Volcanoes

Magma Simple put, a volcano occurs when magma erupts onto the surface (land or under the ocean) Magmas originate at depths between 50 and 250 kilometers (30 to 150 miles) beneath the crust

Source of Magma Magmas can reach the surface in one of three plate tectonic settings: Divergent plate boundaries Subduction zones “Hot spots”

Types of Volcanoes Common types of magma eruptions Shield volcano Cinder cones Composite volcano Caldera Fissure Flood basalt

Shield Volcano Non-explosive eruptions of dark, fluid, basaltic magma high in Fe and Mg. Low viscosity of the magma allows for the flow off the mountain making the shield shape. Example: Mauna Kea, Mauna Loa, Hualalai, and Kilauea which make up the “big island” of Hawaii.

Shield Volcanoes Low silica level Low viscosity Lava High or low levels of gas Flattened mound Resembles a warrior’s shield

Composite or Stratovolcano Explosive andesitic viscous magma rich in silica that is layered with lava and rock from old eruptions. Periods of inactivity followed by huge, violent explosions.

Composite Volcanoes High in silica High viscosity magma High levels of gas Highly explosive Cone shaped Formed by layers of lava and ash

Cinder Cone Volcano Non-explosive eruptions of basaltic magma high in iron. Produces tephra (ash, dust, rocks, & lava bombs). Steep sided with a conical shape. Very common type of volcano. Example: Paricutin, Mexico. This volcano erupted in a field in 1943.

Cindercones Low silica lava High levels of gas “Fire-fountain” eruptions Commonly found on the flanks of shield volcanoes Made from a pile of rock pieces Structurally weak

Mount St. Helens Mount St. Helens in Washington is a composite volcano On March 16, 1980 the first of a series of minor earthquakes occurred under the volcano This marked the beginning of a new eruption cycle It had been ~350 years since the last eruption

ON YOUR PHYSICAL MAP, OUTLINE ALL OF THE COUNTRIES THAT TOUCHES THE PACIFIC OCEAN. ALONG YOUR OUTLINE, DRAW A VOLCANO SYMBOL.

Mid-Ocean Ridge/Underwater Divergent boundary produces usually fluid basaltic magma. Large rifts may erupt volumes of lava. Underwater pillow lavas may form. Pillow lavas above, Black smoker at mid- ocean ridge, & Iceland erupts

There are more than a million seamounts in the oceans (only a couple thousand are plotted on the map below) So there are far more volcanoes under the sea than on land Seamounts

The Hawaiian Islands are the classic example of hot spot volcanism Hot Spot Volcanism

Every island in the Hawaiian Island chain was created by volcanic eruptions that occurred as the Pacific Oceanic Plate crossed over a hot spot

Hot Spot Volcanism

The plate has moved to the northwest for more than 65 million years The big island of Hawaii is now over the hot spot

TOPS Top 10 Geography in conjunction with Main areas of hot spot activity globally

Continental Volcanic Hot Spots Yellowstone Caldera Chain formed as the North America Plate moved to the west southwest The ages of the Yellowstone Calderas formed over the hot spot range from 16 million years ago to the present

Continental Volcanic Hot Spots Currently, volcanic activity is exhibited only via numerous geothermal vents, including Old Faithful Geyser, but within the past two million years, it has undergone three extremely large explosive eruptions, up to 2,500 times the size of the 1980 Mount St. Helens eruption

Continental Volcanic Hot Spots The brown area marks the extent of the ash fall

Volcanic Hazards

1815Indonesia92,000 killed 1822Indonesia 5,500 killed 1826Indonesia 3,000 killed 1883Indonesia36,417 killed 1902Martinique29,025 killed 1902Guatemala 6,000 killed 1919Indonesia 5,110 killed 1951New Guinea 2,942 killed 1982Mexico 1,700 killed 1985Columbia23,000 killed How Bad Can It Be?

Causes of volcanic- related deaths Over the last 2,000 years How Bad Can It Be?

Pyroclastic material is volcanic ejecta violently blown out of the volcano into the atmosphere during an eruption It can be molten, partially molten or solid, with heated gases Pyroclastic Material

Basaltic Lava Types Pahoehoe is “smoother” lava at the surface, while A’a lava is a rougher more viscous rocky lava that crumbles as it flows. A sampling of Hawaiian lava A’a crumbles over an older pahoehoe flow

Projectile Volcanic Products Ash, tephra, lava bombs, lapilli, pele’s tears, cinder, pumice, and other volcanic products may be ejected through the air.

Volcanic Bomb

Pyroclasts Pyroclasts are classified by the size of the particle Volcanic ash is very fine dust which is “ash-like” in consistency Cinder is composed of gravel-sized pieces of ejecta and usually feels rough to the touch Volcanic bombs are large fragments of ejected magma which become rounded and cool (solidify) as they fly thru the atmosphere

Pyroclastic Flow For example, eruption of Vesuvius in 79 AD destroyed the city of Pompeii

Pompeii (79AD) On August 24, 79AD Mount Vesuvius literally blew its top, erupting tonnes of molten ash, pumice and sulfuric gas miles into the atmosphere. Pyroclastic flows flowed over the city of Pompeii and surrounding areas.

Pompeii (79AD) Pyroclastic flows of poisonous gas and hot volcanic debris engulfed the cities of Pompeii, Herculaneum and Stabiae suffocating the inhabitants and burying the buildings.

Pompeii (79AD) The cities remained buried and undiscovered for almost 1700 years until excavation began in These excavations continue today and provide insight into life during the Roman Empire.

Vesuvius today Vesuvius remains a hazardous volcano with heavily populated flanks: –around 1.5 million people live in the city of Naples alone –Naples is situated approx. 30 km from Vesuvius –Pyroclastic flows can flow up to 100 km from source! Bay of Naples Vesuvius Naples Courtesy of

Gases Sulfur dioxide (SO2) Hydrogen sulfide (H2S) Carbon dioxide (CO2) Hydrogen Chloride (HCl) Hydrogen Fluoride (HF) Volcanoes can also eject great quantities of gases and steam which can be mixed with the pyroclasts

Lahar Lahars are formed by the sudden mixing of large volumes of pyroclastic material, such as ash, with water For example, when volcanic activity melts a glacier on a mountain top, or because of heavy rain, or the draining of a lake in a crater

Lahar Lahars can flow very fast, at speeds faster than 100 kilometers per hour (60 miles per hour) They can flood large areas and flow for long distances in river channels Lahar in the Belham Valley, Montserrat, in the Caribbean, during heavy rain, 19 July 2007

Nuée Ardente A poetic-sounding French word introduced in 1904 to describe the terrible pyroclastic flow that destroyed the entire city of St. Pierre on the island of Martinique in 1902 It translates to “glowing incandescence”

Nuée Ardente Nuée ardente are extremely fast moving fluidized bodies of very hot gas, ash and rock that hug the ground as they flow down the volcanic slope Temperatures can be as high as 800 o C

Mount St. Helens On May 18, 1980, at 8:32 am, a magnitude 5.1 earthquake occurred 1 mile directly under the volcano 10 seconds later, the north side of the volcano began to collapse followed immediately by an explosion that blew the top 400 meters (1300 feet) off of the peak (a volume of 1.3 cubic kilometers)

Mount St. Helens Ash Fall

Mount St. Helens Mount St. Helens is now a volcanic national monument and remains active

1902 Martinique With each passing day, the eruptions became worse The French governor refused to evacuate the city of St. Pierre and surrounding smaller cities at the base of the volcano On Wednesday, May 7, 1902, the governor with his family and entourage visited St. Pierre There was a gala ball that night

1902 Martinique Martinique is an island formed by volcanoes in the Caribbean It was a French colony The dormant Mount Pelée volcano began a new series of eruptions on April 25, 1902

1902 Martinique The next day at 8:02 am, the city of St. Pierre was destroyed by a pyroclastic flow that roared down the slopes of Mount Pelée at of 670 kilometers per hour (415 miles per hour)

1902 Martinique Over 29,000 people are burned alive in seconds The entire town was completely destroyed

1902 Martinique Supposedly, there was one lone survivor, Louis- Auguste Cyparis (aka Ludger Sylbaris), who was in jail either for murder or being drunk He joined the circus

2007 Martinique Today, Martinique is an overseas department of France and St. Pierre is a quaint tourist attraction Mount Pele

Santorini Santorini is a circular group of islands in the Aegean Sea and is part of Greece The central lagoon is a volcanic caldera 12 by 7 kilometers (8 by 4 miles) in size

Mount Tambora (or Tomboro) is an active stratovolcano on Sumbawa island, Indonesia It was thought to be 14,000 feet (4,300 meters) high when it blew up in April 1815 The death toll was at least 71,000 people (some estimate 92,000 people were killed), of which 11,000 to 12,000 were killed directly by the eruption Mount Tambora

The explosion was heard on Sumatra island 2,000 kilometers (1,200 miles) away The red areas outlines the heavy ash fall Mount Tambora

1816 became known as the Year Without a Summer and the Poverty Year and Eighteen hundred and Froze to Death Agricultural crops failed and livestock died in much of the Northern Hemisphere, resulting in the worst famine of the 19th century Year Without a Summer Europe, still recuperating from the Napoleonic Wars, suffered from food shortages