Lab 5b: Volcanic Hazards

 

Objectives:

-          Review where magma forms

-          Types of volcanoes and how they form

-          Identifying hazards: type and extent

-          Set up for next weeks lab, looking at igneous rocks

 

Introduction:

            Magma formation:

                        Hot spots – middle of plates

                        Divergent Boundaries – extension, decomp. melting, formation of new crust

                        Convergent Boundaries – subduction, flux melting, formation of volcanic range

 

Volcanoes:

            Types of volcanoes:

                        Shield: Low broad volcano, covering a large area and not very high

                                    Form from effusion of magma, spreads out over area

                                    100’s m to a few km thick, 100’s-1000’s km²

                                                Layers of lava flows from fractures and fissures

                                    Little ash or pyroclastic material

                                    Hot spots - Hawaii

                        Composite/Stratovolcano: steeper taller volcano

                                    From build up of layers of lava and pyroclastics

                                    Less than 100 km across

                                    Lots of pyroclastics, violent eruptions

                                    Convergence - Cascades

                        Cinder Cones: small isolated cones

                                    Loose pyroclastic debris

                                    <10 km across

 

Hazards (volcanic type and distribution):

            Tephra fallout: Pyroclastic materials that fly from an erupting volcano through the air

before cooling, and range in size from fine dust to massive blocks

            Pyroclastic density currents: A rapid, extremely hot, downward stream of particles and

chunks of igneous rock ejected from a volcanic vent during an eruption, air, gases, and ash ejected from an erupting volcano. Can be 800ºC or more and may move at speeds exceeding 150 kilometers per hour.

            Lahar: A flow of pyroclastic material mixed with water. Often produced when a snow-

capped volcano erupts and hot pyroclastics melt a large amount of snow or ice

            Rock avalanches: from seismicity

            Lava flows: Magma that comes to the Earth's surface through a volcano or fissure