Different Types of Volcanoes and Lava: Worksheet Answer Key
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Volcanoes fall into four main types — Hawaiian, Strombolian, Vesuvian, and Peléan — distinguished chiefly by how fluid their lava is and how violently they release gas, ash, and solid debris. The thinner the lava, the calmer the eruption; the more viscous the lava, the more explosive and destructive the volcano becomes.
What are the main types of volcanoes?
The main types of volcanoes are classified by the character of their eruptions and the viscosity of their lava. Each type marks a step along a scale that runs from quiet outpourings of liquid lava to catastrophic explosions.
- Hawaiian type. These volcanoes show no significant release of vapors and gases; their lava is fluid.
- Strombolian type. The lava is also fluid, but these volcanoes release large amounts of vapors and gases while producing no ash; on cooling, the lava becomes wavy.
- Vesuvian type is marked by more viscous lava, with abundant emissions of vapors, gases, volcanic ash, and other solid eruptive products. On cooling, the lava becomes blocky.
- Peléan type. Extremely viscous lava produces violent explosions that throw out scorching gases, ash, and other material in the form of burning clouds that destroy everything in their path.
What is the Hawaiian type of volcano?
Hawaiian-type volcanoes calmly and abundantly pour out nothing but fluid lava during an eruption. The volcanoes of the Hawaiian Islands are the classic example. The Hawaiian volcanoes, whose bases lie on the ocean floor at a depth of roughly 4,600 meters, undoubtedly formed as a result of powerful submarine eruptions.
The force of these eruptions can be judged from the fact that the absolute height of the extinct volcano Mauna Kea (meaning "white mountain") reaches 8,828 meters from the ocean floor (its relative height is 4,228 meters). The best known are Mauna Loa, otherwise "high mountain" (4,168 meters), and Kīlauea (1,231 meters).
Kīlauea has an enormous crater — 5.6 kilometers long and 2 kilometers wide. On its floor, at a depth of 300 meters, lies a churning lava lake. During eruptions, mighty lava fountains form on it, reaching heights of up to 280 meters with a diameter of about 30 meters.
Droplets of fluid lava thrown to such a height are drawn out in the air into thin threads that the native population calls "Pele's hair" — after Pele, the fire goddess of the ancient inhabitants of the Hawaiian Islands. The lava flows during the eruption of Kīlauea sometimes reached enormous size — up to 60 kilometers in length, 25 kilometers in width, and 10 meters in thickness.
What is the Strombolian type of volcano?
Strombolian-type volcanoes release mainly only gaseous products. An example is the volcano Stromboli (900 meters high) on one of the Lipari Islands (north of the Strait of Messina, between the island of Sicily and the Apennine Peninsula).
At night the reflection of Stromboli's fiery vent in the column of vapors and gases, clearly visible at distances of up to 150 kilometers, serves sailors as a natural lighthouse. Another natural lighthouse is widely known among sailors all over the world — the volcano Izalco in Central America, off the coast of El Salvador.
Punctually, every 8 minutes, Izalco throws up a column of smoke and ash that rises 300 meters. Against the dark tropical sky it is strikingly lit by the crimson glow of the lava.
What is the Vesuvian type of volcano?
The fullest picture of an eruption is given by volcanoes of the Vesuvius type. An eruption is usually preceded by a strong subterranean rumble accompanying earthquake shocks and tremors. Suffocating gases begin to escape from fissures on the volcano's slopes. The release of gaseous products — water vapor and various gases (carbon dioxide, sulfur dioxide, hydrogen chloride, hydrogen sulfide, and many others) — intensifies.
They escape not only through the crater but also from fumaroles (fumarole derives from the Italian word "fumo" — smoke). Clouds of steam, together with volcanic ash, rise several kilometers into the atmosphere. Masses of light-gray or black volcanic ash, consisting of the tiniest fragments of congealed lava, are carried thousands of kilometers.
The ash of Vesuvius, for instance, reaches as far as Constantinople and North America. Black clouds of ash shroud the sun, turning bright day into dark night. The strong electrical charge produced by the friction of ash particles and vapors shows itself in electrical discharges and claps of thunder. Vapors lifted to a great height condense into clouds from which, instead of rain, torrents of mud pour down.
From the volcano's vent come volcanic sand, stones of various sizes, and volcanic bombs — rounded lumps of lava that solidify in the air. Finally lava appears from the vent and rushes down the mountainside in a fiery stream.
A volcano of the same type — Klyuchevskaya Sopka
Here is how the picture of an eruption of this type — Klyuchevskaya Sopka on October 6, 1737 (more details: A description of the volcanoes of our continent) — was conveyed by the first Russian explorer of Kamchatka, Academician S. P. Krasheninnikov (1713–1755). He took part in the Kamchatka expedition while still a student of the Russian Academy of Sciences in 1737–1741.
The whole mountain seemed a red-hot stone. The flame, visible inside it through the crevices, sometimes rushed downward like fiery rivers with a terrible roar. Within the mountain could be heard thunder, crackling, and as if a blowing by powerful bellows, from which all the nearby places trembled.
An unforgettable picture of an eruption of the same volcano on the night of the New Year of 1945 is given by a modern observer:
A sharp orange-yellow cone of flame, a kilometer and a half high, seemed to pierce the clouds of gases that rose in an enormous mass from the volcano's crater to about 7,000 meters. From the top of the fiery cone, red-hot volcanic bombs fell in a continuous stream. There were so many of them that they gave the impression of a fairy-tale fiery blizzard.
The illustration shows samples of various volcanic bombs — these are clots of lava that have taken on a definite shape. They acquire a rounded or spindle-shaped form by rotating during flight.
- A spherical volcanic bomb — a sample from Vesuvius;
- Trass — a porous trachytic tuff — a sample from the Eifel, Germany;
- A spindle-shaped volcanic bomb — a sample from Vesuvius;
- Lapilli — small volcanic bombs;
- A volcanic bomb covered with a crust — a sample from southern France.
What is the Peléan type of volcano?
The Peléan type of volcano presents an even more terrible picture. As a result of a frightful explosion, a significant part of the cone is suddenly pulverized in the air, blanketing the sunlight in an impenetrable gloom. Such was the eruption of the Mont Pelée volcano.
The Bandai-San volcano
The Japanese volcano Bandai-San also belongs to this type. For more than a thousand years it was considered extinct, and then suddenly, in 1888, a significant part of its cone, 670 meters high, was blown into the air.
The volcano's awakening from its long repose was terrible:
The blast wave tore trees up by the roots and caused dreadful destruction. The pulverized rock hung in a dense shroud in the atmosphere for 8 hours, blocking out the sun, and bright day gave way to dark night... No outpouring of fluid lava occurred.
Eruptions of this kind among Peléan-type volcanoes are explained by the presence of very viscous lava, which prevents the release of the vapors and gases that have accumulated beneath it.
What are rudimentary forms of volcanoes?
Besides the types listed above, there are rudimentary forms of volcanoes, in which the eruption was limited to a breakthrough of only vapors and gases to the earth's surface. These rudimentary volcanoes, called "maars," are found in western Germany near the Eifel region.
Their craters are usually filled with water, and in this respect maars resemble lakes surrounded by a low rim of rock fragments thrown out by the volcanic explosion. Rock fragments also fill the floor of a maar, and deeper down ancient lava begins.
The richest diamond deposits in South Africa, located in ancient volcanic channels, appear by their nature to be formations similar to maars.
What types of lava are there?
By their silica content, lavas are divided into acidic and basic. In the former, the amount reaches up to 76%, while in the latter it does not exceed 52%. This chemical difference governs the lava's color, weight, and how freely it flows.
Acidic lavas are distinguished by a light color and low specific gravity. They are rich in vapors and gases, viscous, and sluggish. On cooling, they form what is called blocky lava.
Basic lavas, on the contrary, are dark in color, easily fusible, poor in gases, highly mobile, and of considerable specific gravity. On cooling they are called "wavy lavas."
What is the lava of Vesuvius like?
In chemical composition, lava differs not only between volcanoes of different types but also within one and the same volcano, depending on the periods of eruption. For example, Vesuvius at present pours out light (acidic) trachytic lavas, while the more ancient part of the volcano, the so-called Somma, is built up of heavy basaltic lavas.
How fast does lava move?
The average speed of lava movement is five kilometers per hour, but in individual cases fluid lava has moved at a speed of 30 kilometers per hour. Once it has poured out, lava soon cools and a dense, slag-like crust forms on it. Owing to the poor thermal conductivity of lava, one can readily walk on it, as on the ice of a frozen river, even while the lava flow is in motion.
Inside, however, the lava long retains a high temperature: metal rods lowered into the fissures of a cooling lava flow quickly melt. Beneath the outer crust, slow movement of the lava continues for a long time — it was noted in a flow 65 years old, while traces of heat were established in one case even 87 years after the eruption.
What temperature does a lava flow reach?
The lava of Vesuvius, seven years after the eruption of 1858, still held a temperature of 72°. The initial temperature of the lava was determined for Vesuvius at 800–1,000°, and the lava of the Kīlauea crater (Hawaiian Islands) at 1,200°. In this connection it is interesting to learn how two research workers of the Kamchatka Volcanological Station measured the temperature of a lava flow.
In order to carry out the necessary research, they leapt, at the risk of their lives, onto the moving crust of a lava flow. On their feet were asbestos boots, which conduct heat poorly. Although it was a cold November and a strong wind was blowing, even in the asbestos boots their feet still grew so hot that they had to stand alternately on one foot and then the other so that the sole could cool down at least a little. The temperature of the lava crust reached 300°. The brave researchers went on working. At last they managed to break through the crust and measure the temperature of the lava: at a depth of 40 centimeters from the surface it was 870°. Having measured the temperature of the lava and taken a sample of gas, they safely leapt onto the solidified edge of the lava flow.
Thanks to the poor thermal conductivity of the lava crust, the air temperature above a lava flow changes so slightly that trees continue to grow and bloom even on small islets bordered by branches of a fresh lava flow.
The outpouring of lava takes place not only through volcanoes but also through deep fissures in the earth's crust. In Iceland there are lava flows that have congealed between layers of snow or ice. Lava filling the fissures and cavities of the earth's crust can retain its temperature for many hundreds of years, which explains the presence of hot springs in volcanic regions.
