Biology Volcanoes Chapter 9
in what way do volcanoes erupt?
explosively or non-explosively
what are explosive erupting volcanoes derived from?
granitic magma
how is continental crust
grantic and rich in silica
what is an extinct volcano?
have not erupted in recorded history, and will not erupt again
what can happen as magma moves upward prior to an eruption
it can cause the side of a volcano to bulge.
what is pyroclastic material?
it forms when magma is blasted into the air and hardens.
Describe Aa lava
it pours out quickly and forms a brittle crust. The crust is torn and jagged into pieces as molten lava continues to flow underneath
what does magma do when a rift zone is created?
it rises to fill the gap
what do explosive eruptions create?
large explosive clouds of ash ( dust- sized particles of molten rock that harden in the air) and gases.
what are the most common types of eruptions?
nonexplosive eruptions
describe pahoehoe lava
pahoehoe lava flows slowly, like wax dripping from a candle. Its glassy surface has rounded wrinkles.
describe pillow lava
pillow lava forms when lava erupts underwater. The lava forms rounded lumps that are in the shape of pillows.
what are convergent boundaries?
places where tectonic plates collide.
what is the ring of fire
plate boundaries surrounding the Pacific Ocean have so many volcanoes that the area is called the Ring of Fire.
what have scientists learned by comparing magma from different eruptions?
scientists have learned that the composition of the magma affects how explosive a volcanic eruption is.
what happens to rock if the temperature of a rock remains constant but the pressure on the rock decreases?
the rock becomes liquid
what is the type of magma that tends to cause explosive eruptions
the magma with high silica and high viscosity.
what happens when an oceanic plate collides with a continental plate
the oceanic plate usually slides underneath the continental plate (subduction)
what are lapilli?
they are small and pebblelike bits of magma that hardened before they hit the ground.
what are volcanic blocks?
volcanic blocks are pieces of solid rock erupted from a volcano. Boulders are largest pieces of pyroclastic material.
what are volcanic bombs?
volcanic bombs are large blobs of magma that harden in the air
what are mid-ocean ridges?
volcanoes and mountain chains created by lava that flows from undersea rift zones
how do volcanic eruptions affect climate?
when enormous amounts of volcanic ash and gases are ejected into the upper atmosphere, they can block enough sunlight to cause global temperature to drop.
when does magma form in the mantle?
when the pressure is low and the temperature is high.
what is the origin of the word Aa?
Aa is named so because of the painful experience of walking barefoot across the jagged surface.
name the 4 types of lava
Aa lava, pillow lava, blocky lava and Pahoehoe.
In addition to volcanoes, what are other landforms produced by volcanic activity?
Lava plateaus, Calderas and Craters
what is a vent?
The vent is an opening at the surface of the Earth through which magma passes.
what is volcanic ash and how does it form?
Volcanic ash forms when the gases in stiff magma expand rapidly and the walls of the gas bubbles explode into tiny, glasslike slivers. Ash makes up most of the pyroclastic material in an eruption.
explain how an explosive eruption happens
While underground, magma is under intense pressure and water in it stays dissolved. If the magma quickly moves to the surface, pressure suddenly decreases and the water and carbon dioxide become gases. As gases expand rapidly, an explosion can result.
where does most of the volcanic activity occur?
at mid-ocean ridges
how is oceanic crust
basaltic and poor in silica
what are quietly erupting volcanoes derived from?
basaltic magma
why does an oceanic plate tend to subduct when it collides with a continental plate
because an oceanic plate is denser.
describe blocky lava
blocky lava is cool, stiff lava that does not travel far from the erupting vent. Blocky lava usually oozes from a volcano and forms jumbled heaps of sharp-edged chunks.
what are the 3 types of volcanoes?
cinder cone volcanoes, shield volcanoes and composite volcanoes
what is an active volcano?
currently erupting, or show signs of erupting in the near future
what is a dormant volcano?
currently not erupting, but may erupt again
What are 2 theories of why a hot spot produces a chain of volcanoes?
1. One theory is that the mantle plume stays in the same spot while the tectonic plates move over it. 2. Other scientists think that hot-spot volcanoes occur in chains because they form along cracks in the Earth's crust.
compare the shapes of cinder cone volcanoes, shield volcanoes and composite volcanoes.
1. Shield volcanoes are wide-based and have gentle slopes 2. cinder cone volcanoes are narrow-based and have steep slopes 3. A composite volcano is wide-based and also steep.
How Do Scientists Predict volcanic Eruptions?
1. they measure small quakes 2. Studying the composition and volume of gases 3. Measuring Slope and Temperature
what is a crater?
A crater is a pit in the shape of a funnel. It is the uppermost part of the volcano and is smaller than the caldera.
what does a hot spot produce?
A hot spot often produces a chain of volcanoes
What is a volcano?
A volcano is a vent or fissure in the Earth's surface through which molten rock and gases are expelled
what happens when the oceanic plate subducts?
As the oceanic tectonic plate subducts, it becomes hotter and releases water vapor, which lowers the melting point of rock in the mantle and forms magma.
how is a rift zone created?
At a divergent boundary, tectonic plates move away from each other, forming a set of deep cracks called a rift zone between the plates.
where is volcanic activity common?
At tectonic plate boundaries, because it is where magma tends to form.
what are calderas?
Calderas are large, semicircular depressions that form when the magma chamber below a volcano partially empties and causes the ground above it to sink. Calderas can appear similar to craters, but are many times larger.
what causes magma to form?
Changes in temperature & pressure cause magma to form.
describe cinder cone volcanoes
Cinder cone volcanoes are made of pyroclastic material produced from moderately explosive eruptions. They have steep slopes. They're small and erupt for a short time; occur in clusters on sides of other volcanoes.
describe composite volcanoes
Composite volcanoes (Stratovolcanoes) are formed from explosive eruptions of pyroclastic material, followed by quieter flows of lava. They have broad bases and sides that get steeper toward the top
what are craters?
Craters are funnel-shaped pits near the top of the central vent of a volcano
what are hot spots
Hot spots are volcanically active places on the Earth's surface that are far from plate boundaries.
what is the newest method of recording changes in surface temperature and gas emissions of a volcano
Infrared satellite images
what are lava plateaus
Lava Plateaus are wide, flat landforms resulting from repeated nonexplosive eruptions of lava that spread over a large area.
how does magma form?
Magma forms in the deeper regions of the Earth's crust and in the uppermost layers of the mantle, where temperature & pressure are high
what is the difference between magma and lava?
Magma is composed of molten rock and stays below the Earth's crust. Lava is magma that does reach the surface of the earth, when it explodes through a volcano's vents.
when forming a volcano, why does magma rise to the surface?
Magma is less dense than the surrounding rock
what would an increase in seismic activity be indicative of?
Magma might be moving in the magma chamber.
what is lava?
Magma that flows onto the Earth's surface.
what substance can cause an explosive eruption?
Magma with a high silica( most abundant mineral in the crust of the Earth) content also tends to cause explosive eruptions.
what are pyroclastic flows?
Pyroclastic flows are dangerous volcanic flows that are produced when enormous amounts of hot ash, dust, and gases are ejected from a volcano.
describe shield volcanoes
Shield volcanoes are built of layers of lava that are released from repeated nonexplosive eruptions. Runny lava spreads out over a wide area creating a volcano with gently sloping sides.
what does silica-rich magma do?
Silica-rich magma has a stiff consistency, so it flows slowly and tends to harden in a volcano's vents and plug it. As more magma pushes up from below, pressure increases. If enough pressure builds up, an explosive eruption takes place.
what are some of scientists' hypothesis about hot spots?
Some scientists think that hot spots are directly above columns of rising magma, called mantle plumes.
how does lava erupt from a lava plateau?
The lava erupts from long cracks, or rifts, in the crust over a period of millions of years
what is a magma chamber?
The magma chamber is the body of molten rock deep underground that feeds a volcano.
what do nonexplosive eruptions create?
They produce relatively calm flows of lava in huge amounts.
what is a caldera?
a caldera is a large semi-circular depression that forms once the magma chamber below a volcano partially empties and causes the ground to sink. It sits on top of the magma chamber.
what is another name for a composite volcano
a stratovolcano
what do scientists use to detect changes in a volcano's slope
a tiltmeter and a GPS
what will make an eruption explosive?
depends upon the silica, water, and gas content of the magma. If the water content of magma is high, an explosive eruption is more likely
What is another name for molten rock?
magma
what does subduction produce
magma
what erupts from a volcano?
magma erupts as either lava or pyroclastic material
Around how many active volcanoes are there on Earth?
more than 500