Unit E Lesson E5
Completion requirements
Lesson E5: Water Erosion
Video Lesson
How does water shape landscapes? Watch this video to learn more about water erosion.
Lesson E5: Water Erosion
Figure E.2.5.1 β Excess river water causes flooding.
Figure E.2.5.2 β Overflowing rivers erode surrounding riverbanks.
Figure E.2.5.3 β Flooding causes damage to buildings and roads, like these in Bragg Creek.
Reading
and Materials for This Lesson
Science in Action 8
Reading: Pages 352, 355β360
Materials:
Deep baking pan (9 x 13 inches), sand, water, short ruler (15 cm).
Floods
Floods happen when excess water collects in rivers. Sometimes spring flooding happens in Alberta. As mountain snow melts, water collects in small streams and flows downhill. These streams merge into larger rivers, which can overflow from the extra water. If heavy spring rain storms coincide with a large spring snowmelt, flooding can be severe.
The combination of heavy rains and snowmelt caused the June 2013 floods in southern Alberta. Extreme volumes of water flowed down from the mountains into prairie towns and cities. The force of flood waters caused riverbanks to erode, and damaged homes beside rivers. After this flood, several Alberta communities built large rock riverbanks to help prevent flood erosion in the future.
Flash flooding sometimes happens after a heavy rainstorm. Water suddenly collects and flows downhill into low lying areas, eroding land in the process. It is dangerous for people to be caught in a flash flood as water quickly rises. You should always stay out of riverbeds and canyons when it rains heavily.
Floods happen when excess water collects in rivers. Sometimes spring flooding happens in Alberta. As mountain snow melts, water collects in small streams and flows downhill. These streams merge into larger rivers, which can overflow from the extra water. If heavy spring rain storms coincide with a large spring snowmelt, flooding can be severe.
The combination of heavy rains and snowmelt caused the June 2013 floods in southern Alberta. Extreme volumes of water flowed down from the mountains into prairie towns and cities. The force of flood waters caused riverbanks to erode, and damaged homes beside rivers. After this flood, several Alberta communities built large rock riverbanks to help prevent flood erosion in the future.
Flash flooding sometimes happens after a heavy rainstorm. Water suddenly collects and flows downhill into low lying areas, eroding land in the process. It is dangerous for people to be caught in a flash flood as water quickly rises. You should always stay out of riverbeds and canyons when it rains heavily.
Watch More
Flash Flooding
Watch this video to learn more about erosion caused by flash flooding.
Watch this video to learn more about erosion caused by flash flooding.
Figure E.2.5.4 β Meandering rivers have a curved shape.
Figure E.2.5.5 β An oxbow lake forms when river meanders touch.
Eroded River Shapes
Rivers rarely flow in straight lines because erosion shapes rivers into interesting paths.
On flat land, rivers erode curves called meanders. Over time, a river can become so curvy that the two ends of a meander touch. The river will then take a shortcut through the connection point of the meander. The isolated curvy meander is left behind as an oxbow lake.
As a river flows downhill for hundreds of kilometers, it erodes rock and soil. Fast-flowing rivers carry eroded particles, or sediments, downstream. A river slows down as it approaches the ocean. The slower water motion causes sediments to stop and settle near the river mouth. Over time, sediment deposits build up and form islands. The river usually splits into smaller channels that flow around these islands, forming a triangle of connected waterways and land. The fan-shaped formation of channels and islands at a river mouth is called a delta. The name of this shape comes from the Greek letter Ξ, also known as delta.
The Fraser River empties into the ocean south of Vancouver, British Columbia. Here, the Fraser River forms a delta with multiple branches. The city of Richmond is build on a large sediment deposit island between two branches of the Fraser River delta.
Rivers rarely flow in straight lines because erosion shapes rivers into interesting paths.
On flat land, rivers erode curves called meanders. Over time, a river can become so curvy that the two ends of a meander touch. The river will then take a shortcut through the connection point of the meander. The isolated curvy meander is left behind as an oxbow lake.
As a river flows downhill for hundreds of kilometers, it erodes rock and soil. Fast-flowing rivers carry eroded particles, or sediments, downstream. A river slows down as it approaches the ocean. The slower water motion causes sediments to stop and settle near the river mouth. Over time, sediment deposits build up and form islands. The river usually splits into smaller channels that flow around these islands, forming a triangle of connected waterways and land. The fan-shaped formation of channels and islands at a river mouth is called a delta. The name of this shape comes from the Greek letter Ξ, also known as delta.
The Fraser River empties into the ocean south of Vancouver, British Columbia. Here, the Fraser River forms a delta with multiple branches. The city of Richmond is build on a large sediment deposit island between two branches of the Fraser River delta.
Figure E.2.5.6 β When large rivers meet the ocean, they split into deltas.
Figure E.2.5.7 β The Fraser River delta includes the city of Richmond and the Vancouver (YVR) airport.
Watch More
Oxbow Lakes and Deltas
Watch this video for a visual explanation of why rivers meander and how oxbow lakes form.
Watch this video for a visual explanation of why rivers meander and how oxbow lakes form.
This video explains why rivers have deltas.
Figure E.2.5.8 β Johnston Canyon is located in Banff National Park.
Figure E.2.5.9 β Red Rock Canyon is located in Waterton National Park.
Figure E.2.5.10 β Many Alberta canyons have been the sites of amazing dinosaur discoveries.
A canyon is a deep valley with high cliffs on either side. Rivers erode rock into canyons. As a river flows over the same spot for a long time, sometimes for millions of years, the water erodes the underlying rock. A canyon starts as a river with short riverbanks. It eventually gets deeper and deeper, wearing away rock to form high cliffs.
Alberta has some spectacular canyons in its mountain national parks, such as Johnston Canyon, Maligne Canyon, and Red Rock Canyon. Canyons like Horseshoe and Horse Thief Canyons, near Drumheller, have been the site of amazing dinosaur discoveries. One of the most famous and largest canyons in the world is the 1.6 km deep Grand Canyon, in the United States.
Figure E.2.5.11 β Maligne Canyon is located in Jasper National Park.
Figure E.2.5.12 β The Grand Canyon is located in Arizona, USA.
Watch More
Grand Canyon
This video explains how the Grand Canyon formed.
This video explains how the Grand Canyon formed.
Figure E.2.5.13 β When waves erode cliffs, sea arches form.
Figure E.2.5.14 β Collapsing sea arches form sea stacks.
Shoreline Erosion of Crashing Waves
Ocean waves constantly crash against shorelines. The pounding force of the water erodes shoreline rocks, creating coastal landscapes. Often erosion happens gradually, but it can also occur quickly, after strong storms.
Waves erode hard rock into steep cliffs, and then knock down those same steep cliffs. Waves crash against the bottom of a cliff, hollowing out its foundation. When the base of the cliff is too weak to support upper rock layers, the cliff collapses into the ocean. Erosion makes it risky to build homes right on the edge of a cliff.
Curved coastlines are formed by coastal erosion. Waves erode softer rocks quickly, hollowing out round bays on coastlines. The erosion sediments are deposited as sand. Hard rocks erode slowly and extend into the sea, forming headlands.
Wave erosion of headlands creates interesting rock formations like arches and sea stacks. If water erodes a hole into the bottom of a headland, an arch forms. Over time, an arch hole gets bigger and bigger until it erodes completely, leaving a sea stack in the ocean.
Ocean waves constantly crash against shorelines. The pounding force of the water erodes shoreline rocks, creating coastal landscapes. Often erosion happens gradually, but it can also occur quickly, after strong storms.
Waves erode hard rock into steep cliffs, and then knock down those same steep cliffs. Waves crash against the bottom of a cliff, hollowing out its foundation. When the base of the cliff is too weak to support upper rock layers, the cliff collapses into the ocean. Erosion makes it risky to build homes right on the edge of a cliff.
Curved coastlines are formed by coastal erosion. Waves erode softer rocks quickly, hollowing out round bays on coastlines. The erosion sediments are deposited as sand. Hard rocks erode slowly and extend into the sea, forming headlands.
Wave erosion of headlands creates interesting rock formations like arches and sea stacks. If water erodes a hole into the bottom of a headland, an arch forms. Over time, an arch hole gets bigger and bigger until it erodes completely, leaving a sea stack in the ocean.
Figure E.2.5.15 β The ocean erodes cliffs.
Figure E.2.5.16 β Soft rock erodes into a sandy bay, while hard rock extends into the sea as a headland.
Watch More
Coastal Erosion
Watch this video to learn more about coastal erosion.
Watch this video to learn more about coastal erosion.
Coastal erosion can cause cliffs to collapse. Watch this video of coastal erosion in California.
Try It!
Coastal Erosion
Try this simple experiment to observe how ocean waves cause erosion.
Materials:
Try this simple experiment to observe how ocean waves cause erosion.
Materials:
- Deep baking pan (9 x 13 inches)
- Sand
- Water
- Short ruler (15 cm long)
Instructions:
- Pour sand into a short end of the baking pan. Add some water to moisten the sand.
- Form the sand into a rectangular pile that extends about 10 cm into the pan length. The sand pile should reach the height of the baking pan.
- Slowly add water to the other short end of the baking pan. Add water to a height of approximately 2.5 cm.
- Place the ruler into the water end of the pan, opposite to the sand. Use the flat side of the ruler to push water towards the sand, generating waves.
- Push water with the ruler 15 times and observe the sand.
Questions:
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
The force of the water eroded the sand pile. The sand pileβs height dropped, and sand sediments spread out into the water.
You would not see erosion of the hard rock. It takes a very long time for waves to erode hard rock, compared to soft rock or sediments.
The sandstone rock would erode faster. Sandstone is made from layers of sand sediments that can break apart quickly. The granite rock would erode slower. Granite is made from cooled magma which does not contain sediment layers.
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.
Unit E Lesson 5 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps β if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
- DOWNLOAD the self-check quiz by clicking here.
- ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
- COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
-
REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
- SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
- CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Be a Self-Check
Superhero!
Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet β STOP β and go back to step 1 above. Do not look at the answers without first trying the questions.
After a storm, a high volume of rainwater quickly flows downhill. The force of this water can quickly erode rock and soil, causing a landslide.
Retaining walls prevent erosion. Retaining walls create artificial riverbanks that help the riverβs course stay in place instead of eroding additional land in the town. Retaining walls can also raise the height of riverbanks to help prevent
flooding.
High in the mountains, the force of gravity makes water quickly flow down steep slopes. Water flows downhill in the fastest possible straight path without meandering.
Tree roots help hold soil in place. This prevents soil from washing downhill when it rains or snows. Trees also take water out of the ground through their roots, so the soil does not become saturated and susceptible to frequent erosion.
Sedimentary rock is made from layers of sediments. The sediments in the rock are eroded by the force of water to form deep canyon valleys over time. Igneous and metamorphic rock do not contain sediments, which makes them erode slower and less
deep compared to sedimentary rock.