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Physical Geology 101 10. Volcanoes I (p. 126-149) Volcano Statistics How many volcanoes erupt on land or in shallow water every year? ____________ How many volcanoes have erupted in the USA in the past 200 years? ___________ How many volcanoes in the world emit rocks, ash, gas or lava every day? ___________ Examples of 5 volcanoes that have shown eruptive activity in the past week: _______________________ _______________________ _______________________ _______________________ _______________________ How many active volcanoes are there in the world? ___________ How many people live on or near these volcanoes? _______________ In the past 500 years, there have been 7 catastrophic eruptions that have killed more than ____________ people at a time. Since 1800, there have been 19 eruptions that have killed more than 1,000 people. Potential volcanic hazards: __________________ – e.g. Hawaii, Iceland, Democratic Republic of Congo, Mexico __________________ – e.g. Galeras, Colombia __________________ – e.g. Mt. Vesuvius, AD79; Mt. St. Helens, 1980; Pinatubo, 1991 __________________ – effects: respiratory ailments and collapsed roofs; e.g. Pinatubo __________________ – e.g. Lake Nyos, Cameroon, 1986 – 1,700 people killed __________________ – e.g. Armero, Colombia, 1985 – 25,000 killed; Mt. Rainier, WA. __________________ – pyroclastics, rocks, trees, etc. - e.g. Nevado del Ruiz, Colombia __________________ – e.g. Krakatau, Indonesia, 1883 – eruption created a tsunami that killed >35,000 people. __________________ – e.g. Kalapana, Hawaii, 1975 (also caused a tsunami) Additional causes of death in the long-term: _________________________________ The most destructive known volcanic episode happened about 251 million years ago in Russia, forming a large region of basalt lava flows called the _______________________. The lava from that eruption covered a million square miles and resulted in the death of 90% of all sea life and 70% of all land creatures- an extinction level event of global proportions. Since then, there have been 9 other enormous floods of basalt onto the Earth's surface. Which flood basalt event happened about 16 million years ago in the Pacific NW? 1 Physical Geology 101 ____________________________________________ Types of Eruptions The two types of eruptions are ______________________ and ____________________. Nonexplosive Eruptions What location typically experiences nonexplosive eruptions? _________________ What is the largest volcano on Earth? _____________________ What are the viscosity and silica content characteristics of lava that generally produces nonexplosive eruptions? Viscosity: HIGH or LOW ? Silica content: HIGH or LOW ? What type of lava would have these characteristics? ______________________ Gases spattering out of a volcanic vent produce a ____________________. The most active volcano on Earth is __________________, with >50 eruptions since 1823. Mafic lava that erupts nonexplosively can flow great distances, and eventually builds up a type of volcano called a _____________________. Such volcanoes typically have very wide bases and gently sloping sides. Examples of shield volcano locations: ___________________ ____________________ ____________________.. Where are fissure eruptions common (also nonexplosive)? ______________________ ______________________ ______________________ ______________________ Explosive Eruptions What are the viscosity and silica content characteristics of lava that generally produces explosive eruptions? Viscosity: HIGH or LOW ? Silica content: HIGH or LOW ? What type of lava would have these characteristics? ___________________________ Explosive eruptions results in huge volumes of pyroclastic material and gases being forced up into the atmosphere in the shape of a huge column called a ______________________. How high can these columns reach? ________________ 2 Physical Geology 101 Examples: ______________________ and _______________________. When the pyroclastic material first gets ejected sideways from the volcano, the type of eruption is called a _____________________ (happened at Mt. St. Helens in 1980). Sometimes, volcanic material can rush down the slopes of the volcano just like an avalanche, and is called a _________________________. It contains extremely hot bits of semi-molten rock, called ___________, as well as huge volumes of poisonous gases. What are the three types of tephra (from biggest to smallest particles)? ______________________________ ______________________________ ______________________________ The lava from explosive eruptions is silica-rich and very viscous so it doesn’t flow far. Along with pyroclastic flows, it builds up a multilayered, steep-sided volcano called a: __________________________ ; also called a _____________________________ Examples of stratovolcanoes: ___________________ and _____________________ Volcanic Features There are a number of types of features on Earth that formed through volcanic processes. Cinder Cones Cinder cones are built from blobs of congealed lava and lapilli size pyroclastic material ejected from a volcanic vent that fall to the ground as cinders or clinkers. This material collects in a heap around the vent, forming a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their surroundings. They form due to a single, short-lived eruptive event. Example from Idaho: ________________________________ Craters and Calderas A crater is a funnel-shaped depression that exists at the top of most volcanoes. What is a caldera? _______________________________________________________ Example of a caldera in the Cascades: ______________________________ Tuff Rings and Maar Craters Explosive eruptions of pyroclastic material may leave a ring of debris around a vent, called a tuff ring. Example: ____________________________ 3 Physical Geology 101 Similar explosive eruptions may occur when lava flows cover over a lake, forming a circular depression at the surface called a maar crater, surrounded by ejecta and which may fill with water to form a circular lake. Lava Domes After an eruption, a volcano doesn't necessarily become inactive. It may start to push up the crater or caldera, forming a mound called a lava dome. Examples: ________________________ and ________________________ What is the world’s largest lava dome? __________________________ Predicting Eruptions What are the three categories for volcano activity? 1. __________________ (is erupting or has erupted in recent history) 2. __________________ (has not erupted in recent history but has the potential to erupt) 3. __________________ (shows no signs of activity) Some tell-tale signs of an impending eruption include: 1. 2. 3. 4. Sudden bulging inside the crater due to the magma chamber filling up (measured with a tiltmeter). Increased minor earthquake activity. Increased water temperature in the crater lake. Increased gaseous emissions. FINAL QUESTION: What is the most active volcano in the Cascades? __________________________________ 4