A ravine is a very narrow and steep crevice in the Earth’s surface. Ravines are smaller than valleys but larger than ravines, although a ravine has the potential to turn into a valley, over thousands of years. Ravines are especially common in urban areas, although they can also be found in other parts of the world, and care should be taken when walking through ravines as the sides can collapse, causing people to fall and injure themselves.
Typically, a ravine is formed through the process of erosion and begins as the site of a small stream or river. Over time, water wears down a deep groove in the Earth, which attracts water as it drains from other locations, accelerating the erosion process. Eventually, a ravine may lose its flow or have only intermittent water flow because it cannot sustain water year-round. Sometimes, however, a ravine will have a year-round watercourse.
Urban areas tend to have more ravines than other locations because urban drainage is often poor, and this promotes ravine formation. It is common for water to accumulate in a large mass in urban areas, creating a rushing torrent, because it cannot naturally seep into the ground to run off. As the water has to go somewhere, it can end up creating a cut in periods of floods and heavy rains, and this will evolve into a ravine.
The ravines have historically been used for garbage disposal, due to their depth and steep slopes. Although this practice is largely discouraged today, the ravines still tend to collect rubbish, which is carried by the water that periodically flows through them, as well as being thrown in by careless litters. In urban areas, service organizations may designate one day each year to clean local ravines, canyons and waterways so that litter does not accumulate for too long.
Depending on the location of a ravine, it can also serve as a habitat for local wildlife, especially in regions where wildlife is under pressure due to human habitation. Humans tend to avoid ravines as they are difficult to navigate, and this allows a variety of creatures to move and live unmolested there. As a result, ravines are sometimes great spots for birding and other wildlife viewing.