Review Volcanoes

Question 1 Lava with a high viscosity is runny, almost like water. smells like sulphur. is thick, like pudding. dries smooth and glassy. The viscosity of magma and lava depends on both temperature and composition. The hotter the magma or lava, the lower the viscosity. Magmas and lavas high in silica have higher viscosities than magmas and lavas low in silica. Something that is fluid or quickly pours it has little viscosity. Cold syrup pours very slowly and has a high viscosity.

Question 2 A shield volcano is sometimes called a stratovolcano. has gently sloping sides. has a jagged surface. forms when lava erupts underwater. A shield volcano is a mountain with broad, gently sloping sides and a nearly circular base that forms when layer upon layer of basaltic lava accumulates during nonexplosive eruptions.

Question 3 A combination of explosive and nonexplosive eruptions will create a shield volcano. cinder cone volcano. composite volcano. plateau volcano. Composite volcanoes are large volcanoes that form when layers of volcanic fragments alternate with lava. The magma that forms composite volcanoes commonly contains large amounts of silica, water, and gases, making these volcanoes violently explosive. Also called stratovolcano, a term for steep-sided, often symmetrical cones constructed of alternating layers of lava flows, ash, and other volcanic debris. Composite volcanoes tend to erupt explosively and pose considerable danger to nearby life and property.

Question 4 Where are volcanoes most likely to form? near the center of continents along plate boundaries along bodies of water in mountainous areas Most volcanoes form at plate boundaries. About 80 percent of all volcanoes are found along convergent boundaries. About 15 percent are found along divergent boundaries. Only about 5 percent of extrusive igneous activity occurs far from plate boundaries.

Question 5 Pyroclastic material forms when lava flows calmly from a crack in the Earth’s crust. magma remains underground too long. magma explodes into the air and hardens. lava flows underwater. Tephra are rock fragments thrown into the air during a volcanic eruption. A pyroclastic flow is a cloud of volcanic gas, dust, and other tephra traveling at speeds of nearly 200 km/h. The temperature at the center of a pyroclastic flow can exceed 700°C.

Question 6 The depression created when the roof of a magma chamber collapses is called Caldera. lava plateau. Crater. lapilli. A crater is a bowl-shaped depression at the top of a volcano that is connected to the magma chamber by a vent. Volcanic craters are usually less than 1 km in diameter. Calderas are large depressions up to 50 km in diameter that can form when the summit or the side of a volcano collapses into the magma chamber that once fueled the volcano.

Question 7 Rock begins to melt when both pressure and temperature decrease. both pressure and temperature increase. temperature increases and pressure decreases. temperature decreases and pressure increases. Magma forms when temperatures are high enough to melt the rocks involved, usually between 800°C and 1200°C. Pressure, which increases with depth, is one factor that determines whether rocks will melt to form magma. As pressure increases, the temperature at which a substance melts also increases. Due to the effects of pressure, most of the rocks in Earth’s lower crust and upper mantle do not melt to form magma.

Question 8 Some volcanoes are located far from plate boundaries and form as the result of hot spots. Hot spots are unusually hot regions of Earth’s mantle where high-temperature plumes of mantle material rise toward the surface. A plume does not move laterally, which results in a trail of progressively older volcanoes that formed as a plate moved over a hot spot. The Hawaiian Islands continue to rise above the ocean floor as the Pacific Plate moves slowly over a hot spot. The volcanoes of Hawaii and other places far from tectonic plate boundaries are known as Calderas. hot spots. mid-ocean ridges. viscous volcanoes.

Question 9 Highly explosive volcanoes tend to have what type of magma? magma with high silica, high viscosity, and higher gas content magma with low silica, low viscosity, and lower gas content magma with low silica, high viscosity, and lower gas content magma with no silica, high viscosity, and no gas content

Question 10 What type of volcano is built almost entirely from ejected lava fragments? cinder cone shield volcano composite cone pahoehoe volcano A cinder-cone volcano is a generally small, steep-sided volcano that forms when material ejected high into the air falls back to Earth and piles up around the vent. The magma that fuels these volcanoes contains more water and silica than shield volcanoes, which makes them more explosive in nature.

Question 11 The most violent volcanic eruptions are associated with what type of volcano? cinder cones composite cones shield volcanoes fissure eruptions Composite volcanoes are large volcanoes that form when layers of volcanic fragments alternate with lava. The magma that forms composite volcanoes commonly contains large amounts of silica, water, and gases, making these volcanoes violently explosive.

Question 12 The broad, slightly dome-shaped volcanoes of Hawaii are ____. composite cone volcanoes pyroclastic volcanoes shield volcanoes cinder cone volcanoes Shield volcanoes are by far the largest, and cinder-cone volcanoes are the smallest. Cinder-cone volcanoes have the steepest slopes, while shield volcanoes have the gentlest slopes. The slopes of cinder-cone and composite volcanoes are concave, and the slopes of shield volcanoes are straight.

Question 13 Volcanic activity is common along the Mid-Atlantic Ridge. This activity occurs at a mantle plume. divergent boundary. subducted plane. break in the continental crust. Divergent boundaries occur along spreading centers where plates are moving apart and new crust is created by magma pushing up from the mantle. Picture two giant conveyor belts, facing each other but slowly moving in opposite directions as they transport newly formed oceanic crust away from the ridge crest. Perhaps the best known of the divergent boundaries is the Mid-Atlantic Ridge. This submerged mountain range process has been going on for millions of years, it has resulted in plate movement of thousands of kilometers. Seafloor spreading over the past 100 to 200 million years has caused the Atlantic Ocean to grow from a tiny inlet of water between the continents of Europe, Africa, and the Americas into the vast ocean that exists today. The consequences of plate movement are easy to see around Krafla Volcano, in the northeastern part of Iceland. Here, existing ground cracks have widened and new ones appear every few months. Some of these rifting events were accompanied by volcanic activity; the ground would gradually rise 1-2 m before abruptly dropping, signalling an impending eruption.

Question 14 The hotter the magma or lava, the lower the viscosity. Which list places the magma types in order of decreasing viscosity (most viscous listed first)? basaltic, andesitic, rhyolitic andesitic, basaltic, rhyolitic rhyolitic, andesitic, basaltic basaltic, rhyolitic, andesitic Viscosity is the internal resistance to flow; the higher the viscosity, the thicker the magma. The viscosity of magma and lava depends on both temperature and composition. The hotter the magma or lava, the lower the viscosity. Magmas and lavas high in silica have higher viscosities than magmas and lavas low in silica.

Question 15 &16 What feature is labeled D in Figure 10-1? Pipe Crater volcanic neck lava flow What feature is labeled A in Figure 10-1? A vent or pipe is where lava erupts through an opening in the crust. As lava flows out onto the surface, it cools and solidifies around the vent, eventually accumulating to form a mountain known as a volcano. A crater is a bowl-shaped depression at the top of a volcano that is connected to the magma chamber by a vent.

Question 16 What type of volcano is illustrated in Figure 10-1? Bands indicate explosive eruptions that are then covered by layers of heavy flows of lava What type of volcano is illustrated in Figure 10-1? volcanic neck cinder cone shield volcano composite cone Composite volcanoes are large volcanoes that form when layers of volcanic fragments alternate with lava. The magma that forms composite volcanoes commonly contains large amounts of silica, water, and gases, making these volcanoes violently explosive.

Question 18 Which of the following plays a major part in determining the form of a volcano? elevation above sea level magma composition local soil type nearness of other volcanoes The appearance of a volcano depends on two factors: The type of material that forms the volcano The type of eruptions that occur Based on these two criteria, three major types of volcanoes have been identified: Shield volcanoes Cinder-cone volcanoes Composite volcanoes