5.6 G 1/29

Rising Corals

6Scientists know a lot about earthquakes after they happen, but they can’t predict
what hour, day, year, or even decade an earthquake will hit. So how did Kerry Sieh
know to warn the Tello islanders that an earthquake might happen soon? He read the
corals.

7In the Indian Ocean, big corals called Porites grow from the sea floor to the water’s
surface, then outward. The ocean floor sinks slowly between earthquakes, dragging
the coral down, then rises quickly during a quake, raising the coral up again. Over
hundreds of years, all this up and down causes the coral to grow outward in
doughnut-shaped rings. Sieh discovered that by looking at the growth patterns of
Porites coral heads near the fault, he could pinpoint the dates of past earthquakes,
and maybe find a pattern that would help predict future quakes.

8Using underwater chainsaws, Sieh and other scientists sliced off slabs of coral heads
that were hundreds of years old. Sure enough, they found that, on a section of the
fault just to the north of the Mentawai Islands and just to the south of Tello,
earthquakes occurred in pairs about every 200 years. One pair of quakes hit in the
1300s, another in the 1500s, and a third in 1797 and 1833—almost 200 years ago.
According to the corals, it was time for another big quake.

What are some important details from the section “Rising Corals”?

Paragraph 6

Paragraph 7

●Scientist can’t predict
what hour, day, year,
or even decade an
earthquake will hit.

Paragraph 8

●Scientist found that, on a
section of the fault just to
the north of the Mentawai
Islands, earthquakes
occurred in pairs about
every 200 years.

●Indian Ocean, big corals called Porites

●The ocean floor sinks slowly between earthquakes, dragging
the coral down, then rises quickly during a quake, raising the
coral up again.

●pinpoint the dates of past earthquakes, and maybe find a
pattern that would help predict future quakes.

Key Idea

“Rising Corals”

What key idea is supported by
the details in the section “Rising
Corals”?

A.

Scientists won’t be able to
predict natural disasters in
the Indian Ocean.

B.

Scientists would be able to
predict earthquakes by
analyzing corals in the
Indian Ocean.

C.

Porites are big corals that
can be found in the Indian
Ocean’s floor after an
earthquake.

D.

Scientists think that
earthquakes must happen
every 200 years in the
Indian Ocean.

28

30

This question has two parts. First, answer Part A. Then answer Part B.

Part A
In paragraph 9, what key idea supports that the islands in the Indian Ocean can sink?

A.

It gives specific information about the Sunda Megathrust Fault.

B.

It explains how the plates are formed in the Indian Ocean.

C.

It gives information about how plates collide and join together producing negative outcomes.

D.

It tells about how frequent earthquakes and tsunamis happen in the Sunda Megathrust Fault.

Part B
Which sentence or phrase from the text best supports the answer to Part A?

A.

The corals weren’t the only evidence of underground rumblings in Indonesia.

B.

The islands on top of the continental plate are dragged down too, as much as half an inch a year.

C.

Between earthquakes, the plates are stuck together.

D.

The more years between earthquakes, the more the islands sink — and the more stress builds up…