Related Links

Hawai'i Volcanoes National Park webpage

• Links (including Just For Kids!)

Animations from Essentials of Geology by Stephen Marshak

• Hot spot animation
• Alfred Wegener's Theory of Continental Drift animation
• Sea floor spreading animation
• Subduction animation

Kilauea: The world's most active volcano

How Volcanoes Work

Sean's Hawaii Photo Gallery

Make your own volcano simulation!

You will need:
1 plastic cup
Modelling clay
1.5 tablespoons of baking soda
1 cup of vinegar
red or orange food coloring
1 spoon
1 gravel surface or non-stainable surface
Paper towels for clean-up
For extra cool points, add walnut pieces or marshmallows, or any other small "pulvarized rock" that will float in vinegar
Adult supervision

To make your volcano:

1. Set the plastic cup upright. Pack modelling clay around cup in an inverted cone shape, so that it is shaped like a volcano or mountain. Be sure to leave the top of the cup open and unobscured by clay, so that "lava" can escape.
2. With adult supervision, drop baking soda (and walnuts or marshmallows if you're extra cool) into bottom of cup in the "magma chamber."
3. Place 1-3 drops food coloring in vinegar, acheiving desired "lava" color. Stir with spoon.
4. Take your volcano sculpture and vinegar solution out to a gravel driveway, where staining and spilling will not be an issue. Put down volcano on gravel, with open end of the cup upright. Do not spill contents.
5. Get ready! Here comes the eruption! Carefully and quickly pour vinegar solution into cup/"magma chamber."
6. The baking soda and vinegar will react chemically, foaming up and over the edge of the volcano sculpture. Watch where the "lava" chooses to flow. It flows most quickly down the steepest slopes and slows down when it hits a flatter surface, such as your driveway.

Volcanology of Hawai'i

Introduction

The Hawai'ian islands are some of the most beautiful places on Earth. Tourists, geologists, biologists, and astronomers congregate there to dive, to study, to conduct research--or just to relax on the powder-soft sand beaches.

Of course, as tourists bask in the clear sunlight, being washed by cool breezes, the first question in their minds is always, "Where did these islands come from? How did they form? Were they always this nice and peaceful?"

No, of course they don't ask that. Waikiki beach is blanketed by bronzed bodies entirely preoccupied with other matters. Some may be aware that they are lying on the edge of a volcano that has been active, spitting to the surface of the Pacific for 70 million years (Hawai'i Volcanoes... Home), but most don't particularly care. That's okay. Pele--the goddess of the Hawai'ian volcanic islands--does not need them to care. She will go on erupting either way.

Geologic Processes: Volcanoes

What is a volcano? A volcano is a vent in the Earth's crust from which melted, plasticky rock from inside the Earth (in the mantle) erupts onto Earth's surface. What we are most familiar with seeing is the mountain that often forms at such a vent because the spewed melt accumulates on the surface as solidified lava--volcanic rock (Marshak G-22).Volcanoes usually form in areas of seismic activity, such as tectonic plate boundaries, mid-ocean ridges, and hot spots (Hines 3).

What kinds of volcanoes are there? There are three types of volcanoes. A sheild volcano is created by silica-poor, basaltic lava flows that are liquid and ropy, called pahoehoe. These formations are usually relatively wide and have gentle slopes because fluid pahoehoe can travel long distances quickly before freezing (Hines 3). The second type of volcano is a cinder cone. These tend to be smaller. Cinder cones are built from pyroclastics, an igneous rock type composed of fragments of rock that combine together and are ejected during an eruption (Hines 3). The name "cinder cone" is appropriate because the volcano is a cone-shaped pile of tephra (Marshak G-3). The third type of volcano is a composite cone, "formed from a combination of both lava flow and pyroclastic materials" (Hines 3).

Are there different kinds of melts? Yes. They are termed differently according to whether or not they have come into contact with Earth's atmosphere. In other words, whether they have come to the surface or not. If a melt is below Earth's surface, it is called magma. If it is in contact with the atmosphere on the surface, it is called lava. The two collectively are termed melts.

So, when you watch a volcano erupt, you are looking at lava. You will never see magma. If you ever dug deep enough to get close to it, you would die. And even then, the hole you dug contains atmosphere, which would touch the magma, thus changing it to lava. You will never see magma.

Lava takes a couple different forms as it travels over Earth's surface after eruption. Native Hawai'ians named the two forms pahoehoe and aa. The two are composed of exactly the same stuff, but appear different because of a temperature difference at different distances from the eruption site.

• Pahoehoe (pa-ho-ay-ho-ay) is ropy, smooth, liquidy lava that flows fast in "ribbon cascades down the mountain" (Jaggar 393). When it cools quickly, it solidifies with a vitreous, or glassy, surface (Jaggar 393). It is form of lava that people usually see pictures of, because it is pretty.
  A helpful visual image: hot, creamy peanut butter on a slope

• Aa (AH-AH) is less hot than pahoehoe and is rougher because cooling causes crystallization to begin. (Melted rock wants to solidify in relatively low temperature, low pressure situations on the surface.) It flows relatively slowly because of its chunkiness. It is easy to remember the name "aa" because when you walk on solid aa with no shoes on, you will say "aa!"
  A helpful visual image: warm, super-chunky peanut butter on a slope

The transition from pahoehoe to aa:
"A quarter mile away [from the volcano] these [lava] torrents change from ropy, wrinkling, and blanketed vitreous upper sufaces to a different type of crusting that starts with granules or nodes of black or rusty red crystalline sprouting and spreads through the mass to an appearance like a bed of hot coals. ... The higher wrinkling type of lava is pahoehoe, the lower sprouting type is aa..." (Jaggar 393).

Are there different kinds of eruptions? Yes. Eruptions differ according to temperature, pressure, and composition of the melt. An eruption can be gentle, squirting ropy lava into the air and creating rivers of lava. Kilauea volcano on Hawai'i Island is a good example of that kind of eruption. Or, an eruption can be extremely explosive, such as the eruption of Mount St. Helens in the 1980s that pulverized one entire side of the mountain. These explosions can be very violent and dangerous.

There are some general rules for eruption types:

All of the volcanoes that make up the Hawai'ian Islands do not erupt violently.

How do volcanic islands form at a hot spot? The Hawai'ian islands represent an anomaly in the Theory of Plate Tectonics. They formed over a hot spot. A hot spot volcano is "An isolated volcano not caused by movement at a plate boundary, but rather by the melting of a mantle plume" (Marshak G-10).

Map of Hawai'ian Islands

Notice that the Hawai'ian Islands are a chain of islands that arc upward from southeast east to west (Marshak 71 Figure 2.48). At first glance, it may appear that the hot spot itself moved, spitting up islands as it went, but that is not the case. A hot spot will always remain fixed where it is, because mantle plumes--tubelike columns of melt, often causing hot spots, that rise from the innermost part of the mantle up to fissures in the crust--do not change location (Marshak 70). Rather than the hot spot moving, the tectonic plate overlying it moves along as normal, pushed by the cycle of crust creation at a mid-ocean ridge and destruction at a subduction zone. While the tectonic plate scoots along at an average of 15 centimeters per year, "...the volcano is carried off the hot spot; then it dies (goes extinct), and a new volcano forms above the hot spot. As the process continues, a chain of extinct volcanoes develops, with the oldest one farthest from the hot spot. The extinct volcanoes gradually [weather, erode, and] sink below sea level and become seamounts" (Marshak 71 Figure 2.48a).

Be sure to watch this hot spot island formation animation (click "View animation").

The hot spot tracks associated with the Hawai'ian Islands extend all the way from the Aleutian Trench south-southeast to Midway Island, southeast-east to the Island of Hawai'i and the newest, unborn Hawai'ian island, Loihi. The tracks created before Midway Island are known as the Emperor seamount chain (Marshak 71).

The Hawai'ian Islands that presently poke above sea level and are recognized as the state of Hawai'i are:

• Kaua'i
• Oahu
• Moloka'i and Lana'i
• Maui
• Kahoolawe
• Hawai'i

Today, the Island of Hawai'i is the only Hawai'ian Island above sea level that is volcanically active. Five volcanoes--Kohala, Hualalai, Mauna Kea, Mauna Loa, and Kilauea--compose the island. Kilauea is perhaps the most active volcano in the world, having been continuously erupting since January 1983.

Other examples of hot spots:

• Iceland
• Bermuda
• Yellowstone
• Easter Island
• Galapagos

Products of Hawai'ian Volcanoes

Ingeous rock types created by Hawai'ian volcanoes:

• basalts
• gabbros
• obsidians
• scoria

No felsic igneous rocks are created, because Hawai'ian melts contain very little silica. Igneous rocks NOT created by Hawai'ian volcanoes:

• granite
• rhyolite
• felsic obsidian
• pumice

• Calcium-rich plagioclase
• olivine
• pyroxine
• amphibole
• some K-feldspar, biotite, pyroxene, quartz, Calcium and Sodium Plagioclase

Mafic igneous rocks, such as the ones found on Hawai'ian Islands,

• can create black sand beaches, and green sand beaches (green because of olivine crystals.)
• weather to red dirt because of oxidizing iron
• include aa with lots of air passing through, creating breathing rocks at Sharks Cove
• aa flows (such as the ones seen at sharks cove on Oahu) and pahoehoe flows (such as the ones seen at Kilauea on Hawai'i)

The older islands are presently covered in vegetation, while the new islands still have exposed, fresh lava flows and exposed sedimentary coasts, such as the ones along the road North of Koko Crater on Oahu.

All the islands have volcanic craters. Craters on Oahu include Hanauma Bay, Koko Crater, Diamond Head, and Punchbowl Crater.

Literature Cited

Brigham, William T. Notes on the Volcanoes of the Hawaiian Islands with a History of Their Various Eruptions. Cambridge: Riverside Press. 1868.

-----. The Volcanoes of Kilauea and Mauna Loa on the Island of Hawaii: Their Variously Recorded History to the Present Time. Honolulu: Bishop Museum Press. 1909.

Earlham College. Earlham Geosciences Dept. Physical Geology Laboratory 2: Igneous Rocks Identification. Richmond, Indiana, 2004.

Hawai'i Volcanoes National Park: Home. 19 April 2004. Hawai'i Volcanoes National Park. 1 April 2004. <http://www.nps.gov/havo/home.htm>

Hines, Eric. Quick Study Academic: Earth Science. Boca Raton, Florida: BarCharts, Inc. Oct. 2001.

Jaggar, T.A. The Geological Society of America: Memoir 21: Origin and Development of Craters. Baltimore, MD: Waverly Press, Inc. 1947.

Kerr, Richard A. "High-Tech Fingers on Earth's Erratic Pulse." Science 299.5615 (28 March 2003): 2016.

Marshak, Stephen. Essentials of Geology. New York: W. W. Norton & Company, Inc. 2004.

Stone, Richard. "Stalking Nature's Most Dangerous Beasts." Science 299.5615 (28 March 2003): 2015.

Link to other Student Webpages for 2004 Earlham Physical Geology

Copyright © 2004 Earlham College. Revised April 20, 2004 . Send corrections or comments to bestan@earlham.edu