Quick Review…….. What are the three main sections the earth is divided into? The ________________ is the rigid crust and uppermost portion of the mantle, and it floats on the ______________. The theory that earth’s lithosphere is broken into plates that float on the asthenosphere. Two big evidences for the Theory of Plate Tectonics..… Locations of ____________ and ______________ Three types of plate boundaries…..

Any opening in the Earth’s crust through which molten rock, gases, and ash erupt. vent - the central feature of a volcano. magma - reservoir of molten rock. lava – magma that has reached the surface.

Caldera - large crater-shaped basin formed by the collapse of the top of a composite volcano after an explosive eruption. i.e. Crater Lake (forming from the eruption and collapse of Mt. Mazama)

Volcanology - the study of volcanoes volcanologists - scientists who study volcanoes

3 MAIN TYPES OF VOLCANOES:

volcanoes which consist primarily of erupted volcanic ash and rock fragments, or cinders. i.e. Paricutin, Mexico

volcanoes which pour out large quantities of highly fluid lava in rather mild eruptions and produce a broad, gently sloping volcano. i.e. Mauna Loa, Hawaii Medicine Lake, CA

a combination of both cinder-cone and shield volcanoes. Produces symmetrical, wide-based mountains that consist of alternating layers of lava and cinders. i.e. Mt. Shasta, Mount St. Helens, Mt. Ranier

Which type of volcano is bigger?

3 Classifications of Volcanoes active - a volcano which has erupted within the past few hundred years dormant - a volcano which has erupted many years ago and is now inactive. extinct - a volcano that will “probably” not erupt again. active extinct dormant

WHERE DO MOST VOLCANOES OCCUR? Ring of Fire - the most important volcano belt, a narrow zone of active volcanoes that nearly encircles the Pacific Ocean. Include: Cascade Range, Mt. Fuji, Paricutin, the Aleutian Islands of Alaska

Hot Spots - relatively small, long-lasting, and exceptionally hot regions existing below the plates that provide localized sources of high heat energy to sustain volcanism.

Warning Signs of a Volcanic Eruption bulging or swelling of the slopes minor earthquakes ash plumes & gas emissions

Two Factors that Affect the Violence of a Volcanic Eruption 1)viscosity - “thickness” of the magma. High viscosity - very thick, will plug the vent and allow pressure to build Low viscosity - very thin, oozes out of the cone easily 2)amount of dissolved gas in the magma - if the pressure builds up the gas can’t escape The more gas - the bigger the blast!!!

Types of Volcanic Ejecta Gaseous ejecta water vapor70% other gases - CO 2, N, CO, HCl, SO 2 Liquid ejecta 3 Main Types….. Lake Nyos

pahoehoe - smooth or ropy lava. high temperature flows quickly

aa - rough, jagged lava with a crumbly texture. cooler temperature moves slowly

aa lava pahoehoe lava

pillow lava - smooth pillow- shaped lava which solidifies underwater and cools very fast.

Solid ejecta (pyroclasts) - particles or blocks of solid volcanic ejecta. i.e. volcanic ash, lapilli, cinders, blocks or bombs

nuée ardente - “glowing cloud” – a pyroclastic flow consisting of an incandescent cloud of gas and ash; temperatures up to 2,000°F. ie. Mount Pelée on the island of Martinique (destroyed the city of St. Pierre - 30,000 people) Lahar - Fast moving mudflow caused by the mixture of hot ash with snow & ice on the mountain. i.e. Mount St. Helens Pyroclastic Flow - a dense, superheated cloud of hot, dry rock fragments that travels downhill with amazing speed. i.e. Mt Pinatubo

Lahar

Pyroclastic Flow

nuée ardente

Note: Not all magma makes it to the surface. When magma cools beneath the surface it may form the following structures: laccolith – magma that collects below rock layers and bulges upward. dike – vertical sheet of magma cutting across rock layers. sill - horizontal sheet of magma squeezed between two rock layers. batholith - big laccolith

Dike Sill