Violent Volcanoes- Kaboom!

What did Mummy Volcano say to Baby Volcano?

- I lava you!

Volcanoes (origins…)

So, who on Earth came up with the name volcano to describe a smouldering mountain that can explode? Well, there are different stories around the world to explain what causes volcanoes, but you can blame the actual name on the ancient Romans and their hot-tempered fire god, Vulcan…

According to legend, Vulcan lived on the island of Vulcano, inside a smouldering mountain.

Volcanoes (origins…)

All the smouldering, sparks and rumbling noises were caused by Vulcan’s frantic activities. He was blacksmith to the gods… He made weapons for Mars…

Armour for Hercules…

Volcanoes (origins…)

And thunderbolts and lightning for Jupiter.

But Vulcan used his skills in other ways too. For no good reason, Vulcan would pick on villagers and terrorise them with fire, lightning, lava flows and explosions!

So, which came first, Vulcan or Vulcano? No one knows, but the name, tweaked a bit, stuck.

Volcanology (a proper definition)

• Includes all processes by which solid, liquid or gaseous materials are forced into the Earth’s crust or are ejected onto the surface

Lesson Objectives

• Main features of a volcano– Physical characteristics– Internal forces

• Processes that create volcanoes• Life of volcanoes

Main Features of a Volcano – Physical Characteristics

• Vent: An opening in the Earth’s surface

• Pipe: A channel which allows the magma to rise to the top of the volcano during an eruption

• Crater: A bowled-shaped opening at the top of the volcano

• Cone: The shape of the volcano

Main Features of a Volcano – Internal Forces

• When the temperature beneath the Earth’s surface is so great, magma (molten mantle) is formed

• Magma that reaches the Earth’s surface is called lava• Vulcanicity is the process in which magma and other

materials reach the Earth’s surface

• Volcanoes grow by intrusion and extrusion- An intrusion is magma that moves up into a volcano and then it stops,

never erupting volcano grows on the inside- An extrusion is an eruption can add layers of lava or ash volcano

grows on the outside The outpouring of the lava onto the Earth’s surface is called an eruption.

• Hardened lava from eruptions through a single hole or vent may result in a cone-shaped mountain called a volcano

Main Features of a Volcano – Internal Forces

Processes that Create Volcanoes• Convergent plates

– Mantle above subducting plate, below over-riding plate hot but not hot enough to melt rock

– Oceanic plate on the ocean floor for tens of millions of years, incorporating a lot of water and buried in sediment

– As plate subducts, comes into contact with overlying hot mantle

– Causes water and sediment to melt and move into overlying mantle

– Lowers melting temperature of mantle enough to generate magma

• Divergent plates– Accumulation of lava at the

surface – Magma mostly originates by

melting in the mantle– As hot rock gets closer to the

surface the pressure decreases and the rock begins to melt magma.

– Magma more buoyant than the surrounding rock rises towards surface and may supply a volcano (or solidify before it reaches the surface)

Processes that Create Volcanoes

• Hotspots– Source of heat and/or magma

supplied to surface– BUT exact nature of hotspots

poorly known– Stationary with respect to the

moving lithosphere – Linear chains of volcanoes form

on the overlying plates – Volcanoes get older as you look

in the direction of plate motion

Example of Volcanic Hotspots:The Hawaiian Islands

Example of Volcanic Hotspots:The Hawaiian Islands

• This movement takes it to the northwest compared to the layers below it at a rate of 5 to 10 cm/yr

• As the plate moves over a fixed spot deeper in the Earth where magma (molten lava) forms, a new volcano can punch through this plate and create an island

• As the plate moves away, the volcano stops erupting and a new one is formed in its place

• With time, the volcanoes keep drifting westward and getting older relative to the one active volcano that is over the hot spot

• As they age, the crust upon which they sit cools and subsides + erosion of the islands once active volcanism stops shrinking of the islands with age eventual submergence below the ocean surface

Life of Volcanoes

• Active• Dormant• Extinct

• Active– A volcano that has shown eruptive activity

within recorded history– Need not be in eruption to be considered active– 600 volcanoes on Earth considered to be active– 50 to 60 of volcanoes actually erupt yearly

Life of Volcanoes

• Extinct– A volcano that has not shown any historic activity– Usually deeply eroded, and shows no signs of

recent activity  – How old a volcano must be to be considered

extinct depends to a large degree on past activity.• Yellowstone Caldera: about 600,000 years old and is

deeply eroded, but geothermal activity, hot springs, and geysers all point to the fact that magma still exists beneath the surface not considered extinct 

• Other volcanoes that are deeply eroded, smaller, and much younger than Yellowstone, that show no hydrothermal activity may be considered extinct

Life of Volcanoes

• Dormant (aka sleeping volcano)– Somewhere between active and extinct– Has not shown eruptive activity within recorded history

but shows geologic evidence of activity within the geologic recent past

– Because the lifetime of a volcano may be on the order of a million years, dormant volcanoes can become active volcanoes all of sudden   perhaps the most dangerous

– Examples:• Yellowstone Caldera would be considered a dormant volcano.• Mount St. Helens was a considered a dormant volcano, having

not erupted for 123 years, before its reawakening in 1980.  • Mount Pinatubo in the Philippines had been dormant for over

400 years before its eruption in 1991.• Mount Vesuvius, near Naples, Italy was considered an extinct

volcano prior to its devastating eruption of 79 A.D.

Life of Volcanoes

• Dormant (aka sleeping volcano)– Examples:

• Yellowstone Caldera would be considered a dormant volcano.

• Mount St. Helens was a considered a dormant volcano, having not erupted for 123 years, before its reawakening in 1980. 

• Mount Pinatubo in the Philippines had been dormant for over 400 years before its eruption in 1991.

• Mount Vesuvius, near Naples, Italy was considered an extinct volcano prior to its devastating eruption of 79 A.D.

Life of Volcanoes