Unit E Lesson E12 Hot Spots
Completion requirements
Lesson E12: What is a Hot Spot?
Video Lesson
Many of Earth’s volcanoes occur at converging plate boundaries. One plate is subducted under another, and the melting rock of the subducted plate rises through cracks in boundary with the other plate to form volcanoes. But what about volcanoes such as
those on the Hawaiian Islands or in Yellowstone National Park? No plate boundaries and no subductions are near these areas of volcanic activity. These volcanoes are explained as hot spots.
Lesson E12: What is a Hot Spot?
What is a Hot Spot?
Earth has many volcanoes, but they are not all the same. Volcanic arcs of islands, such as the Azores and Aleutians, can form when one tectonic plate is subducted under another. The volcanoes of the Pacific Northwest, such as Mount St. Helens and Mount Rainier, form in this same way. Islands such as Hawaii, Samoa, Easter Island, and French Polynesia, and areas such as Yellowstone National Park are different. These volcanoes are far from plate boundaries. They form as tectonic plates pass over what are called ‘hot spots’ in the mantle below.
Earth has many volcanoes, but they are not all the same. Volcanic arcs of islands, such as the Azores and Aleutians, can form when one tectonic plate is subducted under another. The volcanoes of the Pacific Northwest, such as Mount St. Helens and Mount Rainier, form in this same way. Islands such as Hawaii, Samoa, Easter Island, and French Polynesia, and areas such as Yellowstone National Park are different. These volcanoes are far from plate boundaries. They form as tectonic plates pass over what are called ‘hot spots’ in the mantle below.
Reading and Materials for This Lesson
Science in Action 7
Materials:
Science in Action 7
Reading: Page 400
Materials:
cardboard, scissors, pointed knife for making holes in the cardboard, squeezable tube of toothpaste, a pan or sheet of newspaper to catch any mess
A plume of hot mantle melts a hole through the solid rock of the tectonic plate passing above it, and the rising magma forms a volcano at the surface. The tectonic plate keeps moving, and the hot spot melts another hole in the tectonic plate and forms another volcano as the original volcano becomes dormant. The result is a trail of volcanic footprints left in the plate as it passes.
Figure E.3.12.1 – The youngest Hawaiian Islands, from right (youngest) to left: Hawaii, Maui, Molokai, Oahu, Kauai.
Figure E.3.12.2 – Puu Oo is an active cone volcano in Hawaii. It has been erupting continuously since 1983.
Tuzo Wilson, Hot Spots, and Mantle Plumes
The Hawaiian Islands are a very remote chain of more than 100 islands in the middle of the Pacific Ocean. Geologically, the Hawaiian Islands are not near any plate boundary, which is very odd considering the islands are volcanic. The big island of Hawaii is the largest, and has the only active volcano.
Click here to look at the islands, then zoom out and follow the island chain to the left and northward.
Hawaii was confusing for geologists who were working to understand plate tectonics and to decide if Alfred Wegener was correct about the idea of continental drift. In 1963, Canadian Tuzo Wilson proposed that the Hawaiian Islands were the result of a hot spot deep below the islands. Or, more specifically at that time, beneath the big island of Hawaii.
The Hawaiian Islands are a very remote chain of more than 100 islands in the middle of the Pacific Ocean. Geologically, the Hawaiian Islands are not near any plate boundary, which is very odd considering the islands are volcanic. The big island of Hawaii is the largest, and has the only active volcano.
Click here to look at the islands, then zoom out and follow the island chain to the left and northward.
Hawaii was confusing for geologists who were working to understand plate tectonics and to decide if Alfred Wegener was correct about the idea of continental drift. In 1963, Canadian Tuzo Wilson proposed that the Hawaiian Islands were the result of a hot spot deep below the islands. Or, more specifically at that time, beneath the big island of Hawaii.
Figure E.3.12.3 – Magma rising from the hot spot forms a volcano on the surface of the plate above it. As the plate moves past, the magma rises in a new location and forms a newer volcano.
Wilson thought a very hot location deep in Earth’s mantle was directly below where the big island is now. The huge Pacific tectonic plate on which Hawaii is in the middle is moving slowly to the northwest. As it does, the plate moves slowly over this
hot spot of rising mantle. Considering
the other islands in the chain
revealed the path that the Pacific Plate has been moving for millions of years. Each island and submerged island was built up when that location was over the hot spot. Since then, the volcanic peaks and islands have been worn away.
Figure E.3.12.4 – The Hawaiian Island chain has not followed a straight path. Currently, the hot spot is at location #3.
Figure E.3.12.5 – Hundreds of years ago, Native Hawaiians realized their islands became older and older towards the northwest.
Therefore, the chain of Hawaiian Islands is a set of tracks that shows the direction and speed that the Pacific Plate has been moving for the past 85 million years. Measurements reveal that the Pacific Plate is moving northwest at a speed of about 5 to
10 cm per year.
Deep below the Hawaiian Islands is thought to be a mantle plume of extraordinary size. The incredible heat of the core and mantle forms convection currents in the fluid portions of the Earth’s interior. Likely, certain locations are even hotter than usual for plumes, and these superheated sections of mantle rise even more quickly than usual convection currents do. These plumes of mantle can push up and into the lithosphere, melting through the rock of the tectonic plates – think of a blowtorch below a sheet of metal. Rising magma heats the plate, forming magma chambers. Then, volcanoes in the plate release the pressure momentarily.
Hot spots are difficult to measure, and they are impossible to view directly. Currently, geologists are working on the idea of mantle plumes and hot spots, and they continue to find new evidence that helps them to refine the idea. One interesting observation is that many hot spots might exist in various locations on Earth’s crust – not only under the Hawaiian Islands.
Deep below the Hawaiian Islands is thought to be a mantle plume of extraordinary size. The incredible heat of the core and mantle forms convection currents in the fluid portions of the Earth’s interior. Likely, certain locations are even hotter than usual for plumes, and these superheated sections of mantle rise even more quickly than usual convection currents do. These plumes of mantle can push up and into the lithosphere, melting through the rock of the tectonic plates – think of a blowtorch below a sheet of metal. Rising magma heats the plate, forming magma chambers. Then, volcanoes in the plate release the pressure momentarily.
Hot spots are difficult to measure, and they are impossible to view directly. Currently, geologists are working on the idea of mantle plumes and hot spots, and they continue to find new evidence that helps them to refine the idea. One interesting observation is that many hot spots might exist in various locations on Earth’s crust – not only under the Hawaiian Islands.
Figure E.3.12.6 – After the plate passes the hot spot, the island no longer receives fresh magma.
Figure E.3.12.7 – 1 : Divergent plate boundaries ; 2 : Transform plate boundaries ; 3 : Convergent plate boundaries ; 4 : Plate boundary zones ; 5 : Selected prominent hotspots.
Figure E.3.12.8 – Each hot spot is marked with a dot on this map. The larger the dot, the more energy that hot spot is thought to contain.
Other Interesting Hot Spots
Look at the various maps of suspected hot spots. Hot spots are found near diverging plate boundaries such as the Mid-Atlantic Ridge, converging boundaries such as the Pacific Northwest of North America, transform boundaries such as the Samoan Islands, and in the middle of huge tectonic plates such as the Hawaiian Islands. In other words, no pattern is evident between hot spot location and plate tectonics. Mantle plumes are not concerned with what is above them. They melt through everything equally as it passes. The feature that is common to all hot spots is volcanoes.
Look at the various maps of suspected hot spots. Hot spots are found near diverging plate boundaries such as the Mid-Atlantic Ridge, converging boundaries such as the Pacific Northwest of North America, transform boundaries such as the Samoan Islands, and in the middle of huge tectonic plates such as the Hawaiian Islands. In other words, no pattern is evident between hot spot location and plate tectonics. Mantle plumes are not concerned with what is above them. They melt through everything equally as it passes. The feature that is common to all hot spots is volcanoes.
Iceland
Iceland is one of the most volcanic locations on Earth. It is also geologically complex. Geologists believe that Iceland is the location of a hot spot on top of a subduction zone on a converging boundary. It has hot spot volcanoes in a volcanic arc of islands. Likely, Iceland is an island only because both types of volcanoes are there. Either type on its own would not produce enough lava on the surface to keep the island above sea level.
Iceland is confusing for geologists because evidence that Iceland’s islands have moved over time, similar to the Hawaiian Island chain, is lacking. Further studies of Iceland’s interesting geology continue!
Iceland is one of the most volcanic locations on Earth. It is also geologically complex. Geologists believe that Iceland is the location of a hot spot on top of a subduction zone on a converging boundary. It has hot spot volcanoes in a volcanic arc of islands. Likely, Iceland is an island only because both types of volcanoes are there. Either type on its own would not produce enough lava on the surface to keep the island above sea level.
Iceland is confusing for geologists because evidence that Iceland’s islands have moved over time, similar to the Hawaiian Island chain, is lacking. Further studies of Iceland’s interesting geology continue!
Figure E.3.12.9 – After the plate passes the hot spot, the island no longer receives fresh magma.
Figure E.3.12.10 – Old Faithful, in Yellowstone National Park, is a huge geyser that erupts hot water and steam..
Figure E.3.12.11 – Yellowstone National Park is a land-based hot spot.
Yellowstone National Park
Yellowstone National Park is famous for its geysers such as Old Faithful. All the energy that causes that groundwater to boil and erupt from the ground comes from a hot spot deep below the park.
The Yellowstone hot spot has left behind a trail of lava flows across several states to the west of Yellowstone National Park. It has been responsible for some enormous super-eruptions during the past 70 million years. The last to occur was 640 000 years ago. Historically, it appears that this hot spot results in a super-eruption every 600 000 to 800 000 years. These have had devastating effects over a very wide area. When it occurs again, it will disrupt almost all aspects of modern life on Earth.
Figure E.3.12.12 – The Yellowstone hot spot has moved slowly to the east over millions of years.
Anahim Peak
Anahim Peak is a dormant volcano in central British Columbia. It is one in a chain of volcanoes from a hot spot located between two ranges of volcanic mountains called the Rainbow Range and the Ilgachuz Range. Currently, the hot spot is below a small mountain called the Nazko Cone, east of the other volcanoes in the series. The Nazko Cone has not erupted for 7000 years, but in 2007 a series of small earthquakes indicated activity below.
Anahim Peak was a very important source of obsidian for the First Nations living in that area for hundreds of years. The obsidian was made into sharp-edged tools, and it was traded throughout the region for other goods.
Anahim Peak is a dormant volcano in central British Columbia. It is one in a chain of volcanoes from a hot spot located between two ranges of volcanic mountains called the Rainbow Range and the Ilgachuz Range. Currently, the hot spot is below a small mountain called the Nazko Cone, east of the other volcanoes in the series. The Nazko Cone has not erupted for 7000 years, but in 2007 a series of small earthquakes indicated activity below.
Anahim Peak was a very important source of obsidian for the First Nations living in that area for hundreds of years. The obsidian was made into sharp-edged tools, and it was traded throughout the region for other goods.
Figure E.3.12.14 – British Columbia also has a hot spot that is moving slowly.
Try It!
Toothpaste Hot Spot
This experiment explores the formation of a volcanic island chain from the action of a hot spot below Earth’s crust. You will use toothpaste to simulate the rising magma from the hot spot. The cardboard moving slowly over the toothpaste simulates the motion of a tectonic plate over a mantle plume.
Materials:
This experiment explores the formation of a volcanic island chain from the action of a hot spot below Earth’s crust. You will use toothpaste to simulate the rising magma from the hot spot. The cardboard moving slowly over the toothpaste simulates the motion of a tectonic plate over a mantle plume.
Materials:
- cardboard, such as a cereal box
- scissors
- pointed knife for making holes in the cardboard
- squeezable tube of toothpaste
-
a pan or sheet of newspaper to catch any mess
Safety Warning
Take care with the sharp knife and scissors; don't cut yourself or anyone else!
Download:
DOWNLOAD this document. It provides a space for you to write answers to questions later in this activity.
Instructions:
DOWNLOAD this document. It provides a space for you to write answers to questions later in this activity.
Instructions:
1. Cut a strip of cardboard that is easy to hold in one hand, about 10 cm x 30 cm.
2. Use the knife very carefully to make a series of about 8 holes in a rough line along the cardboard. Make some larger than others, but none larger than the spout of the toothpaste tube. Make some in small groups of two or three.
3. Remove the cap on the toothpaste tube and be sure the paste will flow freely from the tube when you squeeze gently.
4. Hold the cardboard in one hand and place the toothpaste tube below the first hole in the cardboard. Be sure the pan or sheet of newspaper is underneath to catch any toothpaste mess that falls.
5. Squeeze the toothpaste tube gently until you see it emerge from the first hole in the cardboard. Observe what happens.
6. Continue to squeeze the tube gently with one hand while you move the cardboard carefully (and slowly) to the next hole. The toothpaste stops flowing through the first hole and starts flowing through the second hole or set of holes. Observe what happens.
7. Continue moving the cardboard slowly until the toothpaste has flowed through all the holes. Observe what happens.
Questions:
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
The tube of toothpaste is the hot spot and toothpaste is the magma it pushes through the crust. The cardboard is the crust that the magma flows through to form the volcanoes above. The holes in the cardboard represent the cracks or vents in the crust
that the magma flows through to get to the surface. The squeezed toothpaste tube represents a mantle plume and the hot magma that rises to the surface. These are good models for what they represent -- except that heat energy and convection
of the mantle is not represented.
A hot spot is a location deep in Earth’s mantle that sends very hot magma towards the surface. Likely, hot spots do not move, or they move very little. The tectonic plates on Earth's surface move -- but very slowly. Therefore, moving the cardboard is
more realistic than moving the toothpaste tube is.
Smaller holes reduce the volume of toothpaste, but they allow the mounds of paste to grow taller. Larger holes and multiple holes close together increase the volume of toothpaste flow, which increases the size of the paste islands that form.
In this model, the toothpaste islands first rise tall, then they spread slowly on the surface of the cardboard. This is not really erosion, but it shows the toothpaste islands decreasing in height over time. The Hawaiian Islands erode over time, so the
older islands are much smaller than newer islands are.
If a cereal box represents a thin oceanic plate, a thicker piece of cardboard or styrofoam could be used to represent a thicker continental plate. This probably would require more toothpaste to make a volcano.
There is no Self-Check for this lesson. Please continue to the next lesson.