Volcanic Eruptions 3.3 Objectives: Explain what happens when a volcano erupts. Describe 2 types of volcanic eruptions Identify stages of volcanic activity

Volcanic Eruptions 3.3 What comes out of volcanic explosions? Ash, lava, steam, rock, gases, dirt Magma forms in the asthenosphere Convection currents in the mantle bring magma towards the surface Magma tries to flow into any open crack When magma reaches a weak spot in the crust, a volcano forms Lava is magma that has reached the surface

Magma Reaches Earth’s Surface Volcanoes are systems of passage ways through which magma moves. Inside a Volcano Magma collects below the volcano in the magma chamber Magma flows upward through a tube (pipe) that connects the magma chamber to the surface.

Magma Reaches Earth’s Surface Inside a Volcano Gas and magma leave through vents Central vent is the opening at the top Side vent anywhere along the side of the volcano Lava pours out of the vents and creates a lava flow A bowl shaped area called a crater may form around the central vent

Crater Vent Pipe Side Vent Lava Flow Magma Chamber

Magma Reaches Earth’s Surface A Volcanic Eruption Dissolved gases are trapped in magma under extreme pressure (CO2 in a soda bottle) as magma flows , pressure because there is less rock on top of it. the dissolved gases expand and form bubbles When a volcano erupts, the force of the expanding gas forces magma up the pipe until it explodes out the vent

Content checkpoint… think/pair share…take two minutes to answer these questions with a partner nearby….. What common everyday occurrence can we relate to a volcanic eruption? What happens to the pressure in the magma as it rises toward the surface?

Kinds of Volcanic Eruptions Volcanic eruptions can be quiet or explosive. Eruptions depend on the properties of magma Silica content Viscosity

Kinds of Volcanic Eruptions Quiet Eruptions Magma has low silica content = low viscosity Magma flows easier so gases bubble out gently Lava can flow many kilometers from the vent Produce both pahoehoe and aa lava Example: Hawaiian Islands – Mount Kilauea

Kinds of Volcanic Eruptions Explosive Eruptions Magma has high silica content = high viscosity Magma doesn’t always flow out of vent and so it builds up (like a cork in a bottle) Trapped gases build up pressure until they explode Magma is pushed out of the vent with incredible force

Kinds of Volcanic Eruptions Explosive Eruptions Lava breaks into fragments that cool quickly and harden into different sizes Ash – fine, dust sized particles of lava Cinders – pebble sized particles Bombs – baseball to car sized chunks of lava Pyroclastic flow: when an explosive eruption hurls out gases, ash, cinders and bombs. Pumice forms when lava cools quick and traps air bubbles inside Obsidian forms when lava cools quick leaving the surface smooth and glass-like

Kinds of Volcanic Eruptions Volcano Hazards Quiet eruptions cause lava to flow far --- burning and burying everything in its path Explosive eruptions can bury entire towns in ash, cause landslides, avalanches, cause damage from gases and cinders/bombs.

Content checkpoint… think-pair-share take two minutes to answer these questions with a partner nearby. What is pyroclastic flow? How does volcanic ash cause damage? What is the main difference between a quiet eruption and an explosive eruption?

Stages of Volcanic Activity Life Cycle of a Volcano Scientists use historical records and monitor volcanoes to determine what stage of activity a volcano is in A volcano can be active, dormant or extinct An active volcano is erupting or showing signs of near future eruptions A dormant (sleeping) volcano can awaken in the future and become active An extinct (dead) volcano is unlikely to erupt ever again

Stages of Volcanic Activity Monitoring Volcanoes Geologists use tiltmeters to detect slight changes in surface elevation cause by magma moving underground They monitor gases escaping from a volcano Increase in temperature might mean magma is nearing the surface The changes detected may give a short warning time BUT We cannot be certain the type of eruption or how powerful it will be

Think and Discuss…. Which is more likely to be dangerous – a volcano that erupts frequently or a volcano that has been inactive for a hundred years? WHY?