1. Volcanoes
Chapter 9
Lesson 2

2. Videos
Volcanoes 101 National Geographic.
Ten things you didn’t know about volcanoes
60 minutes story Jan. 2014
Raging Planet – Volcanoes
Bill Nye – Volcanoes

3. What is a volcano?
A volcano is an opening in Earth's crust through which hot molten rock, rock fragments, and hot gases erupt.

4. Types of Volcanoes
Some volcanoes are large mountains with summits, or peaks, reaching 20,000 feet or more above sea level.
Others are small domes of ash or lava that on average are only about 100 feet high.
Scientists recognize six main types of volcanoes:
Fissure volcano Shield volcano
Cinder Cone volcano 5. Dome volcano
Composite or Stratovolcano 6. Caldera volcano

5. Fissure Volcano
A fissure volcano is a crack in the Earth’s crust. It measures many miles long.
Magma erupts through the fissure and flows down the sides of the volcano in little rivers, to form a gentle slope on each side.

6. The fissure vent eruption on Eyjafjallajokull in Iceland on March 21, 2010.

7. Cinder Cone Volcano
A cinder cone is a steep, cone-shaped hill formed by the eruption of cinders and other rock fragments, which pile up around a single crater.
Cinders form as gas-rich magma erupts, and small chunks harden before they hit the ground.
Many cinder cones form on the sides of other types of volcanoes.
Sunset Crater in Arizona

8. Paricutin in Mexico

9. Composite Volcano
(also called Stratovolcanoes)
A composite volcano is a cone-shaped volcano built up from layers of lava and rock fragments. This volcano is steep near the top and flattens out near the bottom. A composite volcano can grow much larger than a cinder cone.
Composite volcanoes can have violent eruptions because the magma beneath it is high in silica, and hardened lava "plugs" often block crater openings. These plugs must be blown out of the way for other magma to escape.

10. Mount St. Helens in Washington State is a composite volcano that violently erupted in 1980.

11. Mount Redoubt in Alaska is also a composite volcano
Picture Date: March 21, Image Creator: Read, Cyrus;
Image courtesy of Alaska Volcano Observatory / U.S. Geological Survey

12. Images courtesy of the Alaska Volcano Observatory / U. S
Images courtesy of the Alaska Volcano Observatory / U.S. Geological Survey
Mount Redoubt
Picture Date: March 21, Image Creator: Read, Cyrus;

13. A shield volcano is shaped like a broad, flat dome.
It is built up of many eruptions of lava that is low in silica, so it flows easily and spreads out in thin layers.
Mauna Loa is a shield volcano that makes up most of the island of Hawaii.

14. Mauna Loa
Photo by J.D. Griggs

15. Lava Dome Volcano
A dome volcano has a single vent, or pipe form which the magma erupts. Thick, fast-cooling lava flows down the sides of the volcano to form a steep- sided volcano.
Volcanic domes commonly occur within the craters or on the flanks of large composite volcanoes. Here is a dome volcano in the crater of Mount St. Helens

16. Mono Craters Near Mono Lake In California's Eastern Sierra
Mono Craters Near Mono Lake In California's Eastern Sierra. These are lava domes.
Courtesy of the US Geological Survey

17. Caldera Volcano
A caldera is a huge crater formed by the collapse of a shield or composite volcano when magma rapidly erupts from underneath it. A violent eruption can empty much of the magma chamber, causing the volcano to collapse into it.

18. What is an eruption? When a volcano explodes it is called an eruption.
A volcanic eruption is one of the most powerful events in nature.

19. Inside a volcano A volcano is made up of long pipes called vents.
These vents are connected to a hole deep inside the Earth called a chamber. Inside the chamber the magma can be over F.

20. Where are volcanoes found?
Volcanoes are found along subducting convergent plate boundaries, divergent plate boundaries and at hot spots in the earth's surface.
The Ring of Fire which surrounds the Pacific plate includes many of the worlds most active and powerful volcanoes

21. Hot Spots
Continental Hotspots - In some places on Earth, the crust is very thin. A hot spot volcano forms when magma pushes through a thin part of the Earth’s crust and erupts onto the surface.
Example: Yellowstone
Ocean Hotspots -Many hot spots are underneath the ocean. These form underwater volcanoes that grow and form islands, such as the Hawaiian islands.

22. Volcanic Eruptions Volcanoes can be active, dormant or extinct.
An active volcano is one that has erupted in the last 10,000 years and will probably erupt again. An active volcano might be erupting or dormant.
An erupting volcano is an active volcano that is having an eruption...
A dormant volcano is an active volcano that is not erupting, but might at some time in the future.
An extinct volcano has not had an eruption for at least 10,000 years and is not expected to erupt again.

23. There are more than 1,500 active volcanoes in the world.
Map of the active volcanoes around the world.
Notice how the majority of volcanoes exist along the plate margins

24. Volcanic Eruptions -Scientists use special terms to describe the different kinds of volcanic eruptions.
Fissure Eruptions: Not all eruptions start with an explosion caused by gas pressure. Fissure eruptions occur when magma flows up through cracks in the ground and leaks out onto the surface
The gentlest eruptions are nonexplosive Hawaiian eruptions, named after the volcanoes found in Hawaii. In Hawaiian eruptions, lava erupts relatively quietly from one or more vents, producing quick-moving lava flows and lava fountains.

25. Strombolian eruptions, named after a volcano in Italy, are characterized by many small but relatively weak explosive eruptions. The eruptions occur in fairly short, regular bursts.
More explosive than a Strombolian eruption is a Vulcanian eruption, which produces large amounts of ash but few lava flows. It takes its name from the island of Vulcano in Italy.
A Peléean eruption, named after Mount Pelée in Martinique, is a violent explosion that is often accompanied by rapidly moving flows of ash, rock fragments, and gases.
Plinian eruptions are among the most powerful eruptions known. Named after Pliny the Elder, a famous Roman scholar killed during the eruption of Mount Vesuvius in A.D. 79, this type of eruption hurls plumes of ash tens of miles into the sky.

26. Volcanic Eruptions

27. Volcanic Eruption Index

28. These spheres represent the volume of erupted tephra for some of the most widely-known explosive volcanic eruptions. Although most people believe that Vesuvius (79 AD - the Pompeii eruption), Mount St. Helens (1980) and Mount Pinatubo (1991) were enormous, they are very small compared to ancient eruptions such as Wah Wha Springs, Toba, Yellowstone or Long Valley Caldera

29. Volcanic Materials - Magma and Lava
Volcanic Materials - Magma and Lava . Magma is molten rock beneath Earth's surface, that contains gases under pressure. Magma is less dense than the rock around it, so it rises toward Earth's surface. Once the magma stops, it can collect in a magma chamber. In that chamber it can harden into igneous rock, or erupt. If the magma erupts onto Earth's surface, it is then called lava. Sometimes lava flows down the outside of a volcano like a river. Other lava is thick and sticky and creeps forward only a few yards a day.

30. Magma that is high in the compound silica does not flow well.
As the magma rises, the expanding gases are trapped. Pressure builds until the gases blast out of the magma, causing a violent, dangerous eruption.
Volcanic rocks known as andesite and rhyolite form from high silica magmas that erupt from subduction zone volcanoes and continental hot spots such as Yellowstone.
Magma that is low in silica flows easily, allowing gas bubbles to escape and reduce the pressure.
An eruption may throw lava high into the air, creating a lava fountain, that people can usually watch safely nearby.
Basaltic volcanic rocks form from this type of eruption and commonly take place along mid-ocean ridges and at oceanic hot spots, such as Hawaii.

31. Different Types of Lava
Aa (AH-ah) is jagged, crumbly lava formed when the molten rock cools on contact with the air
Pahoehoe (pa-hoy-hoy) is a runny lava. As it cools, it forms a wrinkled skin that looks like coils of rope.

32. Pillow Lava
When magma wells up under the sea it cools and forms large bubbles of lava that look like stone pillows

33. Pele’s Hair
These are thin strands of lava named after the Hawaiian goddess of volcanoes.
Pele's Hair is formed when small gas pockets rise to the top of a lava flow.  When the bubble reach the surface, they "pop" sending streamers of lava into the air.  This lava cools quickly to form long, slender, golden strands of obsidian.

34. Volcanic Materials Volcanoes also erupt rock fragments.
The rock fragments are formed from small bits of magma, hardened lava, and rocks ripped from a volcano's walls during eruption.
The smallest rock fragments are volcanic ash, which are no bigger than rice grains. Ash can be carried long distances by winds.
Volcanic cinders are somewhat larger fragments. About the size of gravel.
Volcanic bombs and blocks are the largest, and can be as large as a house.

35. Rock Fragments

36. Volcanic Gases
Volcanic gases are made mostly of water vapor, carbon dioxide and sulfur dioxide . They can mix with ash to form what looks like smoke that rises from a volcano.

37. A pyroclastic flow is a dense cloud of super-hot gases and rock fragments that stays near the ground and races downhill from an explosion. It can be as hot as 1,830 °F and travel more than 450 mph.
A pyroclastic flow is the most dangerous type of volcanic eruption.

38. Volcanic gases and ash affect the air.
Volcanoes give off gases, released into the air, from magma before, during, and after an eruption. Some contain sulfur, such as hydrogen sulfide, which smells like rotten eggs. Other gases include sulfur dioxide and carbon dioxide, both of which can be fatal to animals and people in large quantities.
Some gases, such as sulfur dioxide, form acids when they mix with water in the air. These acids return to Earth as acid rain, snow, or sleet, which can damage forests and kill fish in lakes.
Large amounts of volcanic gases in the air can also change weather worldwide. Sulfur dioxide can combine with other gases in the atmosphere to form a haze around the entire planet. Volcanic ash can also be carried around the Earth by winds. The haze reduces the amount of sunlight reaching Earth, and the ash reflects sunlight. These can cause lower temperatures on Earth.

39. Volcanic activity affects water.
When water sinks down through the ground in an area where magma or hot rock is near Earth's surface, the water gets heated and then rises back to the surface at a hot spring. At most hot springs, water flows up into a calm pool.
A geyser is a hot spring in which water shoots from underground into the air. Countries with many hot springs and geysers can use them as a source of heat.
A fumarole is similar to a hot spring but releases steam and other gases instead of hot water.
Deep-sea vents are hot springs that form where the ocean floor is spreading. Cold seawater flows into cracks in the sea floor, is heated by hot rock and magma, then rises again. The water coming out is rich in dissolved minerals, which makes it look black. When the dissolved minerals hit colder water, they form into solid minerals again, building up the vent chimneys.

40. Lahar is an Indonesian term that describes a hot or cold mixture of water and rock fragments flowing down the slopes of a volcano and (or) river valleys.
When moving, a lahar looks like a mass of wet concrete that carries rock debris ranging in size from clay to boulders more than 10 m in diameter.

41. Geyser – Old Faithful in Yellowstone, National Park

42. Fumaroles escaping from Fourpeaked Volcano in Alaska

43. Hydrothermal Deep-sea vents

44. Effects of Volcanoes Created most the Earth’s land and our air.
Positive
Created most the Earth’s land and our air.
The dramatic scenery created by volcanic eruptions attracts tourists. This brings income to an area.
The lava and ash deposited during an eruption breaks down to provide valuable nutrients for the soil. This creates very fertile soil which is good for agriculture
The high level of heat and activity inside the Earth, close to a volcano, can provide opportunities for generating geothermal energy.
Negative
Many lives can be lost as a result of a volcanic eruption.
If the ash and mud from a volcanic eruption mix with rain water or melting snow, fast moving mudflows are created. These flows are called lahars.
Lava flows and lahars can destroy settlements and clear areas of woodland or agriculture.
Human and natural landscapes can be destroyed and changed forever.
Hugh eruptions can change the world’s weather by blocking out the sun and making the climate colder.
Gases released by volcanoes can be acidic and poisonous to living things.

45. Volcanoes in Space
There are volcanoes on many of the moons and planets in our Solar System.
The larges volcano in our solar system is not on Earth but on the planet Mars.
Olympus Mons is extinct volcano on Mars and is three times taller than Mount Everest, the tallest mountain on Earth’s surface.

46. Famous Volcanic Eruptions
Every year at least 50 volcanoes erupt somewhere in the world. Many of these eruptions are small but some are huge and cause great damage.
Here is a list of some famous volcanic eruptions

47. Unzen, Japan, 1792
Mount Unzen's biggest eruption happened way back in 1792, when, along with a related tsunami, it killed 15,000 people. The Japanese volcano was largely quiet for the next 200 years or so. And then Unzen began to rumble. It started to ooze lava a couple weeks before it violently erupted in 1991, killing 43 people, including a group of scientists and reporters, and forcing the evacuation of thousands of homes. It remained active, releasing lava and ash until about Since then, it's been getting some much-needed rest.

48. El Chichon, Mexico, 1982
How about a swim in a mountaintop lake? When El Chichon erupted in 1982, it killed 2,000 nearby residents in Chiapas, Mexico, and left behind a brooding, sulfuric, acidic lake that formed when the dome collapsed into a crater and filled with water. Probably not something you'd want to take a dip in. What's worse, no one saw the eruption coming. Most people thought that the volcano had long ago gone extinct, so when El Chichon belched out a "hello," it was quite the unpleasant surprise. Like other large volcanic explosions, the ash sent into the atmosphere had a worldwide atmospheric effect, leading to cooler temperatures across the globe, along with a nice bonus in the form of some particularly colorful sunrises and sunsets.

49. Mt. Pinatubo, Philippines, 1991
The 1991 eruption of Mount Pinatubo, in the Philippines, was the second largest eruption of the 20th century, with a volcanic explosivity index rating of 6. That puts it somewhere in Krakatoa territory: bigger than Mount St. Helens' in 1980, but smaller than Tambora in 1815.
Pinatubo finally exploded on June 15, tossing out some two and a half cubic miles of material, including rock, ash and toxic fumes. Some 800 people died as a result of the eruption, which left a mile-wide crater lake at the summit

50. Mount St. Helens, United States, 1980
The May 18, 1980, explosion of Mount St. Helens was the United States' deadliest and most destructive volcanic event, with 57 lives lost. The massive eruption, complete with a 15-mile-high ash plume, was preceded by a 5.1 magnitude earthquake, which caused a large chunk of the mountain to slide away. The volcano erupted violently for nine hours, taking Mount St. Helens from a symmetrical, dome-shaped, snow-capped peak to a topless mountain sporting a massive crater. Quite the makeover. The volcano has continued to belch steam and even magma since the eruption as it slowly rebuilds its dome.

51. Nevada del Ruiz, Colombia, 1985
When this Colombian volcano erupted in 1985, it killed 23,000 in the nearby village of Armero, making it the second deadliest volcanic eruption in the 20th century. Many were asleep during the nighttime eruption, which triggered a destructive mudslide-like flow of lava, mud and volcanic debris known as a lahar, amplified as the mountain's glaciers melted. And make no mistake, This volcano was a repeat offender, having taken out villages more than once during eruptions over the past several hundred years. Today, Nevada del Ruiz still poses a threat and thus retains its old nickname, "the sleeping lion."

52. Kilauea, United States, 1983 - present (continuous)
Kilauea (the name means "spewing" or "much spreading") may not be the most explosive or violent or destructive volcano, but give it credit for some staying power: the Hawaiian volcano has been erupting continuously for over 20 years now, making it one of the world's most active volcanoes. The current lava—spewing eruption started way back in 1983, when Ronald Reagan was president and blackberries were just things you ate. The volcano is said to be home of the Hawaiian volcano goddess, so maybe she's just been really fired up about something these past few decades. But just because it's a slow, steady eruption doesn't mean Kilauea hasn't caused some damage: The eruption has consumed a couple small towns and a stretch of highway and it's added nearly a square mile of land mass to the island of Hawaii as its lava spills into the Pacific. Just last year, Kilauea even exploded, throwing a bit of ash and gas out into the air.

53. Vesuvius, Italy, 79
When Mt. Vesuvius blew in A.D. 79, it left the entire city of Pompeii frozen in time, buried under a shroud of ash and pumice that rained down for nearly an entire day as the volcano raged. The 25,000 or so people that it buried were preserved for archaeologists to one day study and the volcano itself has now also been extensively studied. It's erupted over a dozen times since the burial of Pompeii, most recently in Since the area surrounding it in Italy is now pretty densely populated, let's hope it doesn't do that again any time soon.

54. Mt. Pelee, Martinique, 1902
When Mt. Pelée exploded on the Caribbean island of Martinique in 1902, it killed 29,000 people and destroyed the entire city of St. Pierre. The residents had been watching the volcano shoot steam and sulfurous fumes into the air for several days, but on May 8, Pelée finally went in a terrifying display. Witnesses on ships just off its coast described a sudden massive mushroom cloud, filled with fiery hot ash and volcanic gases, consuming the island in seconds. Only two people survived the explosion, one of them a prisoner in a jail cell who was saved by his poorly ventilated, cavern-like accommodations.

55. Krakatoa (Krakatau), Indonesia, 1883
When Krakatoa blew its top in 1883, it did so with the force of 13,000 atomic bombs. They heard the Indonesian island go all the way in Australia, and tsunamis, ashes and toxic fumes overtook entire islands nearby. All in all, over 36,000 people lost their lives and whole villages just went away. The shockwave reverberated around the globe, registering on barographs thousands of miles away. The 1883 eruption destroyed almost the entire island, but, lest there be any doubt that the area is still active, a new island, dubbed Anak Krakatau ("child of Krakatau") has risen in its place ... and it gets bigger every day

56. Tambora, Indonesia, 1815
Tambora was the biggest volcanic eruption ever recorded. It was so big, in fact, that it canceled summer. That's right, no summer. So much ash was thrown into the atmosphere when Tambora exploded in 1815 that it effectively blocked out sunlight and solar radiation, reflecting it back out away from our planet, which started getting kind of chilly and cloudy as a result. Thus, 1816 became the year without a summer. Way off in Europe and the United States crops failed and people starved, while back in Indonesia 10,000 people were killed nearly instantly by lava flows and toxic fumes. The overall death toll from the explosion and resulting tsunami was 92,000.

57. The Deadliest Volcanic Eruptions
Volcano
Year
Deaths
Major cause of deaths
Tambora, Indonesia
1815
92,000
Starvation
Krakatau, Indonesia
1883
36,417
Tsunami
Mount Pelee, Martinique
1902
29,025
Ash flows
Ruiz, Colombia
1985
25,000
Mudflows
Unzen, Japan
1792
14,300
Volcano collapse, tsunami
Laki, Iceland
1783
9,350
Kelut, Indonesia
1919
5,110
Galunggung, Indonesia
1882
4,011
Vesuvius, Italy
1631
3,500
Mudflows, lava flows 79
3,360
Ash flows and falls
Papandayan, Indonesia
1772
2,957
Lamington, Papua New Guinea
1951
2,942
El Chichon, Mexico
1982
2,000