Monitoring Volcanoes

Question 1

Before a volcano erupts, scientists watch for certain clues. Which two clues would most likely show that the volcano is getting ready to erupt?

Accepted Answer

The ground lifts a few centimeters and small earthquakes happen nearby.

Answer

The sky turns bright blue and birds fly in larger flocks around the volcano.

Answer

Children in the town start singing louder during school assemblies.

Answer

The area receives more rain and a new lake forms near the volcano.

Question 2

Dr. Liu is watching Volcano Zephyr. She notices the ground is bulging a little, the smell of sulfur gas is getting stronger, and tiny earthquakes are occurring. She can say an eruption might be coming, but she cannot tell the exact day or hour it will happen. Which explanation best shows why her prediction cannot give an exact time?

Accepted Answer

The volcano’s underground pressure can change suddenly, so the signs she measured can appear at different times before an eruption.

Answer

If any one warning sign appears, the eruption will happen at a known, fixed time.

Answer

Scientists never give exact times because they want to keep the public nervous.

Answer

The devices that measure gas and earthquakes are always broken, making the data useless.

Question 3

Dr. Maya is monitoring volcano Solara. In the last five days she has recorded three observations: 1) The ground around the crater has risen a few centimeters. 2) The smell of sulfur gas near the summit has become a little stronger. 3) A handful of tiny earthquakes have been detected. Which statement best explains why Dr. Maya will wait until she sees all three kinds of observations before saying the volcano is likely to erupt soon?

Accepted Answer

Because any one of those signs can happen without an eruption, but when several different signs occur together they give a stronger overall picture that an eruption may be approaching.

Answer

Because the ground swelling is the most important clue, so the gas smell and tiny earthquakes are only extra details that don’t affect the risk assessment.

Answer

Because a stronger sulfur smell by itself proves that the volcano will erupt within the next 24 hours.

Answer

Because the tiny earthquakes are the only reliable warning, and the other observations can be ignored.

Try three questions

Before a volcano erupts, scientists watch for certain clues. Which two clues would most likely show that the volcano is getting ready to erupt?

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