Ch 5 GEY 111-002 MA

Pahoehoe

flow forms a smooth, billowy surface.

Lava tubes

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

Block lava

forms a rough surface of smooth-sided fragments.

Aa flow

forms a rough, broken surface.

Pillow lava

forms a solid, bubble-like mass.

Felsic magmas

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.

Mafic magmas

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

Block

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

Bomb

the largest bombs smoother particles erupted as liquids

What geologic process is related to caldera formation?

volcanism

Lapilli

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

Pumice

lighter vesicular rocks

Cinder 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.

Shield Volcano

-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.

Which of the following are types of volcanoes?

-Composite volcano -Cinder cone -Shield volcano

Which of the following best describe how flood basalts form?

-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.

If previous eruptions had left Mount St. Helens with a different shape, what differences might have influenced the timing of the eruption?

-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.

Volcano Shapes

-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.

What are composite volcanoes made of?

-Pyroclastic deposits -Basalt flows

Which of the following pieces of evidence for a past volcanic eruption are present at Yellowstone National Park?

-Pyroclastic material -A caldera rim -Lava flows

Which of the following features at Yellowstone National Park is evidence for a magma chamber beneath the park?

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

Why are shield volcanoes wider than composite volcanoes?

-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.

Scoria

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

Composite Volcano

-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.

From where do scientists think that mantle plumes originate?

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

Ranking magmas

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

How much material was removed from the volcano?

2.8 cubic kilometers of rock

What is the range of shield volcano height?

300 to 10,000 meters

What is the range of dome complex height?

500 to 2,000 meters

Which of these most directly triggered the main eruption?

A massive landslide

Intermediate 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.

Yellowstone is best described as which of the following?

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.

What are shield volcanoes generally made of?

Basalt flows

How do calderas form?

Calderas form when the summit of a volcano collapses.

What type of volcano is Mount St. Helens?

Composite

bimodal volcanism

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

Which of the following was a stage in the formation of Yellowstone caldera?

Crust bows upward above a magma chamber.

What type of magma erupts out of dome complexes?

Felsic magma

Below is an image of the island of Hawaii. Kilauea, located on the Big Island, is a currently erupting volcano. Which of the following islands is the oldest?

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

Imagine you are a geologist charged with the task of choosing which sites listed below should get state-of-the-art volcano monitoring systems. Which of the volcanoes below is least in need of monitoring?

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.

Pyroclastic rocks

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

Hot spots are best described as which of the following?

Localized areas of volcanic activity not associated with plate boundaries.

In general, how often do most cinder cones erupt?

Most cinder cones erupt once.

There had been many earthquakes in the area prior to this eruption. Why did this last earthquake trigger a massive landslide?

Moving magma had over-steepened the mountain slopes.

Which of the following volcanoes is associated with the Ring of Fire?

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

Where is Crater Lake?

Oregon

What information do geologists use to classify volcanoes?

Shape and type of deposits

What type of volcanoes are the highest?

Shield volcanoes

Basaltic lavas

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.

In addition to rock deposits, what evidence do we have that the eruption that preceded the formation of Crater Lake was very large?

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

Why are shield volcanoes wider than composite volcanoes?

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

Why does Crater Lake have an island in it?

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

Andesitic lavas

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

Rhyolitic lavas

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.

At what tectonic setting is Hawaii located?

oceanic hot spot

What drives melting at divergent boundaries?

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

Cinder cones are made of________.

pyroclastic deposits

Which of the following tectonic settings does NOT produce volcanism?

transform boundary

Ash & Dust

which looks like a fine dust or powder