10 1 The Nature of Volcanic Eruptions Factors

10. 1 The Nature of Volcanic Eruptions Factors that determine the violence of an eruption. • 1 - Composition of the magma • 2 - Temperature of the magma • 3 - Dissolved gases in the magma

10. 1 The Nature of Volcanic Eruptions Factors Affecting Eruptions Viscosity- is the measure of a material's resistance to flow. • Factors affecting viscosity 1. Temperature 2. Composition A. High silica—high viscosity B. Low silica—more fluid

10. 1 The Nature of Volcanic Eruptions Factors Affecting Eruptions u Dissolved gases • Mainly water vapor and carbon dioxide • Provide the force to extrude lava - More Viscous magma produces a more violent eruption.

10. 1 The Nature of Volcanic Eruptions Volcanic Material u Lava Flows • Types of lava - Pahoehoe lava (resembles braids in ropes)

Pahoehoe (Ropy) Lava Flow

Slow-Moving Aa Flow - Aa lava (rough, jagged blocks)

Slow-Moving Aa Flow

10. 1 The Nature of Volcanic Eruptions Volcanic Material u Pyroclastic Materials particles produced in volcanic eruptions.

10. 1 The Nature of Volcanic Eruptions Volcanic Material • Types of pyroclastic material - Ash and dust—fine, glassy fragments - Pumice—, air-filled lava

10. 1 The Nature of Volcanic Eruptions Volcanic Material - Volcanic Bombs

10. 1 The Nature of Volcanic Eruptions Anatomy of Volcanoes • crater is the depression at the summit. • conduit, or pipe, carries gas-rich magma to the surface.

Anatomy of a “Typical” Volcano

10. 1 The Nature of Volcanic Eruptions Types of Volcanoes u 1 - Shield Volcanoes-are broad, gently sloping volcanoes built from fluid basaltic lavas.

Shield Volcanoes

Shield Volcanoes

Cinder Cones u 2 -Cinder Cones-small volcanoes built primarily of pyroclastic material ejected from a single vent. - Small in size, Steep slope angle, and often appear in groups

Cinder Cones

10. 1 The Nature of Volcanic Eruptions Types of Volcanoes u 3 -Composite Cones/ Strato • composed of both lava flows and pyroclastic material. - Large size, Most violent type of activity - Most are adjacent to the Pacific Ocean (e. g. , Mt. Shasta).

Composite/ Strato Cones Mt. Rainer

Composite/ Strato Cones

Mount St. Helens Before and After the May 18, 1980, Eruption

Profiles of Volcanic Landforms

10. 1 The Nature of Volcanic Eruptions Other Volcanic Landforms u Calderas- are large depressions in volcanoes

10. 1 The Nature of Volcanic Eruptions Other Volcanic Landforms u Lava Plateaus • Fluid basaltic lava extruded from crustal fractures called fissures.