Volcanoes: Formation, Types, and Activity

Summary

Professor Dave's geology series delves into the dynamic world of volcanoes, Earth's powerful geological features. He explains how they form due to mantle melting, often at plate boundaries, and discusses their various types, including cinder cones, composite volcanoes, and shield volcanoes. The video also covers large igneous provinces, seafloor volcanism, and kimberlite pipes. It highlights the potential dangers of volcanic activity, such as explosive eruptions and lava flows, and how volcanologists predict behavior to mitigate risks.

Takeaways

• 🌍 Earth is described as a dynamic place with continental crust plates floating on a plastic-like mantle, influenced by forces like wind, water, and gravity.
• 🌋 Volcanoes are Earth's most dynamic features, present on every continent and responsible for creating over 80% of the Earth's surface.
• 🔍 Volcanologists study volcanoes by measuring emitted gases, ground deformation, and seismic activity to predict behavior and understand processes beneath the crust.
• 🌋 Volcanoes form when the mantle melts, often at divergent plate boundaries, subduction zones, or above mantle plumes, leading to different types of volcanic arcs.
• 🔥 Volcanoes can be explosive, erupting felsic lava, or effusive, erupting mafic lava, depending on their location and the composition of the crust they are on.
• 🏔 There are six main types of volcanoes: cinder cones, composite volcanoes, shield volcanoes, large igneous provinces, seafloor volcanism, and kimberlite pipes.
• 🌀 Cinder cones are small, explosive volcanoes with high gas content, forming from the rapid cooling of ejected lava into ash and cinders.
• 🏰 Composite or stratovolcanoes are tall with steep slopes, formed by alternating layers of lava and tephra, and are prone to explosive eruptions.
• 🛡 Shield volcanoes are large with gentle slopes, formed by the eruption of runny basaltic lava, and are common in Hawaii and other areas of mantle plume activity.
• 🌊 Large igneous provinces are massive deposits of igneous rocks, often associated with mass extinctions, and are thought to be caused by mantle plumes.
• 🌌 Seafloor volcanism occurs along mid-ocean ridges and rifts, influencing ocean chemistry, while kimberlite pipes bring up ultramafic magma from deep within the Earth.

Q & A

What is the primary focus of the geology series described in the script?

The primary focus of the geology series is to explore the dynamic features of Earth, particularly volcanoes, and how they form and behave.

How are volcanoes defined by geologists?

Geologists define a volcano as any location where lava erupts onto the surface, either as a subaqueous eruption on the ocean floor or a sub-aerial eruption on land.

What are the two main types of lava described in the script, and how do they differ?

The two main types of lava are pahoehoe and 'a'a. Pahoehoe is a less viscous, higher temperature lava that erupts from basaltic volcanoes, while 'a'a is a more viscous, blocky lava that tends to avalanche down the volcano.

What is the difference between explosive and effusive volcanoes?

Explosive volcanoes erupt silica-rich felsic lava and have high amounts of dissolved gases, leading to explosive eruptions. Effusive volcanoes erupt mafic lava at higher temperatures with lesser amounts of dissolved gases, resulting in less explosive eruptions.

What are the six main types of volcanoes identified by geologists?

The six main types of volcanoes are cinder cones, composite volcanoes, shield volcanoes, large igneous provinces, seafloor volcanism, and kimberlite pipes.

Why are shield volcanoes considered some of the largest on Earth?

Shield volcanoes are some of the largest on Earth because they are formed by the eruption of runny basaltic lava from small vents and fissures that gradually build up to form a volcanic dome with gentle slopes.

What is a large igneous province and how is it formed?

A large igneous province is a massive deposit of igneous rocks formed by the eruption of millions of cubic kilometers of lava in a short geological time, usually associated with mantle plume activity.

How does seafloor volcanism impact ocean chemistry?

Seafloor volcanism impacts ocean chemistry through hydrothermal circulation along the ridge, which leaches magnesium from seawater, potentially causing different minerals to precipitate from seawater and affecting marine organisms' ability to build shells.

What are kimberlite pipes and what significance do they hold for geologists?

Kimberlite pipes are deep-seated magma conduits that bring up ultramafic magma from deep within the mantle. They are significant for geologists because they can contain diamonds, high-pressure minerals, and xenoliths, providing samples of the lower asthenosphere.

How do volcanologists predict volcanic behavior?

Volcanologists predict volcanic behavior by measuring emitted volcanic gases, ground deformation, and seismic activity to understand the dynamic processes beneath Earth's crust.

Outlines

00:00

🌋 Introduction to Volcanoes

Professor Dave introduces the topic of volcanoes, explaining that they are one of Earth's most dynamic features. Volcanoes are found on every continent, including Antarctica, and are responsible for creating over 80% of the Earth's surface. Volcanologists study these structures by measuring emitted gases, ground deformation, and seismic activity to predict behavior and understand the processes beneath the Earth's crust. The formation of volcanoes is linked to the melting of the mantle, which can occur due to decompression melting or the addition of water. Most active volcanism occurs at divergent plate boundaries, such as mid-ocean ridges, and at subduction zones or above mantle plumes. Volcanoes can form along volcanic arcs in subduction zones or as hot spots above mantle plumes. The paragraph also reviews the types of lava and the differences between explosive and effusive eruptions, setting the stage for a deeper exploration of various volcano types.

05:01

🔥 Types of Volcanoes and Their Formation

This paragraph delves into the six main types of volcanoes identified by geologists: cinder cones, composite volcanoes, shield volcanoes, large igneous provinces, seafloor volcanism, and kimberlite pipes. It discusses the structure and activity of volcanoes, which are essentially piles of ash and lava flows. Volcanoes made of unconsolidated material like ash are weak and prone to collapse, while those primarily of lava flows are more stable. The paragraph explains the two main types of lava: basaltic (less viscous, higher temperature) and andesitic (more viscous, blocky). It also describes the explosive nature of certain volcanoes, which eject tephra and can lead to the formation of pyroclastic flows, a deadly volcanic hazard. The paragraph provides examples of each type of volcano, including scoria cones, which are small and explosive, and composite volcanoes, which are tall with steep slopes and can have explosive eruptions. The famous Mount St. Helens is highlighted as an example of a composite volcano.

10:02

🌍 Large Igneous Provinces and Seafloor Volcanism

The paragraph discusses large igneous provinces, which are massive deposits of igneous rocks formed by the eruption of vast amounts of lava over a short geological period. These provinces, such as flood basalts or traps, are associated with mass extinctions, like the Siberian traps and the Deccan traps. The paragraph also explores the role of mantle plumes in the formation of these provinces, comparing them to lollipops with a bulbous head of hot mantle material supplied by a tail connecting to the core-mantle boundary. The discussion then shifts to seafloor volcanism, which occurs along mid-ocean ridges and rift zones, and its impact on ocean chemistry. The paragraph concludes with a mention of kimberlite pipes, which are deep-seated magma conduits that bring ultramafic magma from deep within the Earth to the surface, often containing diamonds and other high-pressure minerals. The paragraph emphasizes the importance of understanding volcanoes for their scientific, economic, and safety implications.

Keywords

💡Volcanoes

Volcanoes are geological structures where molten rock (lava), volcanic ash, and gases escape from beneath the Earth's surface. In the video, volcanoes are described as one of Earth's most dynamic features, responsible for creating over 80% of the Earth's surface. The video explores how volcanoes form and the various types and behaviors of volcanic eruptions, emphasizing their powerful and awe-inspiring nature.

💡Mantle

The mantle is the layer of the Earth located between the crust and the core, composed of semi-solid rock that flows slowly over time. The video discusses how the Earth's plates float atop the mantle, and it explains how mantle melting (due to decompression or the addition of water) leads to the formation of volcanoes. The mantle is crucial for understanding the movement of tectonic plates and the formation of magma.

💡Subduction Zones

Subduction zones are areas where one tectonic plate is forced beneath another into the mantle, causing intense geological activity such as earthquakes and volcanoes. The video explains that volcanoes often form along these zones, with the release of water from the subducted plate into the mantle causing the formation of volcanic arcs. Subduction zones are a key concept for understanding explosive volcanic eruptions.

💡Mantle Plumes

Mantle plumes are columns of hot, solid material that rise from deep within the mantle to the Earth's surface, often causing volcanic activity away from plate boundaries. The video highlights that mantle plumes are responsible for hotspot volcanoes, such as those forming the Hawaiian Islands, and can lead to large-scale volcanic formations known as Large Igneous Provinces (LIPs).

💡Tephra

Tephra refers to fragments of volcanic rock and ash ejected during an eruption. The video describes how explosive volcanic eruptions emit tephra, which can range from fine ash to large volcanic bombs. These materials are significant because they contribute to the formation of volcanic layers and play a role in the destructiveness of eruptions.

💡Pyroclastic Flow

A pyroclastic flow is a fast-moving current of hot gas and volcanic material that flows down the sides of a volcano during an explosive eruption. The video explains that pyroclastic flows are one of the most dangerous volcanic hazards, moving at speeds up to 700 kilometers per hour and reaching temperatures as high as 1000°C. An example mentioned is the eruption of Mount St. Helens, where pyroclastic flows caused widespread devastation.

💡Cinder Cone

Cinder cones, also known as scoria cones, are small, steep-sided volcanoes formed by explosive eruptions that emit lava fragments called cinders. In the video, it explains how cinder cones form rapidly and have short lifespans due to the high gas content in their eruptions. An example is the Parícutin volcano in Mexico, which grew from a fissure in a farmer's field in 1943.

💡Shield Volcano

Shield volcanoes are large, broad volcanoes with gentle slopes formed by the eruption of low-viscosity basaltic lava. The video describes shield volcanoes as some of the largest volcanic structures on Earth, often associated with mantle plumes. The Hawaiian Islands, particularly Mauna Loa, are classic examples of shield volcanoes, characterized by their massive size and relatively non-explosive eruptions.

💡Explosive Eruptions

Explosive eruptions occur when magma with high gas content and viscosity erupts violently, ejecting ash, lava bombs, and pyroclastic flows. The video contrasts explosive eruptions, typically occurring at subduction zones, with effusive eruptions, which produce flowing lava. Explosive eruptions are dangerous due to their sudden and destructive nature, as seen in stratovolcanoes like Mount St. Helens.

💡Lava

Lava is molten rock that emerges from a volcano during an eruption. The video distinguishes between two types of lava: 'pahoehoe,' which is less viscous and flows smoothly, and 'a'a,' which is more viscous and forms a blocky, rugged surface. Lava is central to the formation of various types of volcanoes, and its composition (felsic or mafic) affects the behavior of eruptions.

Highlights

Volcanoes are present on every continent and are responsible for creating over 80% of Earth's surface, above and below sea level.

Volcanologists predict volcanic behavior by measuring emitted volcanic gases, ground deformation, and seismic activity.

Volcanoes form at divergent plate boundaries, subduction zones, and mantle plumes, with different characteristics depending on the crust type (continental or oceanic).

Volcanoes erupt different types of lava: felsic lava tends to be explosive and found on continental crust, while mafic lava is effusive and found on oceanic crust.

There are six main types of volcanoes: cinder cones, composite volcanoes, shield volcanoes, large igneous provinces, seafloor volcanism, and kimberlite pipes.

Scoria cones, or cinder cones, are small volcanoes with high gas content that form rapidly and are short-lived.

The 1943 eruption of Parícutin in Mexico serves as an example of the rapid growth of a scoria cone, forming a 150-meter volcano in just a week.

Composite volcanoes, or stratovolcanoes, are known for their alternating layers of lava flows and tephra, with explosive eruptions due to high water content in the magma.

Pyroclastic flows, which move at speeds of up to 700 kilometers per hour and reach temperatures of up to 1,000°C, are the deadliest volcanic hazard.

The 1980 eruption of Mount St. Helens was the deadliest volcanic event in U.S. history, with a lateral explosion that devastated a large area.

Shield volcanoes are formed by runny basaltic lava, typically away from plate boundaries, with slopes less than 10 degrees and large diameters.

Large igneous provinces (LIPs) involve massive lava eruptions that occur over a short time span and are often linked to mass extinction events.

The Siberian Traps and Deccan Traps are two well-known LIPs associated with mass extinctions, including the end-Permian and end-Cretaceous events.

Kimberlite pipes are magma conduits that bring up material from deep in the mantle, including diamonds and other high-pressure minerals.

Modern volcanologists use seismometers and satellite measurements to monitor signs of volcanic eruptions, such as gas leaks, ground deformation, and increased seismic activity.

Transcripts

he knows a lot about the science star

Professor Dave explains

throughout this geology series we've

been describing the Earth as a dynamic

place where huge plates of continental

crust float Atop A plastic-like mantle

and the forces of wind water and gravity

create unique sedimentary rocks but now

we're going to explore one of Earth's

most dynamic features of all volcanoes

we've all heard of volcanoes before as

these are fascinating and Powerful

structures making them the subject of

myth and Legend over the Millennia

volcanoes are present on every continent

even Antarctica and they are responsible

for creating over 80 percent of Earth's

surface above and below sea level

geologists Define a volcano as any

location where lava erupts onto the

surface either as a subaqueous eruption

on the ocean floor or a sub-aerial

eruption on land the geologists who

study volcanoes who are called

volcanologists measure emitted volcanic

gases ground deformation and seismic

activity in order to predict volcanic

behavior and understand the dynamic

processes beneath Earth's crust we

talked about how volcanoes form when we

were learning about igneous minerals so

let's start with a quick review

volcanoes form above areas where the

mantle melts either due to decompression

melting or melting from the addition of

water most of the ACT active volcanism

on Earth occurs that divergent plate

boundaries especially mid-ocean ridges

on land volcanism occurs along

subduction zones and above mantle plumes

volcanoes form along a curved line

called a volcanic Arc at subduction

zones which corresponds to the area

where the subducted slab releases its

chemically bound water into the mantle

when the overriding plate is oceanic

crust the chain of volcanoes is called

an island arc and when the overriding

plate is continental crust it is called

a continental Arc volcanoes that form

above mantle plumes are called hot spots

which is the only type of volcano that

can form outside of plate boundaries

finally volcanoes on continental crust

tend to be explosive and erupt felsic

lava while volcanoes on oceanic crust

are effusive erupting mafic lava

having reviewed volcanisms causes let's

Now list the types of volcanoes there

are six main types that geologists have

identified on Earth

Cinder cones composite volcanoes

shield volcanoes large igneous provinces

seafloor volcanism and kimberlite pipes

before we elaborate on each type let's

talk a bit more generally about volcanic

structure and activity volcanoes are

essentially just giant piles of

inter-layered Ash and lava flows that

erupt from the volcano's vent or vents

volcanoes that are primarily made of

unconsolidated material like ash are

very weak and prone to collapse whereas

more solid volcanoes that are mainly

lava flows are more structurally sound

there are two main types of lava POI

which is a less viscous higher

temperature lava that erupts from

basaltic volcanoes and aha which is a

more viscous blocky lava that sort of

avalanches its way down the volcano

collapsing under its own weight in

addition to Lava volcanoes can erupt

solid material generally called tephra

which can range from Ash to large

volcanic bombs which are boulder-sized

pieces of material that solidify in the

air during eruption another important

property of is its explosivity explosive

volcanoes erupt silica-rich felsic lava

and have high amounts of dissolved gases

especially water and effusive volcanoes

erupt mafic lava at higher temperatures

and have lesser amounts of dissolved

gases explosive volcanoes tend to form

along Continental arcs while effusive

volcanoes are most common among

mid-ocean ridges and seamounts where

they sit on oceanic crust now back to

the types of volcanoes scoria cones

sometimes called Cinder cones are the

smallest type of volcano standing

between a dozen and one thousand feet

tall they are notorious for their High

dissolved gas content and quick growing

short-lived nature eruptions are powered

by the pressure of their dissolved gases

which come out of solution during

eruption and get frozen into the newly

formed rock this type of volcanic rock

is said to be vesicular

scoria cone eruptions are spattery and

explosive due to their high gas content

when volcanoes erupt explosively their

ejected lava rapidly cools as it flies

through the air forming tiny particles

of Ash and glassy chunks of rocks called

cinders

they are called Cinders because they

resemble ash from a coal furnace though

explosive in nature scoria cones erupt

basaltic lava the volcano itself which

is mainly made of pieces of cinders

piled up at the angle of repose is more

like a pile of sediment than a Rocky

Mountain and is therefore easily eroded

the formation of the volcano parakuten

nicely illustrates the rapid growth of

Cinder cones on February 20th 1943 a

Mexican farmer named dionisio pulido was

tending to his field when suddenly the

ground began to shake and soon swelled

two meters upward forming a fissure that

spewed sulfury Smoke by Nightfall lava

was shooting from the fissure and a 50

meter tall volcano had formed by morning

rising to 150 meters after a week

the volcano stopped erupting in 1952 but

not until forming a scoria cone 424 feet

tall and spreading lava over 26 square

miles in addition to destroying Polito's

Farm the volcano leveled the two nearest

towns and displaced thousands

composite or stratovolcanoes usually

form at subduction zones especially

Continental arcs when most people

imagine a volcano in their minds they

are probably imagining a stratovolcano

stratovolcanoes can rise as tall as 8

000 feet with steep slopes up to 36

degrees the name strata volcano arises

from its structure which is alternating

layers or strata of lava flows and

tephra with a central vent those

stratovolcanoes can produce lava flows

the lava they extrude usually just piles

up atop the vent forming a giant blob of

viscous magma called a lava Dome once

the lava Dome solidifies it plugs up the

volcano stopping it from releasing its

pressure this in combination with the

high water content of their lava leads

to a tendency for extremely explosive

eruptions strata volcano lava is viscous

for two reasons first it is about 500

Degrees lower in temperature when

compared with an effusive volcano like

Hawaii and second it is rich in silica

when silica is a component of a melt it

polymerizes or forms networks of bots

which makes it increasingly resistant to

flow with increasing silica content when

an explosive eruption occurs the pile of

lava and tephra that is the volcano can

be partially or entirely blasted away

and incorporated into a hot rapidly

moving mass of Ash Rock and gas called a

pyroclastic flow after being blasted

into the air by the eruption the

pyroclastic material begins to fall back

down to Earth where it flows along the

ground and spreads out reaching speeds

of up to 700 kilometers per hour with

temperatures of up to 1000 degrees

Celsius

pyroclastic flows are the deadliest

volcanic Hazard and obliterate anything

in their path one of the most famous

composite volcanoes is Mount St Helens

which erupted on May 18 1980 in the

deadliest volcanic event in American

history instead of blowing its top like

most volcanoes Mount St Helens exploded

from the side which directed The

pyroclastic flow laterally flattening an

area 23 miles wide by 19 miles long

large trees were snapped at the base of

their trunks like Twigs 185 miles of

Highway were destroyed and 57 people

were killed

shield volcanoes are some of the largest

volcanoes on Earth and they commonly

formed by mantle plume activity away

from plate boundaries they almost

exclusively extrude runny basaltic lava

from small Vents and fissures that

gradually build up to form a volcanic

Dome with slopes less than 10 degrees

the diameter of typical shield volcanoes

can range from three to four miles with

Heights up to two thousand feet

the Hawaiian Islands are some of the

best examples of shield volcanoes

Mount Aloha one of the Earth's most

active volcanoes is the largest spanning

74 miles from north to south and rising

over 28 000 feet above the ocean floor

large igneous provinces are massive

deposits of igneous rocks where in some

cases millions of cubic kilometers of

lava have been erupted in a very short

amount of time geologically speaking

with the bulk of the magmatism occurring

in less than one million years in most

cases

one type of lip called flood basalts or

traps are large igneous plateaus with a

step-like morphology and are associated

with many of Earth's worst mass

extinctions for example the Siberian

traps which we discussed in the tutorial

regarding Earth's history are often

cited as being the triggering event of

the end Permian mass extinction which

was the worst mass extinction of all

time

in addition another flood Basalt called

the Deccan traps began erupting around

the time of the end Cretaceous

Extinction event which is typically

attributed to an asteroid impact can

this be a coincidence or perhaps the

asteroid impact somehow triggered this

eruption this is a hotly debated topic

among geologists

lips can form over both Oceanic and

continental crust and do not correlate

with tectonic environments so what

causes them due to the extremely high

heat flow required to produce so much

magma over such a short period of time

it has recently been accepted that

mantle plumes are the culprit mantle

plumes sort of resemble lollipops and

have a bulbous head of swirling hot

mantle that is supplied by a smaller

tail which connects down to the core

mantle boundary so as the head of a

plume reaches the crust it causes a

short period of intense volcanism that

tapers off as its tail nears the surface

the Columbia River Basalt is a

well-studied flood Basalt that began

erupting around 17 million years ago in

Southeastern Oregon it is composed of

over 300 individual lava flows with

around 10 000 years between major

eruptions the onset of volcanism was

sudden and intense with 85 percent of

the lava erupting over a 1 million year

period between 15 and 16 million years

ago which slowly tapered off to widely

spaced and sporadic eruptions by 13

million years ago eruption of this lip

was probably related to the Yellowstone

hotspot which was located beneath

Southeastern Oregon during the onset of

volcanism though this too is a highly

debated topic

seafloor volcanism occurs along

mid-ocean ridges where basaltic lava

erupts from large linear volcanoes or

fissures Fisher volcanoes also occur

along areas that are rifting such as

Iceland and East Africa the vast

majority of the lava that is erupted on

Earth over its history has come from

Fisher volcanoes along mid-ocean ridges

the intensity of seafloor volcanism also

has a large impact on Ocean chemistry

due to hydrothermal circulation along

the ridge leaching magnesium from

seawater during times of Rapid sea floor

spreading so much magnesium is removed

from the ocean that different minerals

begin to precipitate from seawater which

even affects the ability of marine

organisms to build their shells

most of the material erupted from

volcanoes comes from the upper mantle

and lower crust but there are cases

where deeper material can get dragged to

the surface during an eruption Kimber

light pipes are deep-seated magma

conduits or pipes that draw up

ultramafic magma from 150 to 450

kilometers below the surface and exhibit

violent explosive eruptions that rapidly

carry mantle material to the surface

Kimber lights often contain diamonds and

other high pressure minerals like COA

site a polymorph of quartz they also

have an unusual chemistry for ultramafic

rocks being rich in potassium sodium

phosphorus and carbon in addition Kimber

lights can contain fragments of rock and

large crystals called xenoliths that

provide geologists with their only

physical samples of the lower

asthenosphere the most recent kimberlite

eruption occurred ten thousand years ago

in Tanzania

so that covers the types of volcanoes

and their formation while volcanoes are

fascinating and awe-inspiring they can

also be extremely deadly and dangerous

sulfuric gas emissions razor-sharp

tephra lung filling Ash molten lava

pyroclastic flows and fast-moving mud

flows of volcanic ash called lahars

cause widespread health effects and

property destruction however with new

developments in seismometers and

satellite measurements of ground

deformation volcanologists can monitor

the telltale signs of volcanic eruptions

some of the most important signs of a

volcanic eruption are gas leaks

deformation or bulging around the

volcano increased seismic activity and

phreatic eruptions where steam is

released from volcanic vents of course

most of us do not live near active

volcanoes but many people do and these

structures remain an important focus of

geological research

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