V OLCANOES Chapter 11 Section 11-2

V OLCANO The place where magma reaches the Earth’s surface

V ENT Vent - The opening from which lava erupts

Crater – funnel shaped pit or depression at the top of a volcano cone

4 M AJOR T YPES OF L AVA Type 1 Dark colored Contains lots of water Rich in iron and magnesium When this lava cools, igneous rocks such as basalt are formed Type 2 Light in color Contains little water Rich in silicon and aluminum Compounds of these elements account for the light color When this lava cools, it forms the igneous rock rhyolite

4 M AJOR T YPES OF L AVA Type 3 Chemical composition close to the dark colored type and light colored type Andesite is an example of the igneous rocks formed Type 4 Contain large amounts of gases such as steam and carbon dioxide Forms rocks with many holes as lava cools because gas bubbles are trapped Examples are Scoria and Pumice

During volcanic eruptions, many rock fragments are blown in the air. VOLCANIC DUST: very fine Less than.25 millimeter in diameter Tiny as grains of flour VOLCANIC ASH: Particle size is between.25mm to 5 mm 5 mm is the size of rice grains VOLCANIC BOMBS: Centimeter to a meter in size. Cinders are volcanic bombs the size of golf balls

Types of Volcanoes

Cinder Cones Form from explosive eruptions of rock particles Low cone, narrow base, steep sides Paricutin, Mexico Volcanoes that consist predominantly of pyroclastic materials are called cinder cones. These mountains, such as Capulin Mountain in New Mexico (USA), are easily eroded and usually do not reach great heights. New Mexico (USA) Types of Volcanoes

Pyroclastic material is another name for a cloud of ash, lava fragments carried through the air, and vapor. Such a flow is usually *very* hot, and moves *rapidly* due to buoyancy provided by the vapors. Pyroclastic flows can extend miles from the volcano, and devastate life and property within their paths. Damage from pyroclastic flows can occur by impact of rock fragments moving at high speeds or burial of the surface with ash and coarser debris a foot or more thick. Hot pyroclastic surges may start fires and kill or burn people and animals. The most devastating pyroclastic flow occured during the eruption of Mt. Pelee in 1902.Mt. Pelee

Shield Volcano Forms from quiet watery runny lava flow over large area Gently sloping dome shaped mountains Example: Mauna, Hawaii Shield volcanoes, on the other hand, are predominantly lava-based landforms that have gradual slopes and wide bases, because they release fluid lava slowly. These volcanoes can create huge landforms. Mauna Loa and Mauna Kea on the island of Hawaii (The Big Island) are classic examples: Mauna Kea has a base on the ocean floor more than 200 kilometres (120 miles) wide.Hawaii (The Big Island)

Shield Volcano Forms from quiet watery runny lava flow over large area Gently sloping dome shaped mountains Example: Mauna, Hawaii

Composite Volcano Alternating layers of rock particles and runny lava Violent eruption first then quiet eruption that covers the rock particles Cone shaped mountains Mt. Fugi

Caldera Crater, top of a volcano, that collapses or explodes to form a large pit

Volcanic Activity Volcanic activity is unpredictable In order to indicate reactivity of volcanoes, scientist classify them as either active, dormant, or extinct. Active volcano Erupts continually and periodically An active volcano is a volcano that has had at least one eruption during the past 10,000 years. Dormant Volcano A sleeping volcano Known to have erupted in modern times A dormant volcano is an active volcano that is not erupting, but supposed to erupt again. Extinct Volcano Not known to have erupted in modern times but remain unpredictable An extinct volcano has not had an eruption for at least 10,000 years and is not expected to erupt again in a comparable time scale of the future.