As you explore this page, list the potential threats of each physical process, the reasons why people settle in areas where these threats exist, and the steps that people take to deal with these threats: How Can Physical Processes Affect Settlements?
Most of Earth's volcanoes are found in the Ring of Fire, an area that circles the Pacific Ocean, as shown in this map.
The map of the Ring of Fire above shows that many large urban areas are on or near plate boundaries. As urban areas grow,more people are at risk during earthquakes.
Many earthquakes occur below oceans and can cause devastating tsunamis, or huge surface waves. All coastal settlements in earthquake zones are in danger.
The largest earthquakes don't always cause the most damage and loss of life. The amount of damage depends on whether the area affected is densely populated, the strength of the structures, and the emergency measures in place.
This map shows existing deserts and areas that are at risk of becoming deserts. Over 100 countries are losing their drylands to desertification.
Desertification: the gradual process of turning drylands into desert.
Drylands: areas that have semi-desert to moist climates and long growing seasons. These areas make up 41 percent of Earth's land area.
Drought worsens desertification because it directly affects soil quality. Long-term drought reduces moisture in the soil, causing the soil to become dry and thin. The soil then becomes loose and blows away, changing to area into desert.
Desertification is widespread and affects hundreds of millions of people worldwide. The loss of arable land in an area can change settlement patterns there. Long-term drought is threatening food production in Africa's Sahel region. This problem is so severe that people are leaving their homes.
THE GREAT GREEN WALL PROJECT
Long-term drought has caused China's large deserts--the Taklamakan and Gobi deserts--to expand. Over 400 million people are now at risk.
To slow desertification, the government has planted shrubs, grasses, and trees along the edges of the deserts. These plantings are called shelterbelts, and they prevent soil erosion. This project has slowed the desertification rate by about 40 percent since the 1990s.
DUST STORMS
Dust storms are a consequence of desertification. They're common in the Sahara Desert in Africa and in the deserts in China. The dust raised can blow up to 8 km high, adding dust to the atmosphere. This wind can damage equipment and buildings, as well as damage human skin and eyes, and even cause breathing problems.
Dust storms can also have a positive impact. Winds can drop the dust thousands of kilometers from where it was picked up. The soils in Central and South American rainforests get most of their mineral nutrients from dust that came from the Sahara Desert in Africa.
When there's too much water on a slope, the land can slide or flow down the slope, creating a landslide or a mudslide. Settlements near steep slopes covered by clay, sand, or silt are in the most danger. Landslides can result from natural causes, such as heavy rains, melting snow, and earthquakes.
Human activities can also cause landslides. Tree roots help to keep the land in place on slopes; clearing away too many trees makes the land unstable. Also, when roads are built on slopes, the supporting land is sometimes removed which can make the earth unstable. During rainy seasons, the heavy rain and lack of supporting land can cause a landslide.