1. Weathering and Erosion
Warmup: How did this boulder come to be in the middle of a road in Malibu?
Learning Concepts: Weathering and erosion. Explain using both weathering (the boulder had to be weathered out of the sandstone) and erosion (the boulder had to slide down the hill).
Caption from New York Times: A 25-foot-high boulder blocked Topanga Canyon Road and cut power lines near Malibu. 1/11/2005. 1

2. What is weathering?
Physical breakdown or chemical decomposition of rock materials exposed at Earth’s surface
Concepts: Weathering
Specifics: Skull Rock in Joshua Tree National Park is from physical weathering of rock. The eye sockets were eroded by water over hundreds of years.
Additional concepts for advanced students: Positive feedback - In the case of Skull Rock, the deeper the weathering, the more water collected, causing yet more weathering.
More info: 2
Photo: Meteorry, Flickr.com

3. Mechanical weathering
sciencemusings.com
Concepts: Mechanical weathering is the process by which rock is broken down into smaller pieces by physical means. Chemical weathering is process by which rock is broken down because of chemical interactions with the environment.
Specifics: In the photo of the tree, al three types of mechanical weathering (ice wedging, abrasion, and organic activity) are occuring. The statue has no face because of acid rain. Emissions from industrial activities mix with rainwater to make it acidific. The acid rain dissolves the mable (calcium carbonate) of the statue.
Chemical weathering 3
futurenostalgia.org

4. Weathering on campus abetteravondalte.org reclusefiles.wordpress.com 4
Concepts: Mechanical vs. Chemical Weathering, continued.
Specifics: Ask students which kind of weathering is occuring in the photos?
Clockwise from left: Cracks in asphalt (mechanical), rusty chain link fence (chemical), crumbling brick with moss (both) 4
reclusefiles.wordpress.com

5. What is erosion?
A process in which the materials of Earth’s surface are loosened, dissolved, or worn away and transported from one place to another by a natural agent, such as wind, water, ice, or gravity
Concepts: Erosion (definition above).
Specifics: The photo is of Torrey Pines State Park (La Jolla, CA), eroded by the mechanical action of water runoff and wave on sandstone. Ask students: where did the rest of the hill go? Why does it have this texture? Why are the sides of the hill so steep?
More info: 5

6. Erosion occurs at different rates
Concepts: Differential weathering and erosion. - erosion and weathering can occur at different rates.
Specifics: The arches in Moab National Park were formed by differential weathering, which means that not all rock wears away at the same rate. This is also an example of slow erosion, since the wind carried the rock that used to be under the arch away.
Erosion can also occur quickly removing a lot of soil at once and washing houses away. This occurs frequently here in Southern California. Ask students if they know of anyone who lives on a cliff or mountain, or if they remember recent incidents of houses sliding down. For example, Mt. Soledad in San Diego CA has experienced significant erosion, damaging houses in 2007.
More info: Photos of Mt Soledad’s damaged houses:
discovermoab.com
Slow
Fast
Army Corps of Engineers

7. Erosion on campus ed brill, flickr.com speedace.info wn.com
Concepts: Weathering and Erosion occur in our neighborhoods and on our campuses.
Specifics: Ask students what they think the photos are, and what happened in them. Tell them that it will help them with their work for tomorrow’s field trip.
Clockwise top left: sidewalk erosion, path erosion, soil erosion.
speedace.info
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8. Conclusion: So what happened to this rock
Conclusion: So what happened to this rock? If students saw this rock on campus, what could they hypothesize about how it got there?
Suggested answer: weathering freed the rock from being stuck in the soil. Erosion then caused it to roll downhill, ending up on a road. 8