Geology Notes Part 9 1

What is a volcano? A vent or fissure in the Earth’s surface through which magma and gases are expelled 2

What is the difference between lava and magma? lava is the molten rock or magma that has reached the surface Lava Magma 3

Where do volcanoes generally occur? They generally occur along plate boundaries when plates collide or move apart 4

What are the two different types of volcanic eruption? nonexplosive or quiet eruptions produce calm flows of lava explosive eruptions are rare and rapidly erupt ash and rock into the atmosphere 5

What are the different types of lava? Aa lava is thin and forms brittle jagged crust as it cools Pahoehoe lava flows slowly forms a glassy wrinkled crust 6

What are the different types of lava? Pahoehoe Pahoehoe Aa Aa Aa 7

Pyroclastic Materials 8

What is a shield volcano and how do they form? formed by quiet eruptions thin lava that spreads out over a wide area sides are not steep 9

Photograph of the Hawaiian volcano, Mauna Kea, with a light dusting of snow, seen from Kohala above Kamuela. Photograph by Eric Guinther provided to Wikipedia under GNU. 10

Belknap Shield Volcano, Oregon. 11

What is a cinder cone volcano and how do they form? Formed by moderatly explosive eruptions the pyroclastic material forms steep sides 12

Tavurvur, Rabaul Caldera, Papua New Guinea Tavurvur, Rabaul Caldera, Papua New Guinea. A small explosion from Tavurvur sends an eruption column into the sky a few weeks after it began erupting on September 19, 1994. Lava erupted from the cone in October 1996 and flowed through the breach in the crater (left center). 13

Mount Veniaminof, Alaska Mount Veniaminof, Alaska. Steam rises from the cinder cone within the caldera of Mount Veniaminof in the final stages of an eruption in 1983-1984. Lava flows that spilled down the side of the cone (dark areas) melted a pit in the summit ice cap about 2.3 x 1 km in dimension. 14

What is a composite volcano and how do they form? Form from explosive eruptions followed by slower flow of lava forms alternating layers of pyroclastic material and lava Also known as a stratovolcano 15

Mount St Helens 1980 16

Snow-covered Kanaga Volcano in Alaska erupts a small column of tephra, gas, and steam. Kanaga is a stratovolcano. 17

What is a hot spot? A volcanically active area far from a plate boundary 18

How can hot spots be used to determine the motion of tectonic plate? Using the distance of volcanoes (such as the Hawaiian Islands) and their age, the direction and rate of plate movement can be determined. Distance ÷ Time 19

Current Eruption Thursday, January 13, 2011 - Mount Etna, Italy 20

How can volcanoes change the atmosphere, hydrosphere, and other Earth systems. The lava, gas, and ash that erupt into the atmosphere can remain in the atmosphere and be dispersed around the world by global wind currents. The sulfur dioxide combines with water vapor to form sulfuric acid, which reflects the sun’s energy back into space. This can cause global temperatures to decrease. Also the acid rain has a negative impact on vegatation around the world 21

How can volcanoes be used to determine plate boundaries? Composite volcanoes usually form in straight lines along convergent plate boundaries as one plate is being subducted under another. Convergent Boundaries 22