Volcanism and Extrusive Rocks Physical Geology 12/e, Chapter 4

Volcanism and Earth’s Systems Atmosphere originally created from gases released from volcanic eruption Hydrosphere produced by condensation of volcanic water vapor Biosphere both positively and negatively influenced by volcanism –Lava flows and ash weather to produce fertile soils –Violent eruptions can destroy nearly all life in their paths –Large amounts of ash and volcanic gases in atmosphere can trigger rapid climate changes and contribute to mass extinctions

Title + 10 Pages –Titles/heading –10 or fewer words per title –SHARE

Volcanic Eruptions Lava is produced when magma reaches Earth’s surface Explosive eruptions can produce rapidly cooled rock fragments called pyroclasts –Size range from dust (ash) to boulders (blocks and volcanic bombs) Calm oozing of magma out of the ground produces lava flows Pyroclastics and lava flows form extrusive igneous rocks Lava flows and pyroclasts pile up to form volcanoes

Eruptive Violence and Physical Characteristics of Lava Violence of eruptions controlled by: 1.Dissolved gases in the magma Water vapor, carbon dioxide, sulfur dioxide, etc. 2.Ease/difficulty of gases escaping to atmosphere Viscosity- a fluid’s resistance to flow 1.Silica content Higher silica contents produce higher viscosities 2.Lava temperature Cooler lavas have higher viscosities 3.Amount of dissolved gases The more dissolved gases, the more fluid the lava

Eruptive Violence and Physical Characteristics of Lava cont. page Igneous Family Silica Content ViscosityViolence of Eruption Silicic (Felsic)

Exit Ticket 1)Give an example of a real life substance that has high viscosity. 2)Give an example of a real life substance that has low viscosity.

Eruptive Violence and Physical Characteristics of Lava cont. page Igneous Family Silica Content Viscosity & Flow Violence of Eruption Silicic (Felsic) 65% (Silica Rich) High & Sluggish Violent Intermediate35-50%BothViolent and Lava Flows MaficLess than 50% Deficient Low & Easily Minimal More flows

Extrusive Rocks and Gases Scientific Investigation of Volcanism –Rocks, gases and events from observed eruptions compared to similar lavas elsewhere to infer the nature of past activity Rock Composition –Rhyolite - high silica; light color –Basalt - low silica; dark color –Andesite - intermediate silica and color

Extrusive Textures Texture - appearance of a rock with respect to size, shape and arrangement of its grains Glassy - glass without mineral crystals –Obsidian Fine-grained - most crystals < 1 mm –e.g., Basalt Porphyritic - larger crystals in a matrix of much finer crystals (groundmass) or glass –e.g., Andesite

Extrusive Textures Vesicular/Frothy - trapped gas bubbles –Vesicular basalt –Pumice Fragmental - particles blasted apart by explosive eruptions –Dust and ash (<2 mm) –Cinders (2-64 mm) –Blocks and bombs (>64 mm)

Volcanic Landforms Vent - opening through which lava erupts Crater - basin-like depression over the vent at the summit of the volcano Caldera - volcanic depression much larger than the original crater, having a diameter of at least 1 km

Types of Volcanoes pages TypeDiagramDefine & any charac. LifespanEruptive Material Rock Type Shield Composite (Stratovolcano) Cinder Dome

Virtual Volcano Build your own volcano –Write down the characteristics – lcano/index.cfm?title=Virtual%20Volcano

What am I???

Types of Volcanoes Shield volcanoes –Broad –Gently sloping –Composed of solidified lava flows –Flows often contain lava tubes Cinder cones –Small –Steeply sloping –Composed of a pile of loose cinders

Types of Volcanoes Composite volcanoes –AKA stratovolcanoes –Moderately to steeply sloping –Constructed of alternating layers of pyroclastic debris and solidified lava flows –Composed primarily of intermediate composition volcanic rocks (i.e., andesite) –Most common type of volcano at convergent plate boundaries (e.g., Pacific Ring of Fire) Volcanic domes –Extremely high viscosity, degassed, felsic lavas (often glassy, e.g., obsidian)

Other Eruption Types Flood eruptions –Very fluid (basalts) –Extremely large in volume –Create extensive lava plateaus –Eruption times correspond with largest mass extinction events Submarine eruptions –Nearly always basaltic –Mid-ocean ridge eruptions –Pillow basalts Columbia river flood basalts Pillow basalts

Volcanism on Other Planets Shield volcanoes –Venus, Mars, Io Lava domes –Venus, Moon Flood eruptions –Very fluid (basalts) –Extremely large in volume –Extensive flat lava plains (Moon, Mars, Venus, Mercury?) Insert Fig here Insert Fig A here Insert Fig A here Olympus Mons on Mars Lava domes on Venus Lava channel in volcanic plains on Moon Volcanic eruption on Io

End of Chapter 4