Chapter 9 Volcanoes

Section 1 Volcanic Eruptions Volcano – a mountain that forms when molten rock, called magma, is forced to the Earth’s surface.

Nonexplosive Eruptions Lava – magma that flows onto Earth’s surface. Lava flows are associated with nonexplosive eruptions.

Explosive Eruptions Clouds of hot debris and gases shoot out from the volcano Volcano may actually decrease in size.

Cross Section of a Volcano Lava Vent Magma Chamber

Magma The composition of the magma determines the explosiveness of the volcano. Water content More water = more explosion Example: Soda Can Silica Content More silica = slow flowing magma (high viscosity) Discovery: Volcano

What erupts from a Volcano? Lava: Blocky Lava Pahoehoe Aa Pillow Lava

What erupts from a Volcano? Pyroclastic Material – the rock fragments created by a volcanic eruption. Volcanic Blocks Volcanic Bombs Lapilli Volcanic Ash

Section 2 Volcanoes’ Effects on Earth An Explosive Impact – Ashe – high into atmosphere – blocks sunlight Makes it hard to breathe Blocks roads

Flows and Fallout Lahar – a mixture of mud, groundwater, flowing at a rapid speed down the mountain after an eruption.

Pyroclastic Flows Rapidly flowing clouds of hot ash and volcanic glass rolling down the mountainside. Can cut down houses, trees, block roads, and devastate river valleys.

Climatic Changes Volcanic ash and sulfuric gases can reach the upper atmosphere. These gases can affect the amount of sunlight reaching the ground. Mount Pinatubo, 1991 Average global temperatures dropped as much as 0.5 degrees Celsius.

Three Types of Volcanoes Shield – built by repeated nonexplosive eruptions where lavaflows slowly build the mountain. Cinder Cone – small volcanoes made from pyroclastic materials of moderately explosive eruptions. Composite (Stratovolcanoes) – explosive eruptions followed by outpourings of lava. Layered Volcano

Craters and Calderas Crater – funnel shaped pit at top of the volcano Caldera – when a magma chamber empties and the roof collapses.

Lava Plateaus Large layers of lava flowing from fissures in the ground. Columbia River Plateau

Section 3 - What Causes Volcanoes? The Formation of Magma In the lower crust / upper mantle large reservoirs of magma form. Pressure / Temperature – affect magma formation Density – magma rises because it is less dense than the surrounding rock.

Ring of Fire Boundary around the Pacific Plate – 75% of the world’s active volcanoes.

Hot Spot Volcanoes An isolated volcano not caused by movement at a plate boundary, but rather by the melting of a mantle plume.