Throughout history people have a way of telling stories to try to explain why things happen. One story began many hundreds of years ago when the Romans began to wonder about volcanoes and why they erupted. They began to make up stories to explain this natural event. The Romans believed a God named Vulcan worked deep in the Earth’s crust making swords and armor for the other Gods. When Vulcan would become upset, he would explode! Other cultures also had stories to explain this eruption. The Hawaiians believed that a Goddess of Fire, Pele was living with her sister, Namaka, Goddess of the Sea. The two sisters had an argument and Namaka chased Pele from their home. Pele moved to a different island and was never pleased. She would have temper tantrums and explode! (Simon, 2006) According to Maori legend, the volcanoes around Lake Taupo in New Zealand were powerful giants that fought for the love of a female mountain, hurling hot rock and fire at each other to win her love! (Rooney, 2006)
I will have my students in their writing period make up stories to explain volcanic eruptions.
Today we now know how volcanoes erupt and how they are formed. A volcano is a term used to describe when hot molten rock or lava erupts from the Earth’s surface. The volcano erupts when pressure builds up deep inside the Earth. Melted rocks, called magma, flow up through a vent or crack in the Earth’s surface very quickly. This magma is flowing sometimes very slowly or sometimes very quickly. It then flows as lava out of the volcano, ash, steam, rock and dust blows out of the crack or hole and enters the Earth’s air. Convection is the way that the heat energy is transferred into gases and liquids. When the gas or liquid is heated the part closest to the heat source expands, becomes less dense and rises. The cooler and denser liquid sinks down. Convection currents carry ash from volcanoes up into the air. So now that we know that a volcano is an opening in the Earth where hot liquid rock called magma bursts out of, we need to examine the Earth’s crust to see what causes these cracks. (Watts, 1996)
The Earth is made of four layers. The layers are the inner core, the outer core, the mantle and the crust. The Earth has a solid crust. The crust is between three miles thick to 43 miles thick. The crust area that is three miles (5 km) is the Oceanic Crust. The Oceanic Crust or ocean floor is made up of heavy rocks such as basalt and dolerite. The second crust or Continental Crust is between 19-37 miles (30-60 km) thick. This crust makes up mountains, hills, landforms and is mostly made of lighter rocks such as granite, sandstone and limestone. There are various layers of rock within our crust. The first layer is Sedimentary Rock. The second layer is Metamorphic Rock, then Igneous Rock and deep in the crust, Melted Rock. The students in third grade also participate in a rock science unit so information about these rocks will be beneficial. (Moores, 1995)
The mantle is located below the crust. It is 1,789 miles thick (2,885 km). Within the mantle of the Earth are thin layers. They are mostly solid rock and small amounts of molten rock called magma. The Earth’s layer or crust is always moving. The areas of the Earth are divided into plates. There are seven main plates, and many small plates. (Moores, 1995)
The outer core of the Earth is 1,407 miles (2,270 km) thick and is made up of liquid iron and nickel. The inner core is 754 miles thick (1,216 km) and is 3,950 miles (6,371 km) down to the center of the Earth. The internal temperature is a very hot 5,432 F (3,000 C) at the core. With all this heat and then cooling no wonder the Earth’s is in constant motion and undergoes eruption! So where and why do these eruptions occur? (Moores, 1995)
Volcanic eruption occurs most often in the area of the Earth we call the Ring of Fire. This area encircles the Pacific Ocean. The Pacific Ring of Fire is the name that scientists use to describe the area around the Pacific Ocean. This area has many volcanic eruptions and also earthquakes. Most of the volcanic eruptions occur in this area although volcanoes do erupt in other areas. The lithosphere or the two layers of solid rock made up of the upper mantle and the crust fit together like a puzzle. The volcanoes that erupt build islands, such as Hawaii, mountains, plains, lakes and the ocean floor. Imagine when the pieces collide together, hot melted magma erupts through the crack. We can not feel it but the earth is in constant motion. The plates push and pull at a rate of 3/4-8 inches (2-20 cm) a year. Sometimes the plates collide into each other. Imagine when the pieces collide together, hot melted magma erupts through the crack. When the plates push apart, magma from the mantle erupts and creates a new ocean crust. When the plates move together they form mountains. The area where these plates slide on top of one another is where the most earthquakes and volcanoes occur. It is called the Ring of Fire. (Adams, 2001)
The outer part of the Earth or lithosphere is the source of all volcanic eruptions. There are six major plates and many smaller plates. They consist of oceanic or continental plates. The plates under the ocean are about 70-80 km or 40-50 miles thick and the plates under the continents are 100-150 km or 60-90 miles think. The plates as discussed previously are in constant motion. They either slide into one another or they pull away from each other. Intense earthquakes and volcanoes occur during this movement. The plates are spreading apart, colliding into one another, subducting or one sliding down and the other plate moving on top and sliding by one another or transforming like the faults.
These movements occur in the ocean and on land. An ocean to ocean movement is when two plates within the Earths crust move and one plate subducts or moves down under the other plate. This movement forms an island volcano. Over millions of years, the volcanic eruptions that occur under water produce islands such as Japan and Philippines. The magma then rises to the surface and forms a volcano line. This is where mountains and volcanoes are formed. (Adams, 2001)
There are basic parts of a volcano. The crater is the depression at the summit of a volcano, connected by a vent or pipe to the magma chamber below. The caldera is a crater more than 1 km in diameter formed by the summit of a volcano when lava is drained from an underground magma chamber, causing the summit to be unsupported and collapse. A pit crater is a collapsed feature on the flank or summit of a volcano that is smaller than the main caldera at the summit of a volcano. The vent is a pipe like conduit from the magma chamber to the surface. There is also a secondary vent called the fumaroles that emits steam and gas. (http://library.thinkquest.org )
Additional activities:
Students would benefit from viewing a picture of the Pacific Ocean and the Ring of Fire on a map. Enchanted Learning has numerous pictures for students to view. Students would benefit from a visual map of the world to locate islands. Next the students should picture a thin ocean plate meeting a thicker continental plate. They should picture the thin ocean plate subducting or sinking down. Have the students imagine living on a beautiful island with all the wonderful landscape. Have them picture the waves, the tides and the lovely ocean air. Now tell them they may be standing on a volcano! I will have the students imagine objects smashing into each other. This outer layer is like a jigsaw puzzle in motion. One piece of the puzzle smashes into the other causing one puzzle to lift up on top of the other.
Continental Plates or Tectonic Plates
The highest place on Earth is Mount Everest in the Himalayas. Yet at the height of 29,035 feet above sea level lie rocks and fossil from the ocean floor. How did this occur? Scientists have been working on this phenomenon for many years. The formation of this mountain and others begins when the Earths’ plates collided into each other. Over time, this movement formed Mount Everest and all of our landforms. (Sands, 2004)
We did not understand this information about plate movement until in 1915 when a German Scientist named Alfred Wegener proposed the notion that our continents moved and have been moving for millions of years. He thought that the continents were plowing though the oceanic crust like ships through ice. At first many people and scientists thought his idea was mistaken, and besides the similarity in the rocks and plants of South America and Africa, he had no other evidence to prove his hypothesis. Many years later, scientists proved him right by discovering that the tectonic plates were indeed moving. The name given to our old world was Pangaea or Permian Period. This land shape took place a few years ago; 290 mya (million years ago!) Students should view a pictorial to observe the differences from the Permian Period to the Triassic Period, to the Jurassic Period then Cretaceous Period and finally to the Present day. Have the students identify various continents and observe their movement. So our continents are really in constant movement! (Sands, 2004)
Oceanic: All Aboard!
Volcanoes occur on the Earth’s continents and under the ocean floor. The Pacific Ocean is over 64 million square miles. That is very large! We can only see the beautiful water and waves, but under ground the ocean floor has volcanoes, mountains, hills, and valleys. The Pacific Ocean has some of the longest mountain ranges of the world. These island volcanoes have erupted for over 75 million years. Many are now extinct. They have eroded, leaving coral reef. When these mountains peak through the surface of the water, it is a volcanic island or hotspot volcano. First a volcano at the bottom of the ocean erupts. Hot lava flows into the sea. The layers pile up and sides of the volcano thicken as the lava cools. The lava cools quickly because of the cool temperature of the water. The volcano erupts often and grows higher and higher. Finally the top of the volcano rises above the surface of the water. Now an island has formed. Beautiful Hawaiian Islands and Iceland were formed this way. Mauna Loa in Hawaii is the Earth’s largest volcano. Most of its shape is concealed under the ocean, approximately 90%! Mauna Loa is also capable of producing 5 million tones of lava an hour!
Types of Volcanoes
If you look carefully at a mountain, lake or any land form, they all look different. Volcanoes also look different and erupt in different ways. There are many types or groups of volcanoes but the students in my classroom will concentrate on four of the most common types. Each type of volcano will have a group of students and after their research about volcanoes is complete, they will make a volcano of that type. There are
Shield
Volcanoes,
Cinder Cone Volcanoes,
Stratovolcanoes or Composite Volcanoes
and
Dome Volcanoes.
For this section of the unit the student should have a visual picture of each volcano type. NASA websites and also NOVA.com have pictures of these types of volcanoes. (Abbott, 2006)
Shield Volcano
A gently-sloping volcano that emits mostly basaltic lava (very fluid lava) that flows in long-lasting, relatively gentle eruptions. Explosions are minimal. Shield volcanoes can be very big. They are the largest volcanoes on Earth that actually look like the typical volcano we all visualize. Shield volcanoes are mostly basalt which is a type of lava that is very fluid when it erupts. The gentle slopes look like an ancient warrior’s shield. That is were it gets its name. The gentle slope causes the flow to run easily and therefore there is no pile up. Water somehow gets into the volcanoes vent and due to the water the eruption is very explosive for only at the first few minutes, then later it is non-explosive. An example of a shield volcano is Kilauea in Hawaii and also Mauna Loa which is the world’s largest volcano!
Cinder Cone Volcano
A cone-shaped volcano, also called a scoria cone, whose steep sides are formed by loose, fragmented cinders that fall to the Earth close to the vent. They are the simplest volcanoes because they are built from particles and blobs of congealed lava ejected from a single vent. As the gas charged-lava flows through a single vent, that usually only rises up to about 1,000 feet tall. There is usually a bowl-shaped crater at the top. The gas-filled lava erupts into the air, the lava fragments into pieces. These pieces form cinders and so it gets its name from these cinder shapes. Pacaya volcano in Guatemala, Central America has many eruptions. Cinder Cone Volcanoes are also located in western North America and in the Andes, Mountains of Peru. El Mish is an active cinder volcano.
Stratovolcano
Also called Composite Volcanoes. The Composite Volcanoes are the most familiar. They are tall, symmetrical and are commonly steep-slide or slope steeply toward a small crater. They are usually formed by multiply, violent and tall eruptions which add to the height of the volcano. The first initial explosion is very violent and produces very little or even no lava flow but lots of ash. That eruption is followed by huge plinian eruption that puts out lots and lots of ash. There are more composite or stratovolcanoes in the world then any other kind of volcano. Mount Shasta in California and Mt. St. Helens in Washington State are good examples of this type of volcano. Students would benefit from watching a video of the Mt. St. Helen’s eruption. Both are still considered active volcanoes even though they have not erupted in a long time. A steep-coned volcano explosively emits gases, ash, pumice, and a small amount of stiff, silica lava (called rhyolite). This type of volcano can have eruptions accompanied by lahars deadly mudflows. Stratovolcanoes kill more people than any other type of volcanoes. This is because of their abundance on Earth and their powerful mudflows, pyroclastic rock and ash. About 60% of the Earth’s volcanoes are Stratovolcanoes.
Dome Volcano
This volcano has thick, slow-moving lava that forms a steep-sided dome. It gets its name from the dome shape. It is also called an Acid. Eruptions are characterized by viscous lava explosions which allow lava to flow for great distance and spill over and around the vent. The increase in temperature causes the dome to expand while the outer lava cools. This growth causes the newly hardened surface to splinter, causing loose debris to fall from its sides. This appearance is the reason for its name.
After a dome volcano erupts, it may become plugged with hardening lava. The plugged vent does not allow the gas to escape and as the pressure builds, the volcano explodes again as in the case of Mono Dome in California after it’s most recent explosion. There are numerous dome volcanoes in Japan. This dome volcano oozes thick lava like the toothpaste from the tube experiment the students will participate in.
Types of Lava
The two most important properties of lava are its viscosity and the amount of gas dissolved in the liquid rock. There are three types of lava flow; Pillow, Pahoehoe, and Aa. Pillow flows are the most common and occur under the ocean. The lava forms large blobs and the underwater lava hardens. Pahoehoe lava means “smooth, unbroken lava”in Hawaiian. It is thin and has a smooth flow, mostly ropey flows. There is a small volume of hot, fluid basalt. When it solidifies the content is of a smooth surface. Aa means “stony with rough lava”. The flow is of viscous magma and when it solidifies it is rough or rubbery and composed of broken lava blocks. (www.volcano.und.edu.com )
Size and Types of Eruption
There are four steps or events that occur during an eruption. First melted rock moves from deep inside the Earth toward the volcano crater. Next super hot gas rises in front of the melted rock. As the melted rock comes closer to the crater, gas escapes. Students can visualize bubbles from a soft drink or soda bottle. As the gas escapes the volcano begins to erupt. Last the melted rock pushes out of the vent in the volcano. Have the students visualize the smooth flow of honey being squeezed out of a honey bottle. Now have them visualize the honey bottle clogged up with dirt, rocks, and soil. You keep squeezing the bottle as hard as you can and then, there is a very large eruption with the honey exploding everywhere!
Lava flow also differs. It is named after how it looks as it cools and hardens. Pillow lava is the most common. This form is found along the mid-ocean ridge where volcanoes ooze pillow-shaped lumps of lava through the ocean floor crack. Sometimes Pillow lava can be found on dry land that was once part of the ocean floor. (Moores, 1995)
Pahoehoe lava is runny, thin and has a very fast moving flow that is smooth. They are often formed by small volumes of hot fluid basalt. The surface of Pahoehoe lava cools quickly and forms a thin smooth skin like shape, similar to a rope. They may embrace obstacles at a rate of 50 m. an hour. Underneath the surface the lava still flows because it has not cooled yet. When the lava flow finally cools, it solidifies to a smooth surface. (Moores, 1995)
Aa lava flow moves more slowly and is not as hot as Pahoehoe lava. Aa are emitted from the vent at high rates ranging from and up to 50 km. an hour. Aa is a viscous magma and has animated bursts of energy. They may bush down houses, wall and forests. When Aa lava cools and solidifies, it forms chunks of rocks, some being very thick and rough. (Moores, 1995)
Students can discuss the three different lava flows and decide if they lived near a volcano which type of lava flow they would prefer and why. Have the students imagine lava stopping short of their town as in the Mt Etna in Sicily, Italy eruption. The lava flow stopped short of destroying thousands of homes and then have them visualize Pompeii where the enter village was destroyed and buried.
The biggest volcanic eruption recorded took place on August 27, 1883 in Indonesia. When Krakatau Volcano erupted, it killed over 36,000 people and destroyed over 160 villages. The explosion was over 25 times as powerful as a hydrogen bomb! The deadliest volcano, Tambora, also occurred in Indonesia in 1815. The gas and lava flow killed over 92,000 people. The largest volcano is located in Hawaii’s Mauna kea. It is 33,000 feet tall from base to summit. Mount Everest in 29,000 feet tall and at ground level appears taller than Mauna kea. Some of Mauna kea is under the ocean so it appears to be shorter in size. (Sands, 1996)
Other facts about volcanoes that the students will be interested in are:
-
· The ash from Mount St. Helen’s eruption flew up twelve (12) miles into the air!
-
· In 1883 Krakatoe erupted and was heard over 3,000 miles away!
-
· In Hawaii, Kilauea lava was thrown 2,000 feet into the air!
-
· Molten lava temperature is 4,000 degree Fahrenheit which is twelve (12) times hotter than boiling water! That’s HOT! (www.northern-stars.com)
-
· In 1815 Mt. Tambora, Indonesia ejection of 30 km3 of volcanic debris causing a “year with no summer”. Earth temperature dropped due to the ash blocking the incoming sunlight.
-
· Indonesia has the most volcanoes.
-
· United States has about 40 volcanoes in the lower 48 States; however Alaska has over 60 volcanoes!
-
· 5000 BC Mt. Mazama, Oregon explosion ejected 40 km3 of debris and then collapsed in form of a caldera. It is now filled with water and is called Crater Lake!
Types or styles of eruptions are named after volcanoes. The eruption variability depends on the magma composition, the amount of water present and the volcano type. The types are Strombolian, Vulcanian, Pelean (Peleean), Hawaiian and Plinian. The Plinian eruption is the most dangerous and the most explosive! Before discussing the types of eruptions, students can view a pictorial image of each type of eruption to understand the difference at www.geology.sdsu.edu/how_volcanoes_work.com . The eruptions are listed from the smallest eruption to the largest.
Hawaiian
This eruption is considered the smallest or calmest with large amounts of runny lava. The eruptions are highly fluid basalt lava in nature with low gas content and a thin lava flow. These eruptions come out of Shield volcanoes. The eruptions are about 2 km in height. Hawaiian eruptions are named after the volcanoes in Hawaii.
Strombolian
This eruption is considered small but varies to a high eruption with small sticky lava bombs, blocks, ash and gas. The eruption has a nickname of “Lighthouse of the Mediterranean”because of the Stromboli eruptions that occur between Italy and Sicily. The eruptions are short lived with a pasty lava flow with the eruption blasting tens or hundreds meter into the air. The eruption can be viscous in basaltic lava erupting from the throat of the volcano, with a high gas pressure and booming blast. Even though this eruption is noisier than a Hawaiian eruption it is not more dangerous. The eruptions are about 10 km in height. This eruption occurs in the stratovolcanoes such as Mt. Etna.
Vulcanian
This is more explosive than the Stromolian due to the magma and rocks plugging the vents. There is large gas pressure and build up so a large eruption occurs with a large ash exploding 20 km or higher. These types of eruptions are usually precursors to Plinian eruptions.
Plinian
This explosive eruption in which a steady, turbulent stream of fragmented magma and magmatic gases is released at a high velocity from a vent. Large volumes of tephra and tall eruptions occur. The eruptions are 30 km-55km.
The volcanoes are Active, Dormant or Extinct. An active volcano is erupting or has erupted in resent time. About 20 volcanoes erupt somewhere on Earth every day. It is estimated that between 1,300-1,500 volcanoes have been active during the last 10,000 years. An active volcano is Stomboli in Italy. It has been erupting for possibly 5,000 years! A dormant volcano is active but is considered “sleeping”. It will erupt in the future. In March of 1980, Mount St. Helen awakened from a long sleep! The energy released from this “sleeping” volcano was equal to ten million tons of dynamite! An extinct volcano is expected to never erupt again. Many of these volcanoes are in the Hawaiian Islands. (Simon, 2006)
Have the students discuss which type volcano they would prefer to live near and why. Also have a discussion with them about the fact that some volcanoes are considered “Extinct” but have been known to “Explode”.
