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Transcript of Volcanoes
What causes Volcanic Eruptions?
Density & Pressure
Temperature in Earth's mantle is so hot that the upper mantle and crust melts and forms magma
Magma is lighter & more buoyant than surrounding rock so it rises
Gas forms as it rises
Pressure decreases and gas wants to escape
Sometimes it not only finds cracks in the Earth (tectonic plates, etc.), but makes cracks of its own
Cinder Cone (Scoria Cone) Volcanoes
Smallest <300m and most common
Made of loose, grainy 'cinders' that have blasted out of the vent at high velocity
When erupts, it shoots magma that cools quickly (Strombolian eruptions)
Usually erupts only once
Sometimes emits lava
Found on flanks of shield and composite volcanoes
Can be found in groups
Ex: Little Lake Volcano in California, Parícutin in Mexico, Near the Hawaiian Island volcanoes
HLTH 422 Dr. Johnston
Brianne Johnson, Scott Johnson, Jessica Sagisi, Flo Toleafoa, Nate Tanner
Volcanoes are openings in the earth's crust that allow molten rock from Earth's mantle to flow out onto the surface as lava. They emit vast amounts of gas, such as carbon dioxide, water vapor and sulfur dioxide.
Composite Volcanoes (Stratovolcanoes)
Giant crack in ground -- no central crater
Usually surface is mostly flat after eruption
Not point source but several sites along a linear fracture
Not restricted to any specific area
Along the Mid-Atlantic ridge, which is an active site for fissure eruptions because the plates are moving apart
Most are not visible because they are on the ocean floor
Also common along flanks of large volcanoes
Ex. Las Pilas in Nicaragua, Iceland, Hawaii
Rift or "Fissure" Volcanoes
And Plate Tectonics
These eruptions are characterized by quick, explosive bursts that can shoot 20 km up into the air. Incandescent rock bomb fragments (greater than 64 mm) and ash are expelled from these volcanoes, with minimal lava flow towards the end of the eruption.
A commonly cited example of a Strombolian Eruption is the Paricutin eruption 200 miles away from Mexico City. This volcano grew from a 2.5 meter wide fissure on a cornfield into a 100 meter cone in one week! The accumulation of rock bombs and other pyroclastic material led to the rapid build-up. After 9 years of intermittent eruption, the volcano had completely burned and covered the village of Paricutin, resting as a cone at 424 meters tall.
Paricutin Eruption, 1943
Types of Eruptions
When Krakatau (the volcano pictured) erupted near Indonesia in 1883, the explosion of tephra (rock fragments and particles) was so forceful that the material spread over 2500 km away from the volcano. However, the resulting dust cloud covered most of the earth's atmosphere, blocking the sun and causing lower temperatures worldwide for the next 5 years. Because pyroclastic flows are less dense than water, the flows traveled across the ocean's surface to Sumatra, 48 km away. As magma vacated the magma chamber and upper mantle, 2/3 of the island collapsed, causing tsunamis that engulfed nearby islands. Between the eruption and tsunamis, there were over 36,000 people killed in this disaster.
Pyroclastic Flow Information Video- http://science.howstuffworks.com/nature/7153-volcanoes-pyroclastic-flow-video.htm
These eruptions are much more explosive and dangerous than Strombolian eruptions.
Because of more viscous magma, gases are trapped, resulting in a higher pressure build-up.
This leads to more powerful explosions, with eruptive columns between 5 and 10 km in height.
The eruption contains large rock bombs, but due to the powerful nature of the explosion, most of the material expelled from the volcano is pulverized into a very fine dust.
Pyroclastic flows can occur as a result of column collapse.
Also known as "hydrovolcanic" eruptions, Surtseyan Eruptions are the result of the interaction between ground/ surface water and magma.
The creation of steam creates pressure that results in an eruption more explosive than the Strombolian eruption.
The typical tephra of a Surtseyan eruption are basaltic ash and lapilli (small rocks between 2 and 64 mm)
Surtseyan eruptions are named the type of eruption that led to the creation of the island of Surtsey in 1965 just south of Iceland. This eruption occurred mostly underwater over the course of 2 years. When island broke the surface of the ocean, water could no longer interact with the magma and the eruption became Hawaiian and Strombolian.
Hawaiian eruptions shoot jets hundreds of feet in the air containing lava through fissures on the summit and sides of these volcanoes.
Because of the fluid nature of lava in these eruptions, flows can travel for several miles before cooling and hardening. Lava flow is NOT the same thing as pyroclastic flow! The hardening and deposition of lava increases the height of volcanoes.
Lava will often flow to a depressed area and settle, forming a lava lake (pictured above)
Expected and Unexpected Dangers
Hawaiian eruptions are appealing to tourists because of the lack of ash and other materials being expelled from an erupting volcano. However, there have been reports of people being killed - not by lava flows or falling rock, but by toxic gases. Lava and its interaction with sea water can result in the release of toxic substances, including carbon dioxide, sulfur dioxide, hydrogen sulfide and hydrofluoric acid.
The lava flow of a Hawaiian eruption from Kilauea overtook the small coastal town of Kalapana, Hawaii in 1950. After traveling some 14 miles, lava from a Hawaiian eruption destroyed their homes and covered their community in 50 feet of cooled lava. Fortunately, the lava flow was slow enough to be detected. An evacuation was initiated, and no deaths occurred.
Vesuvian/ Plinian Eruptions
Rather than having sporadic explosions, Plinian eruptions have a sustained column of ash being released into the air during eruptions. These eruptions can last from hours long to weeks.
There are generally large tephra deposits (especially ash), pyroclastic flows, and lahars (volcanic mudslides that occur because of volcanic material mixing with water from snow). These features make Vesuvian eruptions the most dangerous type of eruption.
The Mount Vesuvius eruption (pictured right) is the namesake of this type of eruption. In 79 AD, Vesuvius erupted, completely covering the cities of Pompeii and Herculaneum in 23 ft. of pumice and ash because of pyroclastic flows. Some 16,000 people died. Since 79 AD, Vesuvius has erupted 50 times with many deaths because people continue to build around it. Today, there are 3 million people living near Vesuvius that could be affected by an eruption.
"Rift Zone" on Kilauea
Volcanic eruptions in their many forms have been known to leave a wake of other disasters:
These disasters include:
Poisonous gas emissions
Volcanic earthquakes and tremors
Famine & disease
Laki, Iceland 1789
Mount Tambora, Indonesia 1815
Mount Pelee, Martinique 1902
Mount St. Helens, Washington 1980
Other Volcanic Eruptions:
Unzen, Japan 1972
Nevada del Ruiz, Columbia 1982
Lake Nyos, Cameroon 1986
Mount Pinatubo 1991
Soufriere Hills, Caribbean 1995- present
Democratic Republic of Congo 2002
Volcanic Explosivity Index (VEI)
1. Small earthquakes
2. Temperatures increase
3. High sulfur content
How often: daily
How often: weekly
Classification: Strombolian/ Vulcanian
How often: 10s of years
Classification: Vulcanian/ Plinian
How often: 100s of years
Classification: Plinian/ Ultra-Plinian
Water levels and chemistry
How often: daily
How often: yearly
How often: 100s of years
How often: 1000s of years
How often: 10000s of years
USGS Volcanic Activity Alert-Notification System
Lower slopes are gentle but rise steeply, small crater
Made of layers of hardened lava and ash
Looks like beautiful mountains but most deadly of the volcanoes
Usually violent eruptions (Plinian/Vesuvian eruptions)
Erupt infrequently--about 100 yr intervals
Many on earth, typically near subduction zones . Usually in chains. Notably around the Pacific Rim, a.k.a. "The Ring of Fire."
Ex. Mt. Vesuvius, Mt. Fuji, Mount St. Helens
- Exhibits typical background activity
- steaming, seismic events, thermal events, degassing
Mammoth Mountain, California
- Exhibiting signs of elevated unrest above known background activity
- Low level seismic tremors
- After a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase
Veniaminof Volcano, Alaska
- Exhibiting heightened or escalating unrest with increased potential of eruption, time frame uncertain OR an eruption is underway that poses limited hazards including no or minor volcanic-ash emissions
- Major eruption is imminent, underway, or suspected with hazardous activity both on the ground and in the air
Redoubt Volcano, Alaska
What to Do During a Volcanic Eruption
- Follow the evacuation order issued by authorities.
- Avoid areas downwind and river valleys downstream of the volcano.
- Listen to a battery-operated radio or television for the latest emergency information.
If caught indoors:
1. Close all windows, doors, and dampers
2. Put all machinery inside a garage or barn
3. Bring animals and livestock into closed shelters
- Seek shelter indoors.
- If caught in a rockfall, roll into a ball to protect your head.
- If caught near a stream, be aware of mudflows. Move up slope, especially if you hear the roar of a mudflow.
If trapped outdoors:
Protect during Ashfall
1. Wear long-sleeved shirts & long pants
2. Use goggles to protect your eyes
3. Use a dust mask or hold a damp cloth over your face to help breathing
Lasted nearly a year: released 15 cubic km of lava over 8 months. Caused famine, drought, and gas poisoning in the Northern Hemisphere and killed 9350 people.
Eruption in 1805 with a massive VEI of 7. Killed over 80,000 people due to pyroclastic flows, tsunamis, famine, disease and starvation.
Wiped out an entire population of 30,000 except for two survivors
Tambora to Vermont
Joseph Smith History 1:3 - "My father, Joseph Smith, Sen., left the State of Vermont, and moved to Palmyra, ...when I was in my tenth year, or thereabouts."
Due to the volcanic winter, and the poor harvest, caused by the eruption of Mount Tambora, Joseph Smith's family moved to New York.
Volume of erupted pyroclastic material
Height of eruption column
Duration of hours
Qualitative descriptive terms
Large craters, low slopes
Formed by lava of low viscosity (basaltic lava)
Result of high magma supply rates
in middle of tectonic plates due to a hole (hot spots) or along subduction volcanic arcs
Ex. Island of Hawai'i--Kilauea, Mauna Loa, Galápagos Islands--Fernandina
Subduction Volcanic Arcs
How to Prepare for Eruptions
1. Learn about your community warning systems & emergency plans
2. Be prepared for the hazards that can accompany volcanoes
3. Make evacuation plans
4. Develop an emergency communication plan
5. Have disaster supplies on hand
Run like Pierce!
Mount Marapi Eruption, Indonesia, 2010
More on Pyroclastic Flow
Pyroclastic Flow occurs as a dense column of gas and volcanic ash and dust collapses on itself because of its high density. It is an avalanche of hot, toxic gas and solid to semi-solid fragments (everything between dust and rock bombs) rushing down the slope of the volcano at speeds often exceeding 100 miles per hour. It is the deadliest of all volcanic activity. As the flow is less dense than water, it can float across water, as when Krakatoa erupted.
You should look up a youtube video called "Pyroclastic Musical Flow." It gives a pretty good image of what a pyroclastic flow is like. Sorry about the weird music!