1. List and describe the factors that determine the nature of an igneous eruption.
2. List the categories of materials that may be emitted during a volcanic eruption.
3. Compare and contrast the three basic types of volcanoes (shield, composite, and cinder cone) as to size, shape and eruptive style.
4. Name a prominent example of each of the three basic types of volcanoes.
5. Relate the distribution of volcanic activity to the plate tectonics model.
Mauna Loa Volcano, Hawaii, a shield volcano, as viewed from the summit of Kilauea, about 33 miles to the southeast.
Mauna Loa, on the Big Island of Hawaii, is the largest active volcano in the world. It last erupted in 1984.
Mauna Loa erupted 14 times in the 20th Century, and 37 times since 1832.
Mauna Loa is the most massive mountain on Earth, rising to an elevation of 13,677 feet above sea level, or 31,677 feet above the sea floor.
Its volume is 10,000 miles3.
The tallest mountain on Earth is located nearby, also on the Big Island of Hawaii. It is Mauna Kea, rising to an elevation of 13,796 feet above sea level, or 31,796 feet above the sea floor.
Both Mauna Loa and Mauna Kea are shield volcanoes.
In comparison, Mt. Everest (in the Himalayas), the highest point on Earth above sea level, rises to an elevation of 8848 m (or 29,028 ft). Mt. Everest is NOT a volcano, however.
The largest volcano in the Solar System is located on the planet Mars. Its name is Olympus Mons (or Mount Olympus), and it is three times as high as the largest volcanoes on Earth (nearly 27 km high). It is about 100 times as massive as one of the Hawaiian volcanoes.
Cinder cone, Puu Puai, created by eruption in 1959, Devastation Trail, Kilauea, Hawaii Volcanoes National Park.
The volcano Paracutin, in Mexico, is a well-known example of a cinder cone.
Eruption of Mt. St. Helens
large (1 - 10 km across)
layered structure, consisting of alternating layers of lava and pyroclastic material
high silica content (sialic or intermediate) with composition of andesite, dacite, and occasionally rhyolite
These volcanoes make up the largest perentage of the Earth's volcanoes (about 60%)
Examples: Mt. Vesuvius, Cascade Range volcanoes such as Mt. St. Helens and Mt. Rainier
According to Volcano World, there are six major types of volcanoes:
"Strato volcanoes--making up the largest percentage (~60%) of the Earth's volcanoes, these are characterized by eruptions of cooler and more viscous lavas than basalt. The usual lavas that erupt from strato volcanoes are andesite, dacite, and occasionally rhyolite. These more viscous lavas allow gas pressures to build up to high levels (they are effective "plugs" in the plumbing), therefore these volcanoes often suffer explosive eruptions. They are usually about half-half lava and pyroclastic material, and the layering of these products gives them their other common name of composite volcanoes. Strato volcanoes are commonly found along subduction-related volcanic arcs."(Volcano World, http://volcano.und.nodak.edu/vwdocs/frequent_questions/grp12/question1401.html).
"Large rhyolite caldera complexes--the most explosive of Earth's volcanoes. These are volcanoes that often don't even look like volcanoes. They are usually so explosive when they erupt that they end up collapsing in on themselves rather than building any tall structure. The collapsed depressions are called calderas, and they indicate that the magma chambers associated with the eruptions are huge. Fortunately we haven't had to live through one of these since 83 AD when Taupo erupted. Yellowstone is the most famous US example of one of these. Their origin is still not well-understood. Many folks think that Yellowstone is associated with a hotspot, however, a hotspot association with most other rhyolite calderas doesn't work. " (Volcano World, http://volcano.und.nodak.edu/vwdocs/frequent_questions/grp12/question1401.html).
"Monogenetic fields. These also don't look like a "volcano", rather they are a collection of sometimes hundreds to thousands of separate vents and flows. These are the product of very low supply rates of magma. The supply rate is so slow and spread out that between the times of eruptions the plumbing doesn't stay hot so the next batch of magma doesn't have any preferred pathway to thesurface and it makes its own path. A monogenetic field is kind of like taking a single volcano and spreading all its separate eruptions over a large area. There are a number of monogenetic fields in the American southwest, and there is a famous one in Mexico called the Michoacan-Guanajuato field. "(Volcano World, http://volcano.und.nodak.edu/vwdocs/frequent_questions/grp12/question1401.html).
"Flood basalt provinces--another strange type of "volcano". Some parts of the world are covered by thousands of square kilometers of thick basalt lava flows--some flows are more than 50 meters thick, and individual flows extend for hundreds of kilometers. The old idea was that these flows went whooshing over the countryside at incredible velocities. The new idea is that these flows are emplaced more like pahoehoe flows--slow moving, with most of the great thickness being accomplished by injecting lava into the interior of an initially thin flow. The most famous US example of a flood basalt province is the Columbia River Basalts, covering most of SE Washington State, and extending all the way to the Pacific and into Oregon. The Deccan Traps of NW India are a much larger flood basalt province."(Volcano World, http://volcano.und.nodak.edu/vwdocs/frequent_questions/grp12/question1401.html).
"Mid-ocean ridge volcanism occurs at plate margins where oceanic plates are created. There is a system of mid-ocean ridges more than 70,000 km long that stretches through all the ocean basins--some folks consider this the largest volcano on Earth. Here, the plates are pulled apart by convection in the upper mantle, and basalt lava intrudes to the surface to fill in the space. Or, the basalt intrudes to the surface and pushes the plates apart. Or, better yet, it is a combination of these two processes. Either way, this is how the oceanic plates are created. A recent mid-ocean ridge eruption took place along the Gorda Rise--the mid-ocean ridge that separates the Juan de Fuca plate from the northern part of the Pacific plate. "(Volcano World, http://volcano.und.nodak.edu/vwdocs/frequent_questions/grp12/question1401.html).
Viscosity of the magma controls the type of volcano.
Viscosity is controlled by the composition and temperature of the magma.
Silica (SiO2) content controls viscosity.
Granitic/sialic magma is more viscous (stiffer) than basaltic/mafic magma.
Hotter lavas are less viscous.
(Remember Bowen's Reaction Series and the relative temperatures of sialic vs mafic magmas
Shapes of volcanoes are due to the viscosity of the magma (or lava).
Runny basaltic lava will not form a steep cone; forms relatively flat shield volcanoes.
Mafic lavas are low in silica (only about 50% SiO2)
Sialic lavas may have more than 70% SiO2.
Explosivity of the volcano is also controlled by the viscosity (and chemistry) of the lava or magma.
Gases are easily released from low viscosity (runny) lavas.
Ex. = vesicular basalt.
Looking into Caldera of Kilauea Volcano, which is about 2 to 2.5 miles in diameter, and about 400 feet deep. A road around the crater rim is 11 miles long. Steam is rising from the inner crater, Halema'uma'u, near the center of the left photo.
Kilauea is the world's most active volcano, and it has been erupting continuously since January 3, 1983, with lobes of lava threatening (and destroying) housing subdivisions, and entering the sea through lava tubes.
Kilauea rarely erupts from its summit. Instead it erupts from vents on its flanks, particularly along its east and southwest rift zones.
The summit of Kilauea is about 4000 feet above sea level.
See explanatory diagram of Kilauea caldera on sign at Volcanoes National Park.
Pahoehoe flows (from circa 1993) near Kalapana Black Sand Beach.
Pahoehoe at the end of Chain of Craters Road (from circa 1995).
Weathered aa lava flow, Kalapana Region, Big Island of Hawaii
1974 Aa lava flow, Chain of Craters Road, Hawaiian Volcanoes National Park.
Pyroclastic material from Kilauea volcano, Hawaii.
Olivine crystals (green) and Pele's Tears (black oval) in pyroclastic debris along Devastation Trail, Hawaii Volcanoes National Park. (In the palm of a hand.)
Between 100 and 2000 metric tons of sulfur dioxide (SO2) are released per day from Kilauea. The rain is so acidic that a desert has formed downwind from the summit of the volcano.
Sulfur Banks, Hawaii Volcanoes National Park. Sulfur and other minerals are being deposited here from gases rising from the hot magma below. The steam contains mostly water vapor, with lesser amounts of carbon dioxide and hydrogen sulfide.
Warning signs about gases in Hawaii Volcanoes National Park.
A nuee ardente from Mount Pelee, on the Caribbean island of
Martinique, destroyed the town of St. Pierre in 1902, killing almost all of its 28,000 inhabitants at once
(a prisoner in a dungeon, a shoemaker, and a few people on ships in the harbor survived).
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Volcano diagrams used with permission of Bruce E. Herbert, Texas A & M University, Big Bend Virtual Field Trip
This page created by
Pamela J. W. Gore
Georgia Perimeter College, Clarkston Campus, Clarkston, GA
Modified March 4, 1998
Modified July 17, 1999
Photo added Feb 3, 2006
Typo corrected Aug 22, 2007