A collection of questions and answers addressing Earth Science topics by the United States Geological Survey. 

1. What is the age of Planet Earth?

Earth is over 4 1/2 billion years old.

 

2. At what rate is the San Andreas fault moving in California?

The San Andreas fault is slipping at a rate of approximately 2 inches per year causing Los Angeles to move towards San Francisco. Scientists project that Los Angeles will be a suburb of San Francisco in approximately 15 million years.

 

3. What is the largest volcano in our solar system?

Olympus Mons on Mars is the largest volcano yet found in our solar system. It is nearly 400 miles wide and rises 16 miles into the thin Martian atmosphere. The base of Olympus Mons would almost cover the entire State of Arizona.

 

4. What is the largest volcano on Earth?

Mauna Loa volcano in Hawaii is the largest volcano on Earth, both in terms of volume and height above its base. Mauna Loa consists of about 19,000 cubic miles of lava and rises more than 50,000 feet above its base. Because of its massive size, the volcano has depressed the ocean floor about 5 miles.

 

5. Do earthquakes occur in the central portion of the United States?

Yes, some of the most powerful earthquakes in United States history occurred along the New Madrid fault in the Mississippi Valley in 1811-1812. The effects of shaking from these magnitude 8+ earthquakes caused church bells to ring in Boston, Massachusetts nearly, 1,000 miles away.

 

6. At what depth do most earthquakes occur?

Most earthquakes occur at depths of less than 50 miles from the Earth’s surface.

 

7. Where do some of the deepest earthquakes occur?

The deepest earthquakes typically occur at plate boundaries where the Earth’s crust is being subducted into the Earth’s mantle. These occur as deep as 400 miles below the surface.

 

8. Where are the oldest rocks on Earth found: on land or on the ocean floor?

On land. Since the ocean floor is being continually regenerated as the continental plates move across the Earth’s surface, the oldest rocks on the ocean floor are less than 300 million years. In contrast, the oldest continental rocks are 4,500 million years old.

 

9. Are the rock formations in the Grand Canyon older at the top or bottom of the canyon?

At the bottom. On average, the rocks at the bottom of the canyon are 570 million years old, whereas those near the top are 245 million years old. However, some crystalline rocks at the bottom are nearly 1.8 billion years old.

 

10. What is the largest canyon found in our solar system?

Valles Marineris, on the planet Mars. This huge canyon extends for about 3,000 miles. If placed on the United States, Valles Marineris would stretch from New York City, New York, to Los Angeles, California, and is much deeper than the Grand Canyon.

 

11. Where and when did the deadliest recorded earthquake occur?

The world’s deadliest recorded earthquake occurred in 1557 in central China.It struck a region where most people lived in caves carved from soft rock. These dwellings collapsed during the earthquake, killing an estimated 830,000 people.In 1976 another deadly earthquake struck in Tangshan, China, where more than 250,000 people were killed.

 

12. Where and when did the largest earthquake occur in the twentieth century?

The 1960 Chilean earthquake, which occurred off the coast of South America. It had a magnitude of 9.6 and broke a fault over 1,000 miles long.

 

13. What is the distance from the surface of Earth to its center?

The distance from the surface of the Earth to its center is 3,700 miles.

 

14. How were the Hawaiian Islands formed?

The Hawaiian Islands are the tops of gigantic volcanoes that formed above a hot spot in the Earth’s interior. As the volcanoes grew, they were carried away from the hot spot as the Pacific Plate moves northwestward at about 3 1/2 inches per year. The fixed hot spot is currently beneath the southeastern part of the Big Island of Hawaii.

 

15. How much lava has been erupted by Kilauea Volcano during its most recent, long eruption?

Between 1983 and 1997, the volcano erupted 2.1 billion cubic yards of lava. During peak eruption rates, the volcano erupted more than 3/4 million cubic yards of lava daily, enough to fill 75,000 dump trucks, at a rate of nearly one every second.

 

16. Which States have the smallest number of earthquakes in the United States?

Florida and North Dakota.

 

17. How many active volcanoes are located in the State of Alaska?

Alaska has more than 40 historically active volcanoes.

 

18. What is the most earthquake-prone State in the United States?

Alaska is the most earthquake-prone State and one of the most seismically active regions in the world. Alaska experiences a magnitude 7 earthquake almost every year, and a magnitude 8 or greater earthquake on average every 14 years.

 

19. When was the last time that the volcanic mountain Mount Shasta, California, erupted?

The last known eruption occurred approximately 200 years ago. Mount Shasta has erupted, on the average, at least once every 800 years during the last 10,000 years, and about once every 600 years during the last 4,500 years.

 

20. What is the origin of Crater Lake, Oregon?

Crater Lake is of volcanic origin. It lies within the caldera of Mt. Mazama, a volcano of the Cascade Range that erupted 7,700 years ago. The mountain collapsed during its enormous eruption, forming a caldera.

 

21. What is the longest mountain chain on Earth?

The Mid-Atlantic Ridge, which splits nearly the entire Atlantic Ocean north to south. Iceland is one place where this submarine mountain chain rises above the sea surface.

 

22. How much volcanic ash fell during the most vigorous period of the Mount St. Helens eruption?

During the 9 hour period of most vigorous eruptive activity on May 18, 1980, more than 540 million tons of ash fell over an area of more than 22,000 square miles.

 

23. Where do most earthquakes and volcanic eruptions occur on Earth?

The majority of the earthquakes and volcanic eruptions occur along plate boundaries such as the boundary between the Pacific Plate and the North American plate. One of the most active plate boundaries where earthquakes and eruptions are frequent, for example, is around the massive Pacific Plate commonly referred to as the Pacific Ring of Fire.

 

24. What is the "Ring of Fire" and where is it located?

The Ring of Fire is a term for the area surrounding the Pacific Plate where it meets other plate boundaries. It spans the entire west coasts of South America, Mexico, and United States, moves across the Aleutian Islands of Alaska and down the eastern islands of Asia including Japan, and continues southward toward eastern Australia and New Zealand.

 

25. What three countries have the greatest number of historically active volcanoes?

The top three countries are Indonesia, Japan, and the United States in descending order of volcanic activity.

 

26. How many people worldwide will be at risk from volcanoes by the year 2000?

USGS scientists estimate that volcanoes will pose a tangible risk to at least 500 million people by the turn of the century.

 

27. Are volcanoes randomly distributed on the Earth’s surface?

No, most volcanoes are concentrated on the edges of continents or above hot spots (like the Hawaiian islands.

 

28. What percentage of the world’s volcanoes have erupted in the United States over the past 10,000 years?

About 10 percent of the more than 1,500 volcanoes that have erupted in the past 10,000 years are located in the United States. Most of these volcanoes are found in the Aleutian Islands, the Alaska Peninsula, the Hawaiian Islands, and the Cascade Range of the Pacific Northwest.

 

29. Which earthquake was larger, the 1906 San Francisco earthquake or the 1964 Anchorage, Alaska, earthquake?

The 1964 Anchorage earthquake had a magnitude of 9.2, whereas the San Francisco earthquake was a magnitude 7.8. This difference in magnitude equates to over 125 times more energy being released in the 1964 quake and accounts for why the Anchorage earthquake was felt over an area of almost 500,000 square miles.

 

30. Which earthquake was more destructive in terms of loss of life and relative damage costs, the 1906 San Francisco earthquake or the 1964 Anchorage earthquake?

The 1906 San Francisco earthquake. It was responsible for 700 deaths versus 114 from the Anchorage earthquake. Property damage in San Francisco was also greater in relative terms due to the destructive fires.

 

31. What was the most destructive volcanic eruption in the history of the United States?

The 1980 eruption of Mount St. Helens, Washington, was the most destructive volcanic eruption. Fifty-seven people were killed by the eruption including USGS scientist Dr. David Johnston, who was at a monitoring site 5 miles from the volcano on the morning of the eruption. An estimated $1 billion damage was caused by the eruption.

 

32. Approximately how many people lost their lives as the result of volcanic eruptions worldwide during the last 500 years?

Scientists have estimated that at least 300,000 persons lost their lives as a result of volcanic eruptions during the last 500 years. Between 1980 and 1990, volcanic activity killed at least 26,000 people and forced nearly 450,000 to flee from their homes.

 

33. How many of Earth’s volcanoes are known to have erupted in historic time?

About 540 volcanoes on land are known. No one knows how many undersea volcanoes have erupted in historic time.

 

34. What is the newest volcano in the Hawaiian Island chain?

Loihi Seamount, the newest submarine volcano in the Hawaiian Island chain, is forming about 20 miles off the southern coast of the Big Island of Hawaii. Loihi is still 3,180 feet below sea level and is speculated to reach the ocean’s surface in the next 250,000 years.

 

35. How many volcanoes actually form the Big Island of Hawaii?

The Big Island of Hawaii is composed of five volcanoes knitted together. They include Kohala, Mauna Kea, Hualalai, Mauna Loa, and Kilauea.

 

36. How much of the Earth’s surface consists of rocks that are of volcanic origin?

Scientists estimate that more than 3/4 of the Earth’s surface is of volcanic origin-- that is, rocks either erupted by volcanoes or molten rock that cooled below ground and has subsequently been exposed at the surface. Most of Earth’s volcanic rocks are found on the sea floor.

 

37. What causes earthquakes to occur?

An earthquake is caused by the shaking of the ground due to an abrupt shift of rock along a fracture in the Earth, called a fault. Within seconds, an earthquake releases stress that has slowly accumulated within the rock, sometimes over hundreds of years. Most earthquakes are caused by slow movements deep in the Earth that push against the Earth's brittle, relatively thin outer layer, causing the rocks to break suddenly.

 

38. Do you know why California has so many earthquakes, and New York doesn’t?

This is because California lies along the boundary between the Pacific and North American plates and New York is far from a plate boundary. As plate boundaries move past each other, the energy released from the frictional forces that build up cause earthquakes.

 

39. What was Pangaea?

Pangaea was the super continent that began to break up about 225 million years ago, eventually fragmenting into the continents as we know them today.

 

40. Kilauea Volcano has been erupting lava since 1983. What are the primary effects of this eruption on the Island of Hawaii?

Lava from the eruption of Kilauea has covered about 40 square miles of rain forest and grassland, paved 8 miles of highway, destroyed 181 homes and other structures valued at $61 million, and added almost 600 acres of new land to the Island of Hawaii. In addition, the release of sulfur dioxide gas during the ongoing eruption has led to volcanic air pollution and acid rain on parts of the island.

 

 

41. When did the Hawaiian Island chain of volcanoes begin to form?

The Hawaiian Island chain began to form more than 70 million years ago. On the Island of Hawaii, Kilauea, Mauna Loa, and Hualalai volcanoes have erupted in the past 200 years. East Maui Volcano, commonly known as Haleakala, on the island of Maui, is the only other Hawaiian volcano to have erupted since the late 1700's.

 

42. Where are most of Earth’s volcanoes located?

Most of the world’s volcanoes are located on the seafloor. The most prominent topographic feature on Earth is the immense volcanic mountain chain that encircles the planet beneath the sea--the chain is more than 30,000 miles long and rises an average of 18,000 feet above the seafloor. This volcanic chain is called the mid- ocean ridge and is where Earth’s plates are spreading apart as new crust is formed by volcanic activity.

 

43. What volcano produced the world’s most costly eruption in terms of human fatalities?

The eruption of Tambora volcano in Indonesia in 1815 is estimated to have killed about 90,000 people. Most of the people died from starvation after the eruption because of widespread crop destruction, and from water contamination and disease.

 

44. How many active volcanoes exist in Japan?

There are more than 75 active volcanoes in Japan. One of the more recent eruptions occurred on the island of Kyushu, about 25 miles east of Nagasaki, where the Unzen Volcano awakened after a 200 year slumber to erupt a new lava dome at its summit.

 

45. What was the worst volcanic disaster to occur in Japan?

A volcanic landslide in 1792 on Unzen volcano killed more than 15,000 people--the worst volcanic disaster in the country's history. The landslide swept into the sea and triggered a destructive tsunami that destroyed many fishing villages.

 

46. What are tsunamis and how are they caused?

A tsunami is a large wave caused by earthquakes, submarine landslides, and, infrequently, by eruptions of island volcanoes. During a major earthquake, an enormous amount of water can be set in motion as the seafloor moves up and down. The result is a series of potentially destructive waves that can move at more than 500 miles per hour.

 

47. What is the longest fault found in California?

The San Andreas is the longest fault found in California; it extends from Point Delgado, in northern California southward to Mexico.

 

48. For what is the Richter scale used?

The Richter scale is a numerical scale used to measure the magnitude of an earthquake. It was developed in 1935 by Charles Richter at the California Institute of Technology.

 

49. What is a composite volcano?

A composite volcano is a steep-sided, symmetrical cone of large dimension built around layers of lava flows, volcanic ash, and cinders that may rise as much as 8,000 feet or more above their bases. Some of the best-known composite volcanoes include Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mayon volcano in the Philippines, Mount Shasta in California, and Mount Rainier in Washington.

 

50. How old is the oldest island in the Hawaiian Island chain?

The volcanoes of Kauai and Niihau islands at the northern end of the chain are about 5 1/2 million years old.

USGS Earth Science Information Center-U.S. Department of the Interior, U.S. Geological Survey, Reston, VA