Lab #3 Volcanoes dantes peak 5

.docx

School

Wallace State Community College *

*We aren’t endorsed by this school

Course

111

Subject

Geology

Date

Apr 3, 2024

Type

docx

Pages

Uploaded by haleyeverett4

Rev 5.24.2023 1 PHS 111 Lab #3 Volcanoes & “Dante’s Peak” Name: Date: In answering any questions please do not just provide a yes or no response, explain your answer if it seems to be a yes or no questions. Volcanoes have fascinated and terrified humans from prehistoric times through the present. Volcanoes have inspired poets and religions, nourished societies and extinguished civilizations. Even today an eruption can be simultaneously beautiful and fearsome. An eruption is an overwhelming reminder of the tremendous forces still active within our Earth, forces over which humans have little if any control. Purpose: -This lesson will familiarize the student with volcanic processes and the factors that determine the eruptive style, products, and global distribution of the different types of volcanoes. The objectives are: 1. To learn the different types of volcanoes. 2. To understand the effect of magma composition on eruptive style and type of volcanic deposit. 3. To understand the tectonic environments of volcanism and the geographic distribution of volcanoes. 4. To learn about and identify potentially active volcanoes in the United States. Types of Volcanoes Volcanoes form where magma and its associated gases from deep within the earth break through the earth’s surface in the form of lava, pyroclastic debris, or a combination of the two. Over time, these deposits build an array of volcanic topographic features, which are classified primarily by their topographic form. Shield Volcanoes https://volcanoes.usgs.gov/vsc/glossary/lava_fountain.html A typical shield volcano eruption usually starts out with lava fountains , spurts of basaltic lava flung in the air as gas rapidly escapes. A string of lava fountains sometimes erupts from a fissure, producing a “curtain of fire.” Once most of the dissolved gasses are released, the eruption is usually characterized by a reduced outpouring

Rev 5.24.2023 2 of non-viscous or highly fluid basaltic lava. These lava flows may extrude from a central vent and/or fissures that open along the volcano’s flanks. The results are enormous and gently sloping (2 to 10 degrees) shield volcanoes, created by thousands of individual lava flows. The nature of basaltic lava allows it to flow for great distances as thin sheets, thus preventing it from supporting steep slopes. The Island of Hawaii consists of five huge shield volcanoes, two of which Kilauea (pictured on previous page; taken from https://volcanoes.usgs.gov/volcanoes/kilauea/ ), and Mauna Loa, are active much of the time. These Hawaiian volcanoes are the largest volcanoes on the planet. Mauna Loa is nearly 100 kilometers wide at the base and rises nearly 10 kilometers above the surrounding sea floor. Its volume is estimated to be about 50,000 cubic kilometers. By contrast, the largest volcano in the continental United States, Mount Shasta in northern California, has a volume of 205 cubic kilometers. Lava Plateaus Mafic magma, breaking through oceanic crust as a point source of basaltic lava creates Hawaiian-types shield volcanoes on the sea floor. However, when mafic magma breaks through continental crust along faults or fractures as a linear source of basaltic lava (also known as a fissure eruption), lava plateaus are created instead. These are related to shield volcanoes in that they are vast areas covered by basalt. The Columbia River Plateau in Washington and Oregon (image below), and the Snake River Plain in Idaho are examples. Lava plateaus are created when basaltic lava pours from long fissures for an extended period of time, ultimately burying the surrounding countryside. The Columbia River Plateau, for example, is more than one mile thick and contains individual flows that cover huge areas, in one case more than 40,000 square kilometers.

Rev 5.24.2023 3 Cinder Cones If the magma reaching the earth’s surface is highly charged with dissolved gasses, an explosive eruption of pyroclastic debris may result. Most of the pyroclastic debris explosively ejected during a volcanic eruption falls near the magma conduit. If a volcano has a prolonged eruptive history, layer upon layer of pyroclastic debris will accumulate to form a cinder cone, but such cones of pyroclastic debris rarely exceed 400 meters in height. A central crater , or saucer-shaped depression, is usually maintained during cone construction because of the continual expulsion of pyroclastic debris at the summit. Wizard Island in Crater Lake, Oregon, is an example of a cinder cone, as is the volcano Paricutin; which constructed its cone in the middle of a corn field in Mexico more than fifty years ago. Crater Lake Caldera with Wizard Island cinder cone and lava flows, some of the youngest features in the caldera as seen from Merriam Point. Viewed toward the south. Oregon. Taken from https://volcanoes.usgs.gov/volcanoes/crater_lake/crater_lake_geo_hist_138.html Cinder cones erode easily because they are constructed of unconsolidated pyroclastic debris. In contrast, rocks formed by the crystallization of magma within the volcanic conduits are resistant to erosion. They often remain as isolated and steep topographic pillars or volcanic necks after the cinder cones have been eroded away. Composite Volcanoes Some volcanoes are characterized by eruptive cycles that start out with the explosive ejection of pyroclastic debris and finish with less violent extrusion of lava flows. If this cycle is repeated often during the eruptive life of a volcano, the alternating pyroclastic layers and lava flows accumulate around the central vent to create a composite volcano (also known as a stratovolcano), which is often symmetrical. These volcanoes typically have concave upward profiles with slopes at their summits reaching as much as 30 degrees and slopes town their bases decreasing to fewer than 5 degrees.

Rev 5.24.2023 4 Composite volcanoes often erupt violently because the gases in the viscous magma build to very high pressure before the stiff magma finally breaks through the surface. Volcanic ash produced by large explosive eruptions may be carried around the world. The violent eruption of Mount Saint Helens in 1980 gave geologists an unprecedented opportunity to study the eruptive stages pf a typical composite volcano. Major eruptions of composite volcanoes are usually preceded by small bursts of steam or ash as small pockets of gas escape. Subsequently, the lava and overlying material violently explode into pyroclastic fragments of all sizes. The expelled debris is either thrown vertically into the air or cascades down the flanks of the volcano in clouds of red hot gas and pyroclastic debris. Mount Rainier , the highest peak in the Cascade Range at 4,392m (14,410 ft), forms a dramatic backdrop to the Puget Sound region. During an eruption 5,600 years ago the once-higher edifice collapsed to form a large crater open to the northeast much like that at Mount St. Helens after 1980. Ensuing eruptions rebuilt the summit, filling the large collapse crater. Large lahars (volcanic mudflows) from eruptions and from collapses of this massive, heavily glaciated andesitic volcano have reached as far as the Puget Sound lowlands. Since the last ice age, several dozen explosive eruptions spread tephra (ash, pumice) across parts of Washington. The last magmatic eruption was about 1,000 years ago. Extensive hydrothermal alteration of the upper portion of the volcano has contributed to its structural weakness promoting collapse. An active thermal system driven by magma deep under the volcano has melted out a labyrinth of steam caves beneath the summit icecap. https://volcanoes.usgs.gov/volcanoes/mount_rainier/ In some cases, the magma chamber feeding the volcano may be emptied in a single eruption. The unsupported roof at the summit might then collapse into the evacuated chamber, leaving a large, steep-walled depression called a caldera on the summit surface. Crater Lake in Oregon, pictured on page 3 under Cinder cones because of Wizard Island, is really a caldera that formed when Mount Mazama, an ancient composite volcano, blew its top about 6,600 years ago. Calderas may form at the summit of any volcano, but they form most often in composite volcanoes. A volcanic crater technically becomes a caldera when its diameter exceeds one kilometer. Composite volcanoes are the typical large textbook volcanoes of the continents and the island arcs. Familiar examples include Mount Fujiyama in Japan, Mount Vesuvius in Italy, and many of the volcanic peaks in the Cascade Range in the northwestern United States

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help