Volcanoes For the Advanced Earth and Space Science Student

Types of Volcanic Eruptions  Divergent boundaries,  most frequently at mid-ocean ridges

Types of Volcanic Eruptions  Subduction Boundary  - result from melting subducting crust; most active volcanic chain in Indonesia, Andes Mt, Cascade Mts.

Cascade Mts.  cascades cascades mt. st. helens

Types of Volcanic Eruptions  Hot Spots- found within plates, like the Hawaiian Islands and Yellowstone Park

Magma  Magma- underground molten (melted) rock  Magma is extremely hot (500 to 2,000` C )  less dense than surrounding rock, so it rises to the surface through an opening called a volcano  The rate at which magma moves is mainly determined by its silica content  Silicon is the second most abundant element in the Earth’s crust

Types of Magma  Felsic magma- thick, lightly colored, slow moving magma; high silica content (60%-80%)  Mafic magma- thin, darker in color, and faster moving magma; relatively low silica content (50% or under)

Lava  Magma becomes LAVA when it reaches the surface

Explosivity of Eruptions  Mafic magma is thinner and can move faster; gases dissolved in this type of magma can escape easily.  As a result, lava pours out smoothly on the surface forming shield volcanoes

Explosivity of Eruptions  Felsic magma is thick (viscous) and moves much slower; gases cannot move easily; as a result, lava hardens and plugs the neck often explodes in a violent eruption emiting ash, tuft, cinders, and bombs

Resulting Formations  Felsic magma is thicker and creates an explosive eruption that results in a steep-sided cone called a CINDER CONE.

Mt. Pelee, West Indies  The destruction was caused by a nuee ardente (hot, poisonous gasses and ash).  Mt. Pelee is famous for the 1902 eruption which killed 29,000 people and destroyed the city of St. Pierre. This is the largest number of casualties for a volcanic eruption this century

nuée ardente  When viscous magma containing much gas is erupted, a glowing cloud containing ash and pumice may be thrown into the air. This cloud will fall back onto the earth like an avalanche before it can cool off. This avalanche is called a nuée ardente. viscousmagmagasash pumiceviscousmagmagasash pumice  Nuées ardentes are often the biggest killers. The direct translation of nuée ardente is "incandescent cloud", however "glowing avalanche" is perhaps a better description.  Nuées ardentes reach speeds up to 300mph.  Nuées ardentes reach speeds up to 300mph.

Mt. Vesuvius Italy Mt. Vesuvius Italy  Vesuvius has erupted about three dozen times since 79 A.D., most recently from  Herculaneum was buried under 75 feet of ash

 About 10 feet (3 m) of ash fell on Pompeii, burying everything except the roofs of some buildings. The city was abandoned and its location forgotten. In 1595, excavations discovered artifacts at Pompeii. Archeological excavations began in the mid- nineteenth century. There are numerous molds of people in their final moments.

Mt. Fuji Fuji has erupted at least 16 times since 781 AD. Most of these eruptions were moderate to moderate-large in size. The crater on the flank was created by the 1707 eruption. The crater on the flank was created by the 1707 eruption.

Tambora, Indonesia  The 1815 eruption of Tambora was the largest eruption in recorded history. It was 150 times greater than the 1980 eruption of Mount St. Helens. Ash fell as far as 800 miles from the volcano.  92,000 people were killed by the eruption. About 10,000 direct deaths were caused by bomb impacts, ash fall, and pyroclastic flows. An estimated 82,000 were killed around the world indirectly by starvation, disease, and hunger from the global ash cloud that affected the weather.

Tambora, Indonesia  The eruption created global  climate changes; 1816 became  known as the Year Without a  Summer when snow fell during June and frost was still widespread during the month of July.  In the Northern Hemisphere, agricultural crops failed and livestock died, resulting in the worst famine of the 19th century. Europe experienced widespread crop failures and had a great famine.

TobaToba, Indonesia supervolcano Toba 70,000 to 75,000 years ago 70,000 to 75,000 years ago Estimated largest eruption in the last 2 million years. Estimated largest eruption in the last 2 million years. released energy equivalent to about one gigaton of TNT released energy equivalent to about one gigaton of TNT reduced global temperature; may have triggered an ice age. reduced global temperature; may have triggered an ice age. reduced the world's human population to 10,000 due to starvation. reduced the world's human population to 10,000 due to starvation. almost cause human extinction !!!!!! almost cause human extinction !!!!!!