Volcanoes Test Review

How many hotspots are on Earth?

100 hotspots

Do you say magma or lava when it comes to silica and viscosity?

Silica- magma in the volcano Viscosity- lava spreads faster/slower when a volcano erupts.

Dormant:

A dormant volcano is one that has not erupted lately but is considered likely to do so in the future.

What are hotspots? Use Hawaiian Islands to explain how they form.

A hot spot is a place where an extraordinary amount of heat rises from the asthenosphere on a plume of magma. The Hawaiian Islands is located on a hotspot on the Pacific plate. Magma on the bottom of the Earth's mantle is heated by the outer core. The magma pushes slowly up to the crust forming a bulge. Under that bulge, some of the rocks melts into magma making its way to the surface of the cracked crust. Making magma become lava. It had a low silica, low viscosity, and low gas.

What is a hotspot? Give an example.

A hotspot is a place where an extraordinary amount of heat rises from the asthenosphere on a plume of magma. An example is the Hawaiian Islands.

Magma Formation

A volcanic eruption occurs when magma (molten rock that has formed deep within Earth) rises to the surface. Conditions at both divergent and convergent boundaries are ideal for magma formation. Most volcanoes are found along mid-ocean ridges and at subduction boundaries. Magma rises to the surface because it has a lower density than the solid materials that surround it. The characteristics of a magma and the rates at which it rises depend upon the amount of silica it contains.

Describe some of the ways that scientists can predict volcanic eruptions.

A volcano that is about to erupt may produce earthquakes. Scientists may use seismographs that record the length/strength of an earthquake to know if a volcano is actually going to happen.

Oceanic crust vs oceanic crust (same for continental vs continental)

A volcano will erupt on which ever crust has less dense because its magma will rise to the crust that has the lower density.

Active:

An active volcano is one that is currently erupting or has erupted recently (in geological terms).

Extinct:

An extinct volcano is one that has not erupted for a very long time and is considered unlikely to do so in the future.

Describe how magma is able to rise through the Earth's crust.

As the boundaries where the plate diverge or converge, the crust becomes weak and fractured allowing the magma to reach the Earth's surface forming a volcano.

Sheild volcano has what type of magma?

Basaltic lava. Because of its low viscosity, basaltic lava tends to flow long distances before hardening.

Describe Basaltic magma in terms of silica and viscosity.

Basaltic magma has 50% (low) silica and a low viscosity. This means that this type oof magma is not super eruptive and spreads was when erupted.

Describe Basaltic magma in terms of silica and viscosity.

Basaltic magma has 50% silica and a low viscosity. This means that this type of magma is not super eruptive and spreads fast when erupted

Describe basaltic, andesitic, and rhyolitic magmas in terms of silica, viscosity, and location.

Basaltic magma has low silica, low viscosity, and low gas. Found at both oceanic crust. Andesitic magma has medium silica, medium viscosity, and medium gas. Found at continental margins forms at subduction boundaries. Rhyolitic magmas have high silica, high viscosity, and high gas. Found at the continental crust. Rhyolitic forms where hotspots are underneath continental plates.

Shield volcanoes

Because of its low viscosity, basaltic lava tends to flow long distances before hardening. In some cases, the lava builds up in layers, forming shield volcanoes with broad bases and gently sloping sides. Shielf volcanoes discharge basaltic lava that is less explosive than other types of volcanoes. Lava flows from shield volcanoes can damage homes, highways, and other property. Generally have quiet eruptions. Example: Kilauea. Location: Hawaii.

Cinder cone volcanoes

Cinder cones, perhaps the simplest type of volcano, forms when molten lava is thrown into the air from a vent. As it falls, the lava breaks into fragment that harden before hitting the ground. Fragment accumulate, forming a cone-shaped mound with an oval base. Cinder cones tend to be smaller than other types of volcanoes, typically forming in groups and on the sides of larger volcanoes. Generally have violent eruptions. Example: Capulin. Location: New Mexico.

Composite Volcanoes

Composite volcanoes develop when layers of materials from successive explosive eruptions accumulate around a vent. The materials include hardened lava flows and other pyroclastic material. After an eruption, a composite volcano may remain relatively quiet for a long period of time. Beneath the surface, gas-rich magma may again be building pressure, eventually leading to another explosive eruption. These types of volcanoes have both explosive and quiet eruptions. Steep sided and symmetrical cone. Example: Mt. Shasta. Location: California.

MOST volcanoes are located at what plate boundary?

Convergent (subduction) plate boundary or subsduction plate boundary.

What is gas? What does gas do to a volcano?

Gas controls how violent the eruptions of a volcano are. It is the reason why a volcano erupts violently or less violently. The higher the gas, the more violent the eruption of a volcano and the lower the gas, the less violence in a volcano.

What is the formation, type of eruption, thick/thin magma & gas content, size, pressure, location, and example for composite cone?

Formed when pyroclastic eruptions (eruptions of ash, cinders, and rock fragments) alternate with lava flows. Violent eruptions but quiet eruptions. Medium gas- Medium viscosity- Medium silica - Thicker magma than shield volcanoes, but thinner magma than cinder cone. Size: steep-sided and symmetrical cones. Medium pressure. Example: Mt. Shasta. Location: California.

What is the formation, type of eruption, thick/thin magma & gas content, size, pressure, location, and example for cinder cone?

Forms when molten lava is thrown into the air from a vent. Violent eruptions. High silica-high viscosity-high gas- thick magma. Size = smaller than other volcanoes. High pressure. Example: Capulin Mountain. Location: New Mexico.

Hawaiian volcano had what type of silica, gas, and viscosity?

Hawaiian had low silica, low gas, and low viscosity

Volcanic Materials- Pyroclastic Flow

In some violent eruptions, pyroclastic material combines with hot gases to form a pyroclastic flow- a dense, superheated cloud that travels downhill with amazing speed. The cloud may follow the course of a valley, moving faster than 100 kilometers per hour. The eruption of mount Vesuvius in A.D. 79 produced a pyroclastic flow that buried the Roman city of Pompeii under pumice and ash.

What is the formation, type of eruption, thick/thin magma & gas content, size, pressure, location, and example for sheild?

Lava builds in layers, forming sheild volcanoes. Less violent eruptions. Low silica-low viscosity-low gas- thin magma. Size: broad bases and gently sloping sides. Low pressure. Example: Kilauea. Location: Hawaii.

Lava Plateaus:

Lava plateaus form as basaltic lava pours out of a fissure (or crack) on the Earth's surface. The basaltic lava that formed the Columbia Plateau in the northwestern U.S. is over one kilometer thick in some places and covers and area of about 164,000 square kilometers.

Shield Volcanoes

Less violent eruptions. Low silica - Low Viscosity - low gas

Volcanoes at Divergent Boundaries

Magma rises through the rift at mid-ocean ridges. While most divergent boundaries are under the ocean, one place where a mid-ocean ridge rises above sea level is Iceland (laki). In 1783 the Icelandic volcano Laki erupted. The eruption killed over ¾ of Iceland's livestock, caused flooding, and destroyed crops, eventually resulting in the deaths of nearly 10,000 people from starvation or disease.

Lahar:

Magma, water, and gases from composite volcanoes explode into a massive cloud of superheated ash and stones. Some of the hot as mixes with snow and ice on the mountain to form fast-moving mudflows called lahar.

Composite Volcanoes in terms of eruption, silica, viscosity and gas

Mildly explosive eruptions. medium silica - medium viscosity - medium gas

Volcanic Materials-Ash ad rock fragments

More explosive eruptions usually involve magmas which contain trapped gasses. When these gases are released, solid fragments called pyroclastic material may be ejected. Pyroclastic materials are classified by size.

The pacific plate is moving what direction?

Northwest. Islands get older as they move to the northwest. The newest island will be located closest to the hotspot.

Over Hot Spots

Not all volcanic activity occurs at plate boundaries. Hot spots are areas of volcanic activity that result from plumes of hot solid material that have risen from deep within Earth's mantle. A hot spot remains in the same place, while the lithospheric plate continues to move across it. The Hawaiian Islands have formed as the Pacific Plate has moved northwest over a hot spot. Today, the youngest island, Hawaii, lies above the hot spot. Island formation continues about 30 kilometers off the coast of the island of Hawaii. Here, an underwater volcano, the Loihi Seamount, is slowly growing into the next Hawaiian Island. Loihi is still about 900 meters below sea level.

What is silica? What does silica do in a volcano?

Silica is a compound. It is a material found in magma that is formed from the elements oxygen and silicon. Silica thickens the magma in a volcano. The lower the silica, the more runny the magma, the higher the silica, the thicker the magma.

Describe Rhyolitic magma in terms of silica and viscosity.

Rhyolitic magma has high silica and a high viscosity. This means that this type of magma is super eruptive, but spreads slowly when erupted.

At what three types of locations do volcanoes form?

River valley, hot spots, and subduction boundary.

How does silica affect magma?

Silica makes magma dangerous bc gases gets trapped in the magma which makes the volcano more explosive.

Info:

Silica is a compound of silicon and oxygen. Silica influences the lava's viscosity and the overall shape of a volcano. Viscosity is the measure of a material's resistance to flow. Gas controls how violent the eruptions of a volcano are. The higher the viscosity in magma the slower the lava will flow and the lower viscosity of the magma, the faster the lava will flow when a volcano erupts. If the magma is spreading slowly, this is because of the high viscosity in the magma which is caused by a lot of silica in the magma. The gas in this particular magma that has low gas will explode less violently. This will give humans more time to escape the hazard. The gas in the magma controls the violence of the lava when erupted by a volcano. Magma can contain high silica and low gas. Magma can also contain high silica and high gas. The gas causes violence in the eruption of a volcano and silica causes the thickness of the lava when the volcano erupts reminding that viscosity is the flowing speed of the lava. There are many types of volcanoes that are organized by their viscosity. For example, Rhyolite lava, with high silica and high viscosity content, has a gentle eruption. Unlike the Rhyolite lava, the Basaltic lava has 50% silica and low viscosity content causing the most damage to humans when the eruption of a volcano occurs. The order of the lowest silica to the highest silica content in volcanoes is Basaltic lava, Andesite lava, Rhyolite lava, and Mantle rocks. Silica is not the only reason why volcanoes are exploding at different speeds. Magma with the higher gas erupts more violently. Magma with the lower gas causes less violent eruptions compared to magma with the higher gas. For example, magma that contains high gas, low silica, and low viscosity results in an explosion of the volcano to be violent, but the lava will be thick so that it will flow slow. Gas, viscosity, and silica determine how the magma or lava in a volcano will react when erupted.

Calderas:

Sometimes magma beneath a volcano is released after the top of the volcano collapses, forming a large crator-shaped basin called caldera. Many active volcanoes have calderas at their summits. In some cases, a caldera fills with water to form a lake - crator lake, oregon. Some calderas are still active (yellowstone N.P).

Info on gas bubbles:

The higher the gas, the less gas bubbles are able to escape causing more violent eruptions

Gas and gas bubbles relationship of a volcano

The higher the gas, the more gas bubble trapped which helps the volcano to erupt more violently. The lower the gas, the fewer gas bubbles are trapped in the magma of a volcano.

Compare silica with viscosity with gas with eruptions

The higher the silica in magma, the thicker the magma, the high the viscosity, the slower the lava flows, the higher the gas, the more violent the eruption of a volcano. The lower the silica, the more runny the magma, the lower the viscosity, the faster the lava flows, the lower the gas, the less violent the eruption will be when a volcano erupts.

What do the lines of volanic islands show?

The lines of volcanic islands show how the lithospheric plates have moved over the hot spots.

Describe the direction of motion of the Pacific Plate over the last 70 million years.

The pacific plate is noving northwest. We know this bc of hotspots. As new lands form as a result of these hotspots, they replace the land that was there before it was causing the old land to shift/move. The direction they move is the direction the plate is moving which in this case is northwest. We know this has changed in the last 40 million years bc there is a bend in the chain of islands that the Hawaiian hotspot has left. This bend illustrates the change in motion of the pacific plate.

Volcanic landforms

The shape and structure of a volcano are determined by the nature of its eruptions and the materials it ejects.

oceanic vs continental crust collision

The volcano will erupt on the continental crust because it has less dense than the oceanic crust.

The Hawaiian islands are different sizes, and have different distances between them. Also, geologists estimate that the current rate of motion of the Pacific Plate is between 8 and 13 cm/yr. What does this tell us about how plates move?

This tells us that the plates move northwest between 8 and 12 cm a year. This proves that the furthir away the plates are from the hotspot, the older the islands are. The closer the plates are to the hotspot, the newer the island is.

cinder cone volcano

Violent eruptions. High silica-high gas-high viscosity

What is viscosity? What is an example?

Viscosity is a meaure of a substance's resistance to flow. Honey is flows slower when poured than water because it has a higher viscosity.

What is viscosity? What does viscosity do in a volcano?

Viscosity is the measure of a material's resistance to flow. Viscosity measures the speed of lava as it flows when a volcano erupts. The higher the viscosity, the slower the lava flows and the lower the viscosity, the faster the lava flows when a volcano erupts.

Volcanoes at Subduction Boundaries

Volcanoes always form on the overriding plate at a subduction boundary. Volcanic mountains form on continental plates (example: the Cascade Range which extends along the Pacific coast from northern California to British Columbia, Canada). Volcanic island arcs form on oceanic plates (example: the Mariana Islands in the Pacific Ocean).

Example of evidence

basaltic lava has 10^4 and the rhyolitic lava has 10^2 viscosity.

Where do volcanoes form?

convergent, divergent, and hotspots

What are 2 plate boundaries that are ideal for magma formation?

divergent and convergent boundaries

Magma that reaches the Earth's surface is referred to as...?

lava

Example of data

motor oil has more viscosity than air

Most volcanoes occur on...?

on the ocean floor not on land or hotpots

what is the major ingrediant in magma?

silica

Most of the volcanoes of the UNITED STATES are located near...?

the Pacific Plate

Name the main gases associated with volcanic eruptions.

water vapor and carbon dioxide