Volcanoes
Name:
Here we will compare extrusive and intrusive volcanic features and action
q distinguish magma from lava
q identify intrusive and extrusive igneous features (e.g., sill, dike, batholith)
q describe types of eruptions (e.g., cinder cone, composite, shield, basalt plateau, rift), the volcanoes or extrusive
events that produce them, and their effects
Magma vs. Lava
Difference Between Magma and Lava
Not many of us know that the temperature beneath the surface of the earth increases as we descend. In fact, the
temperature at the center or the heart, as it is called, is so high that it consists of nothing but melted rocks and other solid
substances due to extremely high temperatures. We call this mixture of molten rock magma. This magma makes home for
itself in some places called compartments that have a way up to the volcanoes. After the eruption of the volcanoes, it is
this magma that constantly fills volcanoes. When the magma comes from the volcanoes it’s called lava. Although
technically there is no difference between the magma and lava, owing to the fact that magma is actually lava, there are
many who remain troubled by their differences. This article attempts to discover differences, if any such between magma
and lava.
Now that we know that both magma and lava is molten rock, the differentiation between the two must be related to their
different locations. We stand on the coolest surface of earth and can not even think or imagine how hot it is in the center
of the earth. As you travel down into the crust and the mantle, the temperature increases gradually and there are pockets
where you can find cape molten rock. This molten rock, called magma finds its way to the surface of the earth through
cracks and also compartments that are introduced into the volcanoes.
The earth’s crust consists of plates that continue to run onto each other. Normally these plates fit together like pieces of a
huge puzzle, but when they move, they cause friction and release a lot of energy. When the plates collide, they slide over
one another and the one that is most underneath is pushed further down. This causes the molten rock or magma to make
its way up between the plates.
For those who think of volcanoes as the fury of nature, they are in fact giant safety valves that release the pressure that
builds up due to high temperatures inside the earth. The temperature of the magma, reaching the volcano mouth is about
700-1300 degrees Celsius. When this Magma comes from a volcano, it is known as the lava. There are different types of
lava, which are classified according to their consistency or viscosity. The lava is of thin density and flowing may stream for
miles and flowing gently in a slope. Due to being thick, it is very difficult for the lava to flow and gather around the mouth
of the volcano. The thickest and most dense lava doesn’t flow all. It blocks the mouth of a volcano, causing larger
explosions in the future.
Magma vs. Lava
Magma = ______________________ the surface of the earth
Lava = magma that has reached the __________________________
Intrusive and Extrusive Igneous Features
1. _____________________features = parts of volcanic activity found _________________________________________
__________________ = Intrusive igneous rocks of any size. Formed ______________________________.
Types of ___________________
a) ____________________________________
(Big: >100 km2) = a body of igneous rock formed
beneath the Earth’s surface by the intrusion and
solidification of magma.
b) __________________ (Smaller than batholith: <10 km2)
c) __________________= a sheet of rock that formed in
a crack in a pre-existing rock body that cuts across
layers in a planar wall rock structures.
However, when the crack is between the layers in a
layered rock, it is called a sill, not a dike.
Castle Crags stock,
Klamath Mtns,
Dunsmuir, CA
A diabase dike
crosscutting
horizontal lime
stone beds in
Arizona.
Magmatic dikes radiating from West Spanish
Peak, Colorado, USA
d) __________________ = a sheet of rock that formed__________________________in a pre-existing rock body.
2. __________________features = parts found __________________the volcano
a) Magma (lava)
Overall, the behaviour of the magma determines the
type of volcano that develops:
Main types of magma
i) Mafic (basaltic) Magmas:
o __________________ (900-1200oC)
o very low __________________ (very
fluid)- __________________
o No presence of __________________ (ie., not quartz)
o Contain mafic minerals (olivine, pyroxene)
Low SiO2 magmas, with ____________________________________, flows readily through their vents and
across the land surface when the lava escapes the vents.
ii) Silicic/Felsic Magmas
o __________________ (~650-900oC)
o __________________- slow flowing
o ~65-77% __________________contain felsic minerals (quartz, feldspar)
High SiO2 magmas, __________________and with __________________, tend to __________________ their
vents until the force of escaping magma blows the vent clear; such magmas cause __________________
volcanoes.
Viscosity = ____________________________________
o Viscosity depends on temperature and composition (if SiO2 is present, lava flows slower)
Lava Deposits
__________________: A tube formed by cooling and solidifying of the lava walls
while fluid lava continued to ____________________________________.
__________________: A form of closed lava tube (with a bulbous end) that
forms when lava flows __________________ (e.g., a lake or ocean) and cools
very rapidly.
b) __________________material = Debris formed by a volcanic explosion. Results when magma is
____________________________________.
__________________= The general term for all pyroclastic material that is ejected from a volcano. Different terms
apply according to the size of the tephra. (syn. Ejecta)
Types of Material
a) __________________: tephra that is finer than 2 mm in
diameter.
b) Lapilli: from 2 mm to 64 mm in diameter.
c) __________________:
hard fragments greater than 64
mm in diameter.
d)
__________________: formed when a volcano ejects viscous fragments of lava during an eruption. They
cool into __________________________before they reach the ground.
http://en.wikipedia.org/wiki/Volcanic_bomb
e) __________________: A deposit made up of ash.
f)
__________________: A water saturated slurry of ash and other volcanic debris that flows downslope.