Ch 5 GEY 111-002 MA

Composite

A massive landslide

Moving magma had over-steepened the mountain slopes.

-If the northern slopes had been less steep initially (same height), the eruption would likely have happened later. -If the volcano had been significantly shorter initially (same steepness), the eruption would likely have happened sooner.

2.8 cubic kilometers of rock

The composition of lavas determine its and flow rate. Basaltic lavas are more fluid due to hotter eruption temperatures and lower silica contents. They produce fast-moving lava flows, flow in sheets, and make up 90% of the lava on Earth.

are less fluid due to cooler temperatures and higher silica contents. The produce slow-moving lava flows and make up 1% of the lava on Earth.

are a type of intermediate lava flow and have properties between those of basaltic and rhyolitic lavas.

forms a rough, broken surface.

flow forms a smooth, billowy surface.

form an outer shell, underneath which lava continues to flow.

forms a rough surface of smooth-sided fragments.

forms a solid, bubble-like mass.

Lapilli, block, bomb, ash & dust, scoria, and pumice

walnut-sized lapilli (particles with sizes of 2-64 millimeters

rougher particles erupted as solids are greater than 64 millimeters (2.5 inches) in size.

the largest bombs smoother particles erupted as liquids

which looks like a fine dust or powder

-Vesicular rocks are characterized by their color, which is derived from composition. -Darker vesicular rocks

lighter vesicular rocks

-Rising (or bowing upward) ground near Yellowstone River -Welded tuff -Geysers and hot springs (steam)

-Pyroclastic material -A caldera rim -Lava flows

An active volcano that has erupted in the last 1 million years. Scientists think that Yellowstone erupted approximately 600,000 years ago and is likely to erupt sometime again.

Crust bows upward above a magma chamber.

volcanism

Calderas form when the summit of a volcano collapses.

Oregon

The eruption was so large that the magma chamber under Crater Lake partially emptied, causing the volcano to become unstable and collapse.

The volcano is still active, and a new volcanic peak has formed.

Continental rift zones were ignored in this exercise because they produce both mafic and felsic magmas

1. most felsic: convergent boundary. 2. medium felsic: convergent. 3. least felsic: oceanic divergent boundary

have a low viscosity and tend to ooze out of the ground rather than erupt violently.

have a high viscosity and tend to erupt violently. Keep in mind, though, that the intensity of a volcanic eruption also depends on the water content of the magma.

A watery intermediate magma with an intermediate viscosity can erupt more violently than a dry felsic magma with high viscosity since the dry felsic magma will not form many bubbles due to its small amount of water.

-Flood basalts form as a result of an eruption above a mantle plume. -Large volumes of basaltic lava are erupted on the surface above mantle plumes, creating thick layers of basalt.

Kaua'i is located furthest away from the current location of the hot spot (the Big Island), so is the oldest.

-shallow locations within the mantle -the outer core-mantle boundary

Localized areas of volcanic activity not associated with plate boundaries.

oceanic hot spot

oceanic hot spot. As the plates move apart, rock from the mantle rises. As the pressure is released, the rock melts.

transform boundary

Mt. Pinatubo is associated with the subduction caused volcanism in the Ring of Fire.

-has a broad and moderately steep flanks and a steep summit. It results from the eruption of a mixture of both lava flows and pyroclastic deposits that contain less fluid materials and travel shorter distances. - Moderately viscous and gas-rich andesitic lavas can erupt as lava flows or pyroclastic materials, leading to the steepening slope of composite volcanoes. -are known for erupting lava and pyroclastic material, and for having a steep summit and moderately broad flanks. -Cotopaxi, Fujuyama, and Mount St. Helens are composite cones.

-A wide volcano that produces mainly basaltic lava flows. -Broad sheets of fluid basaltic lava travel long distances and give shield volcanoes their distinctive shape. -are known for having long lava flows and lava tubes, and for having broad slopes and a caldera. -Mauna Loa is a shield volcano.

-A very steep-sided volcano built primarily from ejected lava fragments. -Explosive eruptions of pyroclastic materials create steep-sided cinder cone volcanoes. -are known for their reddish-brown lapilli, steep sides, and crater at the peak. -San Francisco Peaks and Paricutin are cinder cones.

-Lava composition controls the form and thus the type of volcanoes. This is because the hillslope steepness is affected by different volcano materials -The characteristics of each relate to eruptive style and history. Understanding all of these properties is necessary to understanding the natural hazards that each type of volcano presents.

-The lava that flows out of shield volcanoes is more fluid than the lava that flows out of composite volcanoes. -Geologists classify volcanoes based on their form/structure and also the material erupted. The material erupted determines the shape and spread of the volcano. The figure below illustrates the shape and spread of the five overlapping shield volcanoes making up the Hawaiian Island.

Kauai is no longer an active volcano. The most active island is on the other end of the chain, where the mantle plume is sending magma up to the surface.

-Composite volcano -Cinder cone -Shield volcano

Shape and type of deposits

pyroclastic deposits

Most cinder cones erupt once.

Basalt flows

300 to 10,000 meters

-Pyroclastic deposits -Basalt flows

The lava that flows out of shield volcanoes is more fluid than the lava that flows out of composite volcanoes.

Felsic magma

Shield volcanoes

500 to 2,000 meters