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

10.1 The Nature of Volcanic Eruptions Factors Affecting Eruptions 10.1 The Nature of Volcanic Eruptions 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 10.1 The Nature of Volcanic Eruptions 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 10.1 The Nature of Volcanic Eruptions Pyroclastic Materials particles produced in volcanic eruptions.

10.1 The Nature of Volcanic Eruptions Volcanic Material 10.1 The Nature of Volcanic Eruptions • Types of pyroclastic material - Ash and dust—fine, glassy fragments - Pumice—, air-filled lava

10.1 The Nature of Volcanic Eruptions Volcanic Material 10.1 The Nature of Volcanic Eruptions - Volcanic Bombs

10.1 The Nature of Volcanic Eruptions Anatomy of Volcanoes 10.1 The Nature of Volcanic Eruptions • 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 10.1 The Nature of Volcanic Eruptions 1- Shield Volcanoes-are broad, gently sloping volcanoes built from fluid basaltic lavas.

Shield Volcanoes

Shield Volcanoes

Cinder Cones 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 10.1 The Nature of Volcanic Eruptions 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

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 10.1 The Nature of Volcanic Eruptions Calderas- are large depressions in volcanoes

10.1 The Nature of Volcanic Eruptions Other Volcanic Landforms 10.1 The Nature of Volcanic Eruptions Lava Plateaus • Fluid basaltic lava extruded from crustal fractures called fissures.