For example, sedimentary rock shale becomes slate when heat and pressure are added. The more heat and pressure you add, the further the rock metamorphoses until it becomes gneiss. If it is heated further, the rock will melt completely and reform as an igneous rock. Empower your students to learn about the rock cycle with this collection of resources.
Erosion is the process where rocks are broken down by natural forces such as wind or water. There are two main types of erosion: chemical and physical. In physical erosion, the rock breaks down but its chemical composition remains the same, such as during a landslide or bioerosion, when plants take root and crack rocks. Explore the process of erosion with this collection of resources. Weathering is the process of the weakening and breakdown of rocks, metals, and manmade objects.
There are two main types of weathering: chemical and physical. An example of chemical weathering is acid rain. Caused mostly by the burning of fossil fuels, acid rain is a form of precipitation with high levels of sulfuric acid, which can cause erosion in the materials in which it comes in contact. An example of physical weathering is wind blowing across the desert playas. This process causes rocks to form a specific pyramid-like shape and they are called ventifacts.
Select from these resources to teach about the process of weathering in your classroom. Erosion is the geological process in which earthen materials are worn away and transported by natural forces such as wind or water.
A river is a large, natural stream of flowing water. Rivers are found on every continent and on nearly every kind of land. A floodplain is a generally flat area of land next to a river or stream. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Twitter Facebook Pinterest Google Classroom.
Encyclopedic Entry Vocabulary. The Yangtze River flows through the Three Gorges area. Cave entrances can be on land or in water. Corps of Discovery.
Ice Age. Lewis and Clark Expedition. Louisiana Purchase. Olduvai Gorge. Three Gorges Dam. Also called a cascade. What is the difference between a gorge and a ravine? And how does canyon fit in? My impression was that there was an implied scale, where a ravine is smaller than a gorge, which is smaller than a canyon. All of these geographical features seem to be created in the same way: a river or stream eroding hard rocky material, giving steep sides.
Looking at Wikipedia, there are entries for both "ravine" and "canyon". It seems to imply that all three words can be used interchangeably. But are there some technical differences between these words to inform their usage? The definition of canyon from Cambridge seems to fit the best, considering the large size of the Grand Canyon, or Fish River Canyon.
Merriam-Webster seems to agree that a ravine is smaller than a canyon, and also seems to define gorge as a smaller canyon. Overall, given these definitions, I would use canyon for the largest land-forms, and gully for the smallest ones.
Gorge and ravine seem like they could be used interchangeably. Words aren't computer programs. They aren't exactly specified. There's a lot of room for slight differences. Pebble, stone, rock. Honesty, integrity, fidelity.
Kingly, royal, regal. Definitions of words are not the words themselves. They are attempts at capturing how to use words, but you can't, as you can in math, replace a word with its definition and have everything work out as intended. Lexicographers are highly knowledgeable about the nuances of words, but they are constrained by page space or nowadays by reader attention to limit the number of words in a definition. Also, 'canyon' is a borrowing from Spanish into English and is common in the southwest US like 'arroyo'.
All that said, I share your vague perception that a canyon is bigger than a gorge which is bigger than a ravine which is bigger than a gulley. I feel like a river goes through a canyon, a small river or stream through a gorge, a creek or brook through a ravine, and a gulley is often barely a stream to dry.
This may lead to things being called one thing in a gazette but called by scientists one of the others. There are online glossaries or geomorphology. This begins at the table land level and continues downwards. Hard rock is resistant to this weathering process, thus remains on the escarpments in form of granite and sandstones. Gorges form via three forms of natural forces: erosion, geological uplift and glaciers melting. Erosion and washing away of the sediments caused by rivers and streams in valleys is responsible for formation of most gorges in the world.
The Talari Gorges in Mali were formed in this manner. In most cases, geologic uplift works hand in hand with erosion.
These two forces led to the formation of Macocha Gorge in Czech Republic. The Colombia River Gorge in Washington was formed via melting of glaciers, which is the third force that leads to gorges creation. They also provide education regarding changes in land forms in their tales of modes of formation. Some of these landforms are important archaeological sites documenting early human life by way of remains of ancient plants and animal remains.
An example is the Olduvai Gorge cited by the Leakey family as famous for ancient tools and fossils.
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