Transcript Volcanoes
VOLCANOES CHAPTER 12 HOW DO VOLCANOES AFFECT PEOPLE? WHAT CONDITIONS CAUSE VOLCANOES TO FORM? WHAT IS THE RELATIONSHIP BETWEEN VOLCANOES AND PLATES? SECTION 1: VOLCANOES AND EARTH’S MOVING PLATES MOST ACTIVE VOLCANOES • Hawaii • Kilauea (kee low AY ah) is the world’s most active volcano • May 1990 eruption destroyed the town of Kalapana Gardens • Eruptions on and off since January 1983 • Iceland • Hekla eruption February 2000 • Iceland sits on an area where Earth’s plates more apart • Known as the island of fire and ice EFFECTS OF ERUPTIONS HUMAN ENVIRONMENTAL Evacuations occur with enough warning – people must leave their homes. Sulfurous gases from an eruption mix with water vapor to form acid rain. At times, everyone in the path is completely destroyed, homes, cars; towns are buried in ash. Vegetation, lakes and streams are devastated by acid rain. HOW DO VOLCANOES FORM? • Deep inside Earth, heat and pressure changes cause rock to melt • This magma is slowly forced upward toward the Earth’s surface • After many, many years of this process, magma reaches the surface and flows out through an opening called a vent • As the lava flows out and cools, it forms igneous rock around the vent. The steep walled depression around the volcano’s vent is the crater. WHERE DO VOLCANOES OCCUR? DIVERGENT BOUNDARIES • Plates moving apart • Iceland is part of the Mid-Atlantic Ridge and located in the Artic Circle • Plate separate forming rifts • Lava flows from the rifts and as it cools, builds layers of rock • Sometimes, the eruptions rise above sea level, forming new islands (like Iceland) • Island of Surtsey was formed in 1963 CONVERGENT BOUNDARIES • Plates move together • Oceanic plates slide underneath continental plates • Andes Mountains in South America • Volcanoes at convergent boundaries tend to erupt more violently than others • Island of Monteserrat Volcano • • July 1995 Destroyed towns, vegetation and killed people HOT SPOTS • Hot rock at areas between Earth’s mantle and core is forced toward the crust where it melts partially (this is NOT a plate boundary) • Hawaiian Islands (p. 333 Figure 5) • Formed from volcanic activity over a period of 5 million years • Five of the islands are volcanoes • Hot spot is stationary while the pacific plate moves (causing the islands to actually change locations) HANAUMA BAY, HAWAII Formed through a series of violent volcanic eruptions, it is now a flooded crater. HANAUMA BAY, HAWAII A nature preserve popular among tourists for the beautiful coral reefs and wildlife FOR TOMORROW • Define “tephra” in your notes • Read Section 2 pg. 336 – 343 • Bring a few colored pencils to diagram volcanoes! HOW IS THE EXPLOSIVENESS OF A VOLCANIC ERUPTION RELATED TO THE SILICA AND WATER VAPOR CONTENT OF ITS MAGMA? WHAT ARE THE THREE TYPES OF VOLCANOES? SECTION 2 TYPES OF VOLCANOES ERUPTIONS When you think about a volcanic eruption, what do you see in your head? • Two major factors influence how an volcano erupts: • Water Vapor & Trapped Gases Present in the Magma • Silica content in the magma ERUPTIONS TRAPPED GASES WATER VAPOR Example: What happens when you shake a can of coke and then open it? At convergent plate boundaries, oceanic plates are involved. Gases can escape quietly or explode all at once, like a shaken Coke. The more water vapor present in the magma, the more explosive the eruption. SILICA POOR MAGMA QUIET ERUPTIONS • Basaltic Magma • Fluid & quiet; lava pours from the vents and runs down the sides of the volcano • Types of lava (pg. 338) • Pahoehoe- rope like, smooth • Aa- chunks of rocdk, shapr • Pillow- pillow shape chunks, most common type. SILICA RICH MAGMA EXPLOSIVE ERUPTIONS • When plates slide underneath each other and the rock melts, the magma is forced upward • Thick magma with lots of trapped gases • Andesitic magma • Granitic magma TYPES OF VOLCANOES SHIELD VOLCANO • Broad volcano with sloping sides • Example – Hawaiian Islands • Basaltic Lava • What type of eruption? • Can flow onto Earth’s surface through cracks called fissures • Creates flood basalts, which is where most of the material inside the volcano comes out at SHIELD VOLCANO CINDER CONE VOLCANO • Steep sided, loosely packed • Forms from tephra falling to the group from explosive volcanic eruptions • Paricutin • February 1943 • Farmed noticed a large hole in his cornfield suddenly had hot, glowing cinders in it. Over the next few days, cinders were thrown into the air from the opening, creating a cinder cone volcano CINDER CONE VOLCANO COMPOSITE VOLCANO • Some volcanoes alternate between quiet and explosive eruptions • Formed from a cycle of explosive and quiet eruptions, causing lava and tephra to layer on top of each other • Found mostly where Earth’s plates come together • Example – Mount Rainer in Washington COMPOSITE VOLCANO THREE TYPES OF VOLCANOES UPCOMING Section 1 & 2 Review Worksheet Bill Nye “Volcanoes” PROJECT RESEARCH DAY FRIDAY. You need to have chosen your volcano by Friday. Section 3 –Monday Test – Wednesday PROJECTS DUE THURSDAY, 1/16 AND FRIDAY, 1/17. WHAT ARE IGNEOUS ROCK FEATURES AND HOW DO THEY FORM? HOW DOES A VOLCANIC NECK AND A CALDERA FORM? SECTION 3 IGNEOUS ROCK FEATURES