapse

crater

Types of Volcanoes

caldera

a huge structure that forms following voluminous eruptions during which part of the magma chamber drains and the mountains summit collapses into the vacated space below.

Types of Volcanoes

Most volcanoes have a circular depression known as a crater at their summit, that forms by explosions or collapse. A caldera is a huge structure that forms following voluminous eruptions during which part of the magma chamber drains and the mountains summit collapses into the vacated space below.

An excellent example is misnamed

Crater Lake in Oregon

Types of Volcanoes

Crater Lake is actually a

steep-rimmed caldera that formed about 7,700 years ago in the manner just described; it is more that 1,200 m deep and measure 97, by 6.5 km.

As impressive as it is, it is not nearly as large as other calderas on Earth.

Types of Volcanoes-

Volcanoes that look much like the outer surface of a shield laying on the ground with the convex side up are called

Shield Volcanoes

Shield Volcanoes

●Composed almost entirely of low-viscosity mafic lava flows so the flow spreads out and thin

●These volcanoes are rather quiet type of eruptions in comparison to other volcanoes

●Most common in ocean basins, but some present on continents

●Common in CA, OR,HI islands=5 huge shield volcanoes and East Africa

Types of Volcanoes-

Small, steep-sided _______s made up of particles resembling cinders from when pyroclastic materials accumulate around a vent from which they erupted.

Cinder Cone

This is describing a Cinder Cone Volcanoes

Cinder Cone Volcanoes

●Rarely exceeding 400 m high, with slope angles up to 33 degrees

●Most are perfectly symmetrical unless prevailing winds cause the pyroclastic material to build up higher on the downwind side of the vent.

●Common in Rocky Mountain states, particularly New Mexico and Arizona, as well as CA, OR, WA, HI

Types of Volcanoes-

Composite Volcanoes

Also known as Stratovolcanoes have pyroclastic, as well as intermediate lava flow layers. As the lava flows cool, they typically form andesite, recall that intermediate lava flows are more viscous than mafic ones.

Types of Volcanoes-

Composite Volcanoes

Geologists use the term lahar for volcanic mudflows;

a lahar may form when rains falls on unconsolidated pyroclastic materials and creates a muddy slurry that moves downslope.

Types of Volcanoes-

Composite Volcanoes

●These volcanoes are steep-sided, conical mountains and the angle of their slope decreases towards the base.

●Most common at convergent plate boundaries

Ex:

: Mount Shasta in CA

are less common than all of the volcanoes previously discussed.

Lava domes

Lava domes

steep-sided, bulbous mountains that form when viscous felsic magma, and occasionally intermediate magma, is forced toward the surface. Because felsic magma is so viscous, it moves upward very slowly and only when the pressure from below is great.

●Lava dome eruptions are

some of the most violent and destructive.

Lava Domes

ex:

: In 1902, Mount Pelee on the island of Martinique had a tremendous explosion, ejecting a mobile dense cloud of pyroclastic materials and a glowing cloud of gases and dust called a nuee ardente (French for “glowing light”) This cloud of gases had a temperature of 700℃ and incinerated everything in its path. It only took 2-3 minutes to travel to the nearest city of St. Pierre and killed nearly 28,000 residents

Geologists have no formal definition for _________ eruptions, but we can take it to mean and explosive eruption of hundreds of cubic kilometers of pyroclastic materials and the origin of a huge caldera

supervolcano

No supervolcano eruptions have occurred in historic times,

but geologists know of several that took place during the past 2 million years.

No supervolcano eruptions have occurred in historic times, but geologists know of several that took place during the past 2 million years.

For example:

we can summarize Yellowstone’s volcanic history by noting that eruptions took place 2 mya, 1.3 mya, and 600,00 years ago.

Geologists think that these huge eruptions were caused by a rising

mantle plume,

Geologists think that these huge eruptions were caused by a rising mantle plume,

a cylindrical mass of magma probably rhyolitic in composition, Because this type of magma is viscous, it triggers explosive eruptions when its near the surface.

Other Volcanic Landforms

Basalt Plateau-

Lava flows build up a plateau shaped landform made of basalt. Result of a very large volume eruption of basalt lava.

Other Volcanic Landforms

Fissure Eruption-

Rather than erupting from central vents, lava flows from long cracks in Earth’s crust as a linear volcanic vent.

Other Volcanic Landforms

Pyroclastic sheet deposits-

Extensive, relatively flat-lying accumulations of pyroclastic material.. These result from numerous eruption of very large volumes of extremely fluid, basaltic lavas, which accumulate as sheet-like flows covering large areas.

Volcano Belts

Most of the world’s active volcanoes are in well-defined zones or belts rather than randomly distributed. The ___________ popularly called the Ring of Fire, has more than 60% of all active volcanoes.

circum-Pacific belt,

Volcano Belts

The second area of active volcanism is the__________,k about 20% of all active volcanism takes place in this belt

Mediterranean belt

Volcano Belts

Nearly all the remaining active volcanoes are at or near

Nearly all the remaining active volcanoes are at or near

Plate Tectonics, Volcanoes, and Plutons

Reminder:

Mafic magma is generated beneath spreading ridges at a

1.divergent boundary, creating oceanic crust

Plate Tectonics, Volcanoes, and Plutons

Reminder:

Intermediate or felsic magma forms where an oceanic plate is

1.subducted beneath another oceanic/continental plate at a convergent boundary

Igneous Activity at a Divergent Boundary

Mafic lava is very fluid, allowing gases to escape easily, and at great depth in the oceans

the water pressure is so great that explosive volcanism is prevented.

Igneous Activity at a Divergent Boundary

Mafic lava is very fluid, allowing gases to escape easily, and at great depth in the oceans, the water pressure is so great that explosive volcanism is prevented.

●No pyroclastic material

●Effusive eruptions of basaltic magmas and pillow lavas.

●Formation of most of the sea floor.

●Ex: Mid-Atlantic ridge

Igneous Activity at a Convergent Boundary

●Most large well–known volcanoes, located in the

circum-Pacific Belt

Igneous Activity at a Convergent Boundary

●Explosive composite volcanoes, pyroclastic debris

●The convergence leading to subduction causes a chain of continental volcanoes called a volcanic arc

●Viscous andesitic or felsic lavas.

Intraplate Volcanism

●Interior of a plate, neither a convergent or divergent boundary

●Mantle Plumes (Hot Spots) – Ex: Hawaii, Yellowstone.

Hawaiian islands begin as a submarine volcano until

●they protrude out of the water, creating a volcanic island.

●Mantle Plumes (Hot Spots) – Ex

Hawaii, Yellowstone.

Intraplate Volcanism

●Basaltic magma/lava.

●Kauai formed about 5.6-3.8mya, whereas Hawaii began forming less than 1mya

Volcanic Hazards, Monitoring/Predicting Eruptions

Living near a volcano does pose some risk

●Lava flows with few exceptions pose little threat to humans but can destroy property

●Nuee ardentes and volcanic gases are threats during an eruption

●Lahars and landslides may take place even with no eruption

Volcanic Hazards, Monitoring/Predicting Eruptions

The most widely used indication of the size of a volcanic eruption is the Volcanic Explosivity Index (VEI), it ranges from 0 (gentle) to 8 (cataclysmic) and is based on several aspects of an eruption, such as:

●The volume of material explosively ejected

●The height of the eruption plume

This index does not consider the volume of lava, fatalities, and property damage.

Volcanic Hazards, Monitoring/Predicting Eruptions

Is it possible to forecast eruptions?

Volcano monitoring involves recording and analyzing physical and chemical changes at volcanoes.

Geologists monitor things like:

●Gas emissions

●Groundwater level change

●Temperature

●Hot spring activity

●Local magnetic and electrical fields

●Volcano slope changes, from inflating as magma rises

●Paleo Volcanoes- past eruptions

Volcanic Hazards, Monitoring/Predicting Eruptions

The most important: the detection of a volcanic tremor- continuous ground motion that lasts for minutes to hours

○This is different than an earthquake that usually are sudden, sharp jolts.

○Volcanic tremors,also known as harmonic tremors, indicate that magma is moving beneath the surface

Volcanic Hazards, Monitoring/Predicting Eruptions

Is it possible to forecast eruptions?

Monitoring volcanoes can help predict future eruptions, geologist have successfully gave timely warnings to many impending eruptions.

While some eruptions can be easier to predict than others; geologist have even issued low-level warnings where nothing happened but we can prepare ourselves as best as we can for when volcanoes do erupt.

Monitoring Volcanoes

Volcano status – Approximately ______potentially active volcanoes worldwide

1,500 

Monitoring Volcanoes

Active

●if currently or recently eruptive (Approximately 500 in the world today).

Monitoring Volcanoes

Dormant

if it hasn’t erupted in many thousands of years but is expected to erupt in the future

Monitoring Volcanoes

Extinct

haven’t erupted in many years and show no signs of any future eruptions

Importance of Volcanoes- Why We Care

mosphere was originally created from gases released from

●volcanic eruption.

Importance of Volcanoes- Why We Care

was produced by condensation of volcanic water vapor.

Hydrosphere

Importance of Volcanoes- Why We Care

●Lava flows and ash weather to produce fertile soils.

●Violent eruptions can destroy nearly all life in their paths so it is important to monitor them.

●Large amounts of ash and volcanic gases in atmosphere can trigger rapid climate changes and contribute to mass extinctions (which they already have).

Volcanoes

• The surface feature we see on earth 

• Where eruption comes from 

• Gasses and magnum reaching the surface

Volcanism

The origin of all volcanic igneous rock and the volcano’s fissures and basalt plateaus

Volcanic gases

Gases admitted during erruptin

Volcanic gases

Mostly

water vapor (H2O in vapor form)

Volcanic gases

Second most common

 carbon dioxides

Volcanic gases

Third

• : surfer dioxide

Volcanic gases

the rest

A few other minor quantity gasses

Decompression melting

• As molten rock makes its way to the surface, the decompression from going deep in the earth to the surface allows the rocks to melt more and creates more magma.

• As the pressure is reduced the gas begins to expand 

• The gases affect how viscous the magma will be

Volcanic gases

As gas increases, the eruptions become

more volatile, more explosive/ eruptive

Volcanic gases

• Effusive eruptions, meaning opposite of explosive , happens when gas has a hard time escaping 

• Most volcanic acids cause little threat to humans, and dissipate fast into the atmosphere

• CO2 has climatic effects, its a greenhouse gas

Physical characteristics of lava

• How easily gasses can escape determines explosive or effusive

• Viscosity is fluid’s resistance to flow 

• Low viscosity= easy flow 

• Things of higher silica content have a higher viscosity

• Anything felsic is going to have majority silica 

Physical characteristics of lava

Low silica (ex: magma) have lower velocity

This is the malefic category of rock

Cooler lavas have a

higher viscosity (solid isn’t going to flow as easily as something heated and runny)

Lava flows

• Rarely cause death

• Flow to lowlying ares under the influence of gravity 

• It can more rapidly if it channelizes itself

Lava tubes

• Conduits  underground that allows lava to centralize and floor a greater distance

Salt flows

Mafic, low viscosity, easy flow

Salt flows

Pohoehoe flow

Smooth ropey texture

Salt flows

Aa flow

angular , blocky, fragmented pieces

Oceanic crust

• Made of basalts

• Mafic

Oceanic crust

When they solidify quickly the form masses, clumps of lava, called ____

• Its when lava rapidly cools underwater

• pillow lava

Lava flows

Lava comes to a resting position, cools,, then contracts and fractures

• Forms joint (fractures without joints)

• They cool form the top and work their way

Pyroclastic materials

•  pyro meaning fragments

• Clastic meaning fire

• Fire fragments

Pyroclastic materials

• Fire fragments

• Something else that gets exuded from volcanoes  

• Ash

Pyroclastic materials

Ash

• Small microscopic shards of rock

• Tiny shards of glass that can be harmful when inhaled

Pyroclastic materials

Ash & Finely round matter

Types of volcanoes

• All have a conduit (up to the surface connector that leads magma out)

• The very top is the crater

• Formed by the exposition

• After eruption, the volcano can collapse, creating a caldera

Types of volcanoes

Caldera

Large structure formed when the voluminous eruption during which the magma chamber has been drained, then the crater collapse into itself

Types of volcanoes

Caldera

After crater lake erupted and formed the caldera

•  it started forming a new volcano, wizard island