How do hills change over time

Animals Wild Cities This wild African cat has adapted to life in a big city. Animals This frog mysteriously re-evolved a full set of teeth. Animals Wild Cities Wild parakeets have taken a liking to London.

Animals Wild Cities Morocco has 3 million stray dogs. Meet the people trying to help. Animals Whales eat three times more than previously thought. Environment Planet Possible India bets its energy future on solar—in ways both small and big. Environment As the EU targets emissions cuts, this country has a coal problem. Paid Content How Hong Kong protects its sea sanctuaries. History Magazine These 3,year-old giants watched over the cemeteries of Sardinia.

Science Coronavirus Coverage What families can do now that kids are getting the vaccine. Magazine How one image captures 21 hours of a volcanic eruption. Science Why it's so hard to treat pain in infants.

Science The controversial sale of 'Big John,' the world's largest Triceratops. Science Coronavirus Coverage How antivirals may change the course of the pandemic. Travel A road trip in Burgundy reveals far more than fine wine. Travel My Hometown In L. The Himalayas continue to grow because of faulting activity beneath the Earths surface. Hills are also formed because of erosion , which happens when bits of rock , soil , and sediment get washed away and placed in a pile somewhere else.

Hills can be destroyed by erosion, as material is worn away by wind and water. Hills can also be created by erosion, as material from other areas is deposited near the hill, causing it to grow. A mountain may become a hill if it is worn down by erosion. Parts of the U. However, other parts of the state have a ton of hills. Geologists and geographers have studied the lack of hills in northern Indiana. They discovered that during the Ice Age , glaciers covered the area, mowing down the landscape as they advanced like steamrollers.

The glaciers started to melt once they reached the middle of the state. Running water from the melting glaciers helped form the hilly, rugged landscape of southern Indiana. There are a handful of different types of hills. A drumlin is a long hill formed by the movement of glaciers. A butte is a hill that usually stands alone in a flat area. It has steep sides and a flat top. The rest of the hill was eroded away. A tor is a rock formation on top of a hill.

Sometimes, especially in the United Kingdom, a tor also refers to the hill itself. A puy is a cone-shaped, volcanic hill. A pingo is a mound of ice covered with earth.

These are found in the Arctic and Antarctica. People have used hills for homes and urban areas for thousands of years. Many people have built their homes and villages on hills to avoid floods.

The higher elevation also allows people to defend themselves. Ancient Rome , for example, was built on the city's seven hills so Romans could see their invaders coming from far away. Hill of Ruins In ancient times, when one civilization conquered another the invaders would tear down an old city and just build their new city on top of the ruins. After hundreds of years of such processes, the result was a hill made of layer upon layer of old city debris.

Thousands of these hills, called tels, can be found in the Middle East. Congress works on Capitol Hill. City Upon a Hill The phrase city upon a hill is taken from the Bible, the holy book of the Christian religion. The phrase has come to be associated with the idealism of the United States. John Winthrop, a leader of the early European settlers of Massachusetts, hoped to establish a city upon a hill in Massachusetts in The U.

Congress has two bodies, the House of Representatives and the Senate. The positive side of the molecule attracts negative ions and the negative side attracts positive ions. So water molecules separate the ions from their compounds and surround them. Water can completely dissolve some minerals, such as salt. Follow this link to check out this animation of how water dissolves salt. Hydrolysis is the name of the chemical reaction between a chemical compound and water.

When this reaction takes place, water dissolves ions from the mineral and carries them away. These elements have undergone leaching. Through hydrolysis, a mineral such as potassium feldspar is leached of potassium and changed into a clay mineral. Carbon dioxide CO 2 combines with water as raindrops fall through the atmosphere.

This makes a weak acid, called carbonic acid. Carbonic acid is a very common in nature where it works to dissolve rock. Pollutants, such as sulfur and nitrogen, from fossil fuel burning, create sulfuric and nitric acid.

Sulfuric and nitric acids are the two main components of acid rain, which accelerate chemical weathering figure 7. Acid rain is discussed in the Human Actions and the Atmosphere chapter.

Figure 8. When iron rich minerals oxidize, they produce the familiar red color found in rust. Oxidation is a chemical reaction that takes place when oxygen reacts with another element.

Oxygen is very strongly chemically reactive. The most familiar type of oxidation is when iron reacts with oxygen to create rust figure 8. Minerals that are rich in iron break down as the iron oxidizes and forms new compounds. Iron oxide produces the red color in soils. Now that you know what chemical weathering is, can you think of some other ways chemical weathering might occur?

Chemical weathering can also be contributed to by plants and animals. As plant roots take in soluble ions as nutrients, certain elements are exchanged. Plant roots and bacterial decay use carbon dioxide in the process of respiration.

Weathering rates depend on several factors. These include the composition of the rock and the minerals it contains as well as the climate of a region.

Figure 9. Different rock types weather at different rates. Certain types of rock are very resistant to weathering. Igneous rocks, especially intrusive igneous rocks such as granite, weather slowly because it is hard for water to penetrate them.

Other types of rock, such as limestone, are easily weathered because they dissolve in weak acids. Rocks that resist weathering remain at the surface and form ridges or hills. As the surrounding less resistant rocks were worn away, the resistant center of the volcano remained behind. Different minerals also weather at different rates. Some minerals in a rock might completely dissolve in water but the more resistant minerals remain. When a less resistant mineral dissolves, more resistant mineral grains are released from the rock.

Climate is determined by the temperature of a region plus the amount of precipitation it receives. Climate is weather averaged over a long period of time. Chemical weathering increases as:. So how do different climates influence weathering? A cold, dry climate will produce the lowest rate of weathering.