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Science
Chapter 4, part 1
Weathering and Erosion
Agents of change ; stream channels
TOPIC 1:
Physical (mechanical) weathering
Pages 276-280
1. The breaking down of rocks into sediments occurs during a process called
________________________. When this is accomplished through physical force
and does not involve the action of chemicals or chemical change, it is called
______________________ ________________________.
2. Agents of weathering are natural substances or forces that cause weathering to
happen. These include: (list 6)
_______________________, ___________________, ____________________,
_______________________, ___________________, _____________________.
3. When water freezes into ice, it ______________________. This process, called
______________ _____________________ causes mechanical weathering by
splitting rocks apart.
4. When rocks are broken down by the grinding and scraping action of other rocks
or rock sediment, ______________________ occurs. This commonly occurs in
______________________, causing rocks to become rounded and smooth. Sand
and silt carried by ____________________ can create a type of natural
“sandblasting” to rock, forming ventifacts. Also, rocks smash together during a
rock slide as they tumble down a ____________________.
5. The ____________________ of plants and trees may be strong enough to split
them apart as they grow. You have probably seen this effect in sidewalks and
driveways constructed too close to trees.
6. Almost any animal that ______________________ causes mechanical weathering
by breaking up soil and moving around rocks, exposing them to further
weathering. Of course, humans cause a lot of weathering through quarrying,
mining, and construction activities.
TOPIC 2:
Chemical weathering
Pages 281-283
1. The process by which rocks break down as a result of chemical reactions is called
__________________ ______________________ and its common agents are
___________________, _____________________________, and
_______________.
2. In the process of dissolution, ______________________ dissolves some of the
rock’s minerals, causing the rock to disintegrate. Most water is slightly
___________________ due to pollution in the air. This causes chemical reactions
with the rock that cause it to decompose.
3. ____________ _____________________ is when rain or snow is unusually
acidic due to high concentrations of pollutants. This can be harmful to plants and
animals as well as rocks.
4. Acids are also present in much of the _________________________ since it
dissolves gases such as carbon dioxide as it percolates through the soil. This can
result in the chemical weathering of rocks underground, forming karst features
such as ________________________. These features are common in areas with a
moist climate and layers of the rock _____________________ near the surface.
5. Plants that produce acids to slowly break down rocks are called
______________________. They are a moss-like plant that feeds off the minerals
from decomposed rock or bark.
6. Air can be an agent of chemical weathering. During the process of
_____________________, oxygen in the air may chemically react with
_________________ in some rocks. This reaction is sped up by the presence of
___________________.
TOPIC 3:
Differential weathering
Pages 284-287
1. The rate (speed) at which rocks weather depends on ____________________,
________________________, and the _____________________ of the rock.
2. Hard, resistant rocks such as granite and sandstone weather more
__________________ than soft, weak rocks such as limestone and shale. When
two different types of rock in an area weather at different speeds, a process called
_________________________ _________________________ occurs. This
process can result in ledges, hills, waterfalls, and strangely shaped rock outcrops
such as spires, monuments, and volcanic necks and dikes.
3. Weathering occurs more quickly when the rocks are _______________ in size.
This is because they have more surface _______________ to volume exposed to
the weathering processes.
4. Weathering occurs more quickly in ___________________ and
__________________ climates. This is because ____________________
____________________ happen at a faster rate when temperatures are higher and
water is present.
5. Weather occurs more quickly when the land elevation and slope is
_______________________. This is due to an increase in wind, rain, ice, and
movement of water.
Continued on page 2..
TOPIC 4:
Stream erosion
Pages 308-312
1. The Grand Canyon was created by the processes of weathering (breaking down of
rock) and ________________________, which is the movement of broken down
rock and sediment away from its source to a new location. This was accomplished
through the action of the Colorado ___________________.
2. The continuous movement of water through rivers is made possible by the
_______________ _________________, which gets its energy from the
_______________.
3. Rivers collect water over an area of land known as their ____________________.
Within this area, smaller streams called _____________________ collect and
deliver water to the river. River systems are separated from one another by areas
of high ground called a ____________________.
4. As streams erode soil and rock they carve a ____________________, which then
directs the flow of water and forms a path for the river to follow. Over time these
become ___________________ and eventually ___________________ as a result
of continual weathering (by abrasion) and erosion.
5. The rate at which a river weathers and erodes its channel depends on several
factors. One factor is the stream’s _____________________, or drop in elevation
over a certain distance. The greater this factor, the greater the force of gravity
exerted on the water to move it and the faster the stream flows.
6. Another factor is the amount of water moved by the stream through a section of
its channel in a given amount of time, which is called __________________. This
depends both on speed and volume of water. This factor can change daily
depending on the weather.
7. The last factor is the stream’s _________________, or amount and size of
sediment and rock being moved with the stream. The larger the size of the
sediment, the greater the erosive power of the river. This in turn depends on the
_________________ of the current.
8. Larger rock and sediment that is moved by bouncing, rolling, or sliding along the
bottom of the river is called the _________ _________________. This causes the
stream channel to get deeper through weathering by abrasion.
9. Smaller sediments such as silt and clay are light enough to be carried suspended
in the water. These make the river look __________________ but cause relatively
little weathering. Even streams that look clear may carry a
_____________________ load of soluble minerals and chemicals that can make
you sick if you drink them.
TOPIC 5:
Stages of river development
Pages 313-314
1. The stages of a river’s development as identified by William Morris Davis are
used today to describe a river’s general _____________________, not a river’s
actual age. Rivers with narrow, straight, and normally steep-sided channels are
described as ________________________ rivers.
2. Youthful rivers flow __________________ due to a steep gradient. Rapids and
_______________________ are common features of their channel due to
differential weathering of the channel bedrock.
3. As a river matures, its ______________________ decreases, resulting in a slower
current. Their channels become ___________________ rather than deeper due to
meanders that develop in the river’s path. They have _______________ rapids
and waterfalls than a youthful river.
4. Although mature rivers have less speed, they typically have more
_________________ as a result of being fed by many _____________________.
5. An old river has a low _______________________ and little
___________________ energy. The slowing of the water currents results in the
deposition (depositing) of much of its load in and along its channel. This creates
land within the channel called _________________ _____________________
and results in the formation of a wide valley.
6. An old river can act young again if the gradient is raised by
___________________ _____________________ or a drop in sea level. When
this occurs, the river is said to be __________________________. It begins
downcutting deeper once again, forming a flat, step-like platform of land within
the channel called a _________________________.
** application – not in book**
A real river does not have a single “age” or stage of development, but has sections of
all three. Rivers begin forming near the mouth and then over time they grow toward
the headwaters (called “headward erosion”). For this reason, they have old-age
features near the mouth, youthful features near their headwaters, and mature features
in between. Their profiles more closely resemble a slide than a ramp.
TOPIC 6:
River deposits
Pages 316-319
1. Describe the formation of a meander as a result of both erosion and deposition.
2. Describe why and where rivers deposit the material they erode.
3. Identify and describe two features along a river channel formed by river deposits
(including locations). Describe both a benefit and a danger to living in these areas.