Constructive and Destructive Forces Test
Chapter THREE
Section One BIG IDEAS
Test date: December
Volcanoes
Volcanoes and Plate Tectonics
th
Study Guide
1. A volcano is an opening (weak spot) in the Earth’s surface where magma escapes
from the interior. Magma that reaches the Earth’s surface is called lava.
2. The constructive force of volcanoes adds new rock to existing land and forms
new islands.
3. Most volcanoes occur near the boundaries of Earth’s plates and along the edges
of continents, in island arcs, or along mid-ocean ridges.
VOCAB
Volcano – a weak spot in the crust where magma comes to the surface
Magma – the molten mixture of rock-forming substances, gases, and water from the mantle
Lava – Liquid magma that reaches the surface; also the rock formed when lava hardens.
Ring of Fire – a major belt of volcanoes that rims the Pacific Ocean
Section Two BIG IDEAS
Volcanic Activity
1. An eruption occurs when gases trapped in magma rush through an opening at
the Earth’s surface, carrying magma with them. The less dense molten
material moves upward from the mantle.
2. Volcanoes can erupt quietly or explosively, depending on the amount of
dissolved gases in the magma and how thick or runny the magma is based on
the amount of silica in it, and the magma’s temperature
3. When magma heats water underground, hot springs and geysers forms.
4. Volcano hazards include pyroclastic flows, avalanches of mud, damage of
ash, lava flows, flooding, and deadly gases
VOCAB
Magma chamber – the pocket beneath a volcano where magma collects
Pipe – a long tube through which magma moves from the magma chamber to Earth’s
surface
Vent – the opening through which molten rock and gas leave a volcano
Crater – a bowl-shaped area that forms around a volcano’s central opening
Silica – a material that is formed from elements oxygen and silicon; silica is found in
magma
Pyroclastic flow – the expulsion of ash, cinders, bombs, and gases during an explosive
volcanic eruption
Active – said of a volcano that is erupting or has shown signs of erupting in the near
future
Dormant – said of a volcano that does not show signs of erupting in the near future
Extinct – said of a volcano that is unlikely to erupt again
Geyser – a fountain of water and steam that builds up pressure underground and erupts at
regular intervals
Section Three BIG IDEAS
Volcanic Landforms
1. Lava and other volcanic materials on the surface create shield volcanoes, cinder
cones, composite volcanoes, and plateaus.
2. Magma that hardens beneath the surface creates batholiths, dome mountains,
dikes, and sills, which are eventually exposed when the covering rock wears
away.
VOCAB
Shield volcano – a wide, gently sloping mountain made of layers of lava and formed by
quiet eruptions
Cinder cone – a steep, cone-shaped hill or mountain made of volcanic ash, cinders, and
bombs piled up around the volcano’s opening
Composite volcano – a tall, cone-shaped mountain in which layers of lava alternate with
layers of ash and other volcanic materials; most explosive
Caldera – the large hole at the top of the volcano formed when the roof of a volcano’s
magma chamber collapses
Volcanic neck –a deposit of hardened magma in a volcano’s pipe exposed after the
surface erodes away
Chapter Two
Section One BIG IDEAS
Earthquakes
Earth’s Crust in Motion
1. Stresses on Earth’s surface show compression, tension, and shearing on rock.
2. Faults are cracks in Earth’s crust that result from stress.
3. Faulting and folding of the crust cause mountains and other features to form on
the Earth’s surface.
VOCAB
Earthquakes- the shaking that results from the movement of rock beneath Earth’s surface
Fault- a break in Earth’s crust where slabs of rock slip past each other
Strike-slip fault - a type of fault where rocks on either side move past each other
sideways with little up-or-down motion
Normal fault – a type of fault where the hanging wall slides downward; caused by
tension in the crust
Reverse fault –a type of fault where the hanging wall slides upward caused by
compression in the crust
Fault-block Mountain – a mountain that forms where a normal fault uplifts a block of
rock
Fold- a bend in rock that forms where part of Earth’s crust is compressed
Anticline – an upward fold in rock formed by compression of Earth’s crust
Syncline- a downward fold in rock formed by compression in Earth’s crust
Plateau- a large area of flat land, elevated high above sea level
Section Two BIG IDEAS
Measuring Earthquakes
1. As seismic waves travel through Earth, they carry the energy of an earthquake
from the focus to the surface
2. Earthquakes produce two types of waves, P waves and S waves, which travel
out in all directions from the focus of the earthquake.
3. Today, the Moment Magnitude scale is used to determine the magnitude of an
earthquake. Other scales that geologists have used to rate earthquakes include the
Mercalli scale and the Richter scale.
VOCAB
Focus – the point beneath Earth’s surface where rock breaks under stress and causes an
earthquake
Epicenter - the point on Earth’s surface directly above an earthquake’s focus.
Seismic waves- a vibration that travels through Earth carrying the energy released during
an earthquake
P waves – a type of seismic wave that compresses and expands the ground
S waves – a type of seismic wave that moves the ground up and down and side to side
Seismograph – a device that records ground movements caused by seismic waves as
they move through Earth
Richter scale- a scale that rates seismic waves as measured by a particular type of
mechanical seismograph
Moment magnitude scale – a scale that rates earthquakes by estimating the total energy
released by an earthquake
BIG IDEAS Weathering, Erosion, and Deposition
1. There are three types of weathering: biological, mechanical (AKA physical) and
chemical
2. Mechanical weathering is the breaking down of rocks into smaller pieces. The
change in the rock is physical with little or no chemical change. Examples of
mechanical weathering are freezing/thawing, abrasion (wind/water/friction), and
pressure releases (gases given off).
3. Chemical weathering is the decomposition of rock from exposure to water
and/or atmospheric gases (principally carbon dioxide, oxygen, and water vapor).
As rock is decomposed, new chemical compounds form. Examples of chemical
weathering are rusting, acid breakdown from plants, and solution weathering
(copper turns green), acid rain.
4. Biological Weathering is the action of living things on the solid surface of the
Earth. Lichen breaking down rock is one example.
5. Erosion is the picking up or physical removal of rock particles by an agent such
as a stream or glacier. Weathering helps to break down or erode material such as
rock or soil. Most rock particles are partially weathered, but rock can be eroded
before it has weathered at all.
VOCAB
Weathering- the process of breaking down of rocks and other materials on the Earth’s
surface
Erosion – process by which rock, sand, and soil are broken down and carried away
Deposition – process in which sediment is laid down in new locations
LEQ: “How do constructive forces build up Earth’s surface while destructive forces
wear away the Earth’s surface?
Example response: Constructive forces that build up the Earth’s surface such as
volcanoes and deposits of sediment, sand, and ice can create land, sand dunes, and carve
out lakes through glaciers. These forces can help raise the elevation of a land area.
Destructive forces that wear away the Earth’s surface such as weathering and erosion,
earthquakes, tsunamis, as well as flash floods will break down the Earth’s surface in
places. Sometimes events like volcanoes can be both destructive and constructive by the
spreading of new molten material on surfaces. That same volcano can contribute to
erosion by destroying trees and other plants allowing the surface to be torn away.