Photo showing the aftermath of an earthquake on a town street
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The Great Alaska Earthquake Mystery

How the most powerful earthquake in U.S. history changed science forever 

By Lauren Tarshis

Learning Objective: Students will explain how one scientist used evidence from the Great Alaska Earthquake to make discoveries about plate tectonics.

Lexile: 750L; 510L
Other Focus Areas: Engineering, Measurement & Data
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PETER HAEUSSLER/USGS

George Plafker

Scientist George Plafker stared out of the airplane window in horror. He was flying low over Alaska. Two days before, on March 27, 1964, the state had been struck by what is still the most powerful earthquake in United States history.

The massive earthquake lasted more than four minutes—about 20 times as long as most earthquakes! The quake triggered giant ocean waves. Dozens of people lost their lives.

Plafker, who was 34 years old at the time, is a geologist. That’s a scientist who studies Earth. He was not an earthquake expert—not yet. But he had spent time in Alaska when he first started as a geologist. He’d fallen in love with the Alaskan wilderness—the towering mountains and wide rushing rivers, the thrill of seeing grizzlies and moose and wolves in the wild.

Scientist George Plafker was in an airplane. He was flying low over Alaska. He sat staring out of the plane’s window. He looked down at the ground in horror. An earthquake had struck the state just two days before. It happened on March 27, 1964. It was the most powerful earthquake in United States history.

The huge earthquake lasted more than four minutes. That’s about 20 times longer than most earthquakes! The quake triggered giant ocean waves. Dozens of people lost their lives.

Plafker was 34 years old at the time. He’s a geologist. That’s a scientist who studies Earth. He was not an earthquake expert. At least, not yet. But he had spent time in Alaska. It was when he first became a geologist. He’d fallen in love with the Alaskan wilderness. He loved the towering mountains and wide rushing rivers. And he was thrilled to see grizzlies, moose, and wolves in the wild. 

JIM MCMAHON/MAPMAN® 

The U.S. government needed scientists at the scene of the earthquake to study the aftermath up close. Plafker was eager to help. And now, flying low in the gray Alaskan sky with two other scientists, he was stunned by the shattered land below.

In Anchorage, Alaska’s biggest city, buildings had collapsed. Houses had tumbled into the ocean. Streets looked like they’d been split in half by a giant ax. Mountaintops had exploded apart. Huge waves called tsunamis had drowned forests and had turned towns into jumbles of wreckage.

Scientists had known that Alaska was prone to earthquakes. In fact, more earthquakes happen in Alaska than in any part of the United States! But most are very mild and last for just a few seconds. Few scientists—and even fewer Alaskans themselves—worried about a powerful earthquake striking.

How had this happened? Plafker was determined to figure it out. He had no idea that what he would learn in Alaska would change science forever.

The U.S. government wanted scientists at the scene of the earthquake. They were needed to study the aftermath up close. Plafker was ready to help. And now, he was flying through the gray Alaskan sky. There were two other scientists with him. He was stunned by the broken land below.

Anchorage is Alaska’s biggest city. Its buildings had collapsed. Houses had tumbled into the ocean. Streets looked like they’d been split in half by a giant ax. Mountaintops had burst apart. Huge waves had drowned forests. They’re called tsunamis. They’d also turned towns into rubble. 

Scientists had known that Alaska was prone to earthquakes. In fact, more earthquakes happen in Alaska than in any other part of the United States! But most are very mild. They last for just a few seconds. Few Alaskans worried about a powerful earthquake striking. And neither did most scientists.

How had this happened? Plafker wanted to find out. He had no idea what he would learn. But it would change science forever.

SCIENCE HISTORY IMAGES/ALAMY STOCK PHOTO (TSUNAMI); MARKA/UNIVERSAL IMAGES GROUP VIA GETTY IMAGES (WRECKED CAR)

Left: Giant waves created by the earthquake damaged coastal towns. Right: Shaking buildings crumbled apart.

Shock Waves Explode

Every year, there are about 500,000 earthquakes around the world. Of those, only about 100 are strong enough to cause damage. Most are so mild that no one even feels any shaking.

All earthquakes—big and small—happen because of sudden movements in Earth’s crust. This is our planet’s outermost layer. It’s the ground that holds up your school, your town, our oceans, and our mountains. Many miles thick, the crust is broken up into about 17 plates. These rest atop a layer of molten rock—Earth’s mantle.

Earth’s plates are always moving, in very slow motion, over the mantle. (See Where Earth’s Plates Meet) Sometimes two plates get stuck together. They push and grind against each other. Over years and years, pressure builds. Then, with sudden violence, the plates break free. Shock waves explode in all directions. Up top, on Earth’s surface, everything shakes. That’s an earthquake.

Earthquake scientists know all of this today. But at the time of the Alaska earthquake, in 1964, seismology was still a new science. Some important ideas had not been proved. Scientists knew that Earth’s crust was broken up into giant plates. They understood that earthquakes were caused by movements deep inside Earth’s crust. They knew there were giant cracks in the crust—these are called faults. It was even clear that most earthquakes happened because of movements at those faults.

But like a puzzle with missing pieces, scientists’ understanding of earthquakes had gaps. And there was one very big gap: Scientists hadn’t proved that Earth’s plates were always moving in slow motion.

Today scientists know this idea as the theory of plate tectonics. It is one of the most important theories in geology. But in the 1960s, only some scientists supported the idea. They needed more evidence to back it up.

In the shattered land of Alaska, George Plafker’s hunt for that evidence began.

About 500,000 earthquakes happen around the world every year. Of those, only about 100 are strong enough to cause damage. Most are so mild that no one even feels any shaking.

All earthquakes happen for the same reason. They’re caused by sudden movements in Earth’s crust. This is our planet’s outer layer. It’s the ground that holds up your school, your town, oceans, and mountains. The crust is many miles thick. It’s broken up into about 17 pieces. They’re called plates. These rest atop a layer of molten rock. It’s called Earth’s mantle.

Earth’s plates are always moving. They shift in very slow motion over the mantle. (See Where Earth’s Plates Meet.) Sometimes two plates get stuck together. They push and grind against each other. Pressure builds over years and years. Then the stuck plates violently break free. Shock waves ripple in all directions. Everything shakes on Earth’s surface above. That’s an earthquake.

Earthquake scientists know all of this today. But not in 1964, at the time of the Alaska earthquake. Seismology was still a new science back then. Some big ideas had not been proved. Scientists knew that giant plates made up Earth’s crust. They knew that motion deep inside Earth’s crust caused earthquakes. They knew there were giant cracks in the crust. These cracks are called faults. Scientists even knew about shifts along those faults. They led to most earthquakes.

But what scientists knew about earthquakes had gaps. It was like a puzzle with missing pieces. One of the biggest gaps had to do with Earth’s plates. Scientists hadn’t proved that they were always slowly moving.

Today this is known as plate tectonics. It is one of the most important ideas in geology. But only some scientists believed in the idea in the 1960s. They needed more evidence to back it up.

George Plafker’s hunt for that evidence began in Alaska.

Searching for Clues

As Plafker flew over Alaska in the days after the earthquake, his job was to study the effects of the disaster. He traveled over thousands of square miles. He spoke to survivors. After two weeks, he returned home. Plafker and his team wrote a report of their findings. Their project, it seemed, was finished.

But a huge question still bothered Plafker: What had caused this earthquake?

According to scientists’ understanding at the time, there must be a fault under the disaster zone. When Plafker was flying around, he had been looking for a fault—a miles-long crack in the ground. But he hadn’t seen one! The cause of the most powerful earthquake in U.S. history was a mystery.

Plafker couldn’t let it go. So he returned to Alaska later that spring. He was determined to solve it.

Plafker had some tools to do his work but nothing like what scientists use today. Now geologists rely on powerful computers and sensitive instruments to learn about rocks miles below Earth’s surface. Such tools didn’t exist in 1964. Plafker would have to rely on his eyes and his brain—his powers of observation.

Plafker spent two months traveling across areas torn apart by the earthquake. Like a detective trying to solve a crime, he searched for clues. One clue was that the land just off the coastline had been lifted by as much as 30 feet. It was as though an underground giant had hoisted the land up over its head. In other places, the land had dropped, as though the same muscled giant had yanked it down.

Plafker discovered the changes in the seafloor in a surprising way: by studying sea creatures called barnacles that turned up in a place he didn’t expect. These tiny creatures spend their lives attached to hard surfaces in the sea and along shorelines. To survive, they must be covered with water at least part of the time. On many cliffsides along Alaska’s coast, Plafker observed, the barnacles were dead.

Before the earthquake, the cliffs had been covered with water. Now there was a row of dried-up barnacles many feet above the water. To Plafker, this was evidence that parts of the seafloor had shifted up because of the earthquake.

But how had that happened?

Plafker’s job was to study the effects of the earthquake. He traveled over thousands of square miles in the days after the disaster. He spoke to survivors. He returned home after two weeks. Plafker and his team wrote a report of their findings. It seemed their project was finished.

But a huge question still bothered Plafker. What had caused this earthquake?

Scientists thought there must be a fault under the disaster zone. Plafker had looked for one as he flew overhead. But he hadn’t seen a miles-long crack in the ground! The cause of the most powerful earthquake in U.S. history was a mystery.

Plafker couldn’t let it go. So he returned to Alaska later that spring. He felt he had to figure out what had happened.

Plafker had some tools to do his work. But they were nothing like what scientists use today. Now geologists rely on powerful computers. They use sensitive instruments. This allows them to learn about rocks miles below Earth’s surface. Such tools didn’t exist in 1964. Plafker would have to rely on his eyes and brain. He also had his powers of observation.

Plafker spent two months traveling across areas torn apart by the earthquake. He was like a detective trying to solve a crime. He searched for clues. He found that the land just off the coastline had been lifted. It shifted by as much as 30 feet. It was like an underground giant had pushed the land up. The land had dropped in other places. It was like it had been yanked down.

Plafker made the discovery in a surprising way. He studied tiny sea creatures. They’re called barnacles. They spend their lives stuck to hard surfaces in the sea and along shorelines. They must be covered with water at least part of the time. Otherwise, they won’t survive. Plafker observed barnacles on cliffsides along Alaska’s coast. But many were dead.

That meant water must have covered the cliffsides before the earthquake. Now there were dried-up barnacles many feet above the water. To Plafker, this was evidence that parts of the seafloor had shifted up.

But how had that happened?

USGS (THEN); SHUTTERSTOCK.COM (BARNACLES); DESIGN PICS INC/ALAMY STOCK PHOTO (NOW); 

THEN: In 1964, Plafker noticed dead barnacles on newly dry cliffs. It gave him new ideas to explain how Earth moved.

NOW: Today geologists have powerful tools to study Earth. Their work builds on the efforts of scientists like Plafker.

A New Understanding

Plafker returned home to California. He spent weeks reviewing his data. He’d taken hundreds of measurements of where the land had been lifted and where it had fallen. He’d taken many notes and photographs. He spent hours thinking.

Plafker’s mind kept returning to the idea that Earth’s plates were moving—the theory that would become known as plate tectonics. He read all he could about it. He spoke to other geologists to hear their ideas.

Two of those giant plates were near the disaster zone—that much was certain. One plate held up the Pacific Ocean. The other held up the continent of North America. Based on all Plafker had learned, it was clear that those plates had to be moving—and pushing against each other. And if that was right, the fault he was looking for was actually the place where the two plates jammed together!

Plafker concluded the Pacific plate pushed into and under the North American plate. Pressure had been building for centuries. Until finally, at that terrifying moment on March 27, 1964, the plates finally broke free. That caused the Alaska earthquake. And it’s why parts of the land and seafloor had popped up and parts had dropped down. (See How Plates Move.)

The more Plafker considered this idea, the more certain he was. Not only did it explain the cause of the Great Alaska Earthquake but the evidence supported the idea of plate tectonics.

Would other scientists agree with him?

They did. Over time, Plafker’s work in Alaska transformed science. Today, at the age of 94, George Plafker is honored as one of the world’s most important geologists. His work has helped scientists learn more about where and when powerful earthquakes are likely to happen. This helps communities at risk keep people safer. Buildings like schools can be built to stay standing in an earthquake.

We can’t stop what’s happening miles under the earth’s surface. But when the ground starts to shake, this knowledge helps us be better prepared.

Plafker returned home to California. He spent weeks looking over his data. He’d taken hundreds of measurements. They showed where the land had been lifted. They also showed where it had fallen. He’d taken many notes and pictures. He spent hours thinking.

Plafker’s mind kept returning to one idea. Earth’s plates must be moving. This is the theory that would become known as plate tectonics. He read all he could about it. He spoke to other geologists to hear their ideas. 

Two of those giant plates were near the disaster zone. That much was certain. One plate held up the Pacific Ocean. The other held up the continent of North America. Plafker thought about all he’d learned. He felt it was clear that those plates had to be moving. They’d been pushing against each other. And suddenly he knew where to find the fault he’d been looking for! It was the place where the two plates jammed together.

Plafker realized the Pacific plate pushed into and under the North American plate. Pressure had been building for centuries. Then the plates finally broke free. That caused the terrifying earthquake on March 27, 1964. And it’s why parts of the land and seafloor had popped up and parts had dropped down. (See How Plates Move.)

Plafker kept thinking about this idea. He became more certain it was right. It explained the cause of the Great Alaska Earthquake. And it supported the idea of plate tectonics.

Would other scientists agree with him?

They did. Over time, Plafker’s work in Alaska changed science. Today Plafker is 94. He’s seen as one of the world’s most important geologists. His work has helped scientists learn more about earthquakes. That includes where and when powerful ones are likely to happen. This helps communities at risk keep people safer. Buildings like schools can be built to stay standing in an earthquake.

We can’t stop what’s happening miles under the earth’s surface. But this knowledge helps us be better prepared when the ground starts to shake.

video (1)
Games (1)
Slideshows (1)
Activities (6) Download Answer Key
Quizzes (1)
Step-by-Step Lesson Plan

1.  PREPARE TO READ (10 minutes)
Watch a video about earthquakes and model how tectonic plates move.

  • Ask students to turn and talk with a partner, sharing what they know about earthquakes. Then play the video What You Need to Know About Earthquakes.” Discuss key ideas about earthquakes mentioned in the video.
  • Have students place both hands palms-down and fingers closed on their desks, with only their thumbs touching. Tell them to imagine that their hands are two different tectonic plates—the giant slabs of rock that make up Earth’s crust. Ask: Keeping your hands on the desk, what are three ways your plates can move? (toward each other, away from each other, and slipping past each other) Have students push their hands together and feel the pressure build. Then have them lift one thumb slightly. Discuss what happened. (Their hands suddenly moved toward each other, and one hand slid partly under the other.) Explain that two tectonic plates moved like this in 1964 and caused a major earthquake!

2. READ AND REFLECT (10 minutes)
Read the article and determine its main ideas.

  • Preview the article’s vocabulary (p. 4) using the Vocabulary Slideshow. Hand out the What’s the Main Idea? graphic organizer. Tell students you are going to note big ideas in the article as you read. Read the article aloud, pausing after each section to note its main idea and supporting details. Analyze the “How Plates Move” diagram (p. 9).
  • Have students use the article as a reference to complete the Quick Quiz. Reconvene to discuss their answers. (Revisit the video and the kinesthetic model of earthquakes from step 1 above to reinforce ideas as needed.)

3. RESPOND TO READING (25 minutes)
Build and test an earthquake-resistant structure.

  • You’ll need about 40 mini marshmallows and 80 toothpicks per group. (Limit the number of marshmallows and toothpicks if needed.) One 10-ounce bag of mini marshmallows and two 250-count boxes of toothpicks should provide enough materials for six groups of students. We recommend three to four students per group.
  • Make one shake table in advance to use as a model (steps 1-2). You can precut all the cardboard pieces in advance if your students need extensive support to cut them. (You could make one shake table for the class. Then you can have groups test their structures as they finish them, or test all the structures together and have the whole class observe.)
  • Demonstrate how to use the shake table. Test a paper or plastic cup on it, first right-side up and then upside down. Ask students what they notice. (A wider base gives the cup better balance.) Hand out the Design an Earthquake-Resistant Structure activity and have students complete it in small groups.

Text-to-Speech