Learning Objectives - I can distinguish between nonexplosive & explosive volcanic eruptions. I can distinguish between nonexplosive & explosive volcanic eruptions. I can identify the features of a volcano. I can identify the features of a volcano. I can explain how the composition of magma affects the type of volcanic eruption that will occur. I can explain how the composition of magma affects the type of volcanic eruption that will occur. I can describe the four types of lava & four types of pyroclastic material. I can describe the four types of lava & four types of pyroclastic material.

Ch.6, Sec.1 - Volcanic Eruptions  volcano: a vent or fissure in the Earth’s surface through which magma and gases are expelled - - molten rock in volcanoes is called magma & lava is molten rock on Earth’s surface Nonexplosive Eruptions Nonexplosive Eruptions - these eruptions are the most common type and they produce calm flows of lava Explosive Eruptions Explosive Eruptions - these eruptions are less common and blow dust-size ash particles into the atmosphere with millions of tons of lava

Ch.6, Sec.1 - Volcanic Eruptions Mount St. Helens before the eruption of May 18, 1980 Mount St. Helens 30 years after the eruption in May, 2010

Ch.6, Sec.1 - Volcanic Eruptions What Is Inside a Volcano? What Is Inside a Volcano?  magma chamber: the body of molten rock that feeds a volcano  vent: an opening at the surface of the Earth through which volcanic material passes Popocatepetl, Mexico (17,802ft.)

Ch.6, Sec.1 - Volcanic Eruptions What Makes Up Magma? What Makes Up Magma? - the key to whether an eruption will be explosive lies in the silica, water, and gas content of the magma - if the water content is high, an explosive eruption is likely to occur due to high pressure in the rock, once it rises to the surface and turns gaseous (think about shaking a can of soda) - if the silica content is high, an explosive eruption is likely to occur due to high pressure in the vents caused by built-up, hardened magma

Ch.6, Sec.1 - Volcanic Eruptions

What Erupts from a Volcano? What Erupts from a Volcano? - explosive eruptions produce pyroclastic material (ash, blocks of rock, bombs of rock) - nonexplosive eruptions produce liquid magma called lava (Pillow, Blocky, Aa, Pahoehoe) 1. Pillow Lava – forms when lava erupts underwater (low viscosity, so flows quickly) Lava Lava

Ch.6, Sec.1 - Volcanic Eruptions 2. Aa Lava – pours out quickly & forms a brittle crust (low viscosity, so flows quickly) 3. Blocky Lava – usually oozes out slowly & forms sharp- edged chunks (high viscosity, so flows slowly) 4. Pahoehoe Lava – flows very slowly with a glassy surface (high viscosity, so flows slowly)

Ch.6, Sec.1 - Volcanic Eruptions

Pyroclastic Material Pyroclastic Material 1. Ash – forms when the gases in stiff magma expand rapidly and the walls of the gas bubbles explode into tiny particles 2. Lapilli – forms from magma that has hardened before hitting the ground (also called cinders)

Ch.6, Sec.1 - Volcanic Eruptions 3. Volcanic Bomb – large blobs of magma that harden & spin in the air before landing 4. Volcanic Block – the largest pieces of pyroclastic material are made from solid rock

Ch.6, Sec.1 - Volcanic Eruptions Mount St. Helens, Washington Pumice Plain Crater

Ch.6, Sec.1 - Volcanic Eruptions Pyroclastic Flows Pyroclastic Flows - produced when enormous amounts of ash, dust, and gases are ejected from a volcano - these flow at speeds of up to 125mph with temperatures reaching 1300°F! - these flows can create lahars, which are massive water- saturated mudflows, which have the consistency of wet cement