dynamic earth class 13 21 february 2006. volcanic imagination (chapter 4, continued) exploring the...
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![Page 1: Dynamic Earth Class 13 21 February 2006. Volcanic Imagination (Chapter 4, continued) Exploring the Earth ’ s Interior](https://reader036.vdocuments.mx/reader036/viewer/2022062806/56649d495503460f94a25dba/html5/thumbnails/1.jpg)
Dynamic Earth
Class 13
21 February 2006
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Volcanic Imagination(Chapter 4, continued)
Exploring the Earth’s Interior
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How do we know about the Earth’s Interior?
• Meteorites
• Direct observation
• High-pressure experimental petrology
• Earthquake waves (seismology)
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Layers of the Earth
• Crust
• Rigid upper mantle (+crust = lithosphere)
• Asthenosphere
• Upper mantle
• Lower mantle
• Outer core
• Inner core
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Earth’s internal heat•Original heat
•Subsequent radioactive decay
•Conduction
•Convection
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Crust as an Elastic Sheet
Continental ice loads the mantle
Ice causes isostatic subsidence
Melting of ice causes isostatic uplift
Return to isostatic equilibrium
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The less dense crust “floats” on the less buoyant, denser mantle
MohorovicicDiscontinuity
(Moho)
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Convection in Earth’s Mantle
• Convection happens when – Temperature gradient exists
– Heat is directional
– Conduction operates slowly
– Surface area to depth ratio is low
– Viscosity of material not extremely high
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Convection in Earth’s Mantle
• Assumptions– Solid mantle behaves fluidly over time
– Mantle and core do not mix
– Heat generated from within the Earth
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Temperature vs. Depth
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Convection as a Possible Mechanism for Plate Tectonics
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Mantle Tomography
• Uses numerous seismic data
• Uses small changes in speed of seismic waves
• Faster wave motion may correspond to denser or colder regions
• Slower wave motion may correspond to buoyant or warmer regions
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Basics of Tomography
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Tomography of the Mantle
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At 2770 km
Tomography at the Base of the Mantle
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Tomography Beneath Active Volcanoes
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Tomography Beneath Active Volcanoes
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Volcanic Activity on Earth
• Spreading centers (ridges)
• Island arc
• Hotspots
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Hotspots
• Areas with volcanic activity NOT explained by plate tectonics
• Mantle beneath may be hot, wet, or chemically different
• Commonly active for long time
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Global Hotspots
http://www.hvo.usgs.gov
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Flood basalts
Hotspot tracks
Oceanic plateaus
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Karoo / Etendeka Flood Basalts
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Columbia River Flood Basalts
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Linear Volcanic Chains
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Hawaiian Islands - Emperor Seamounts
QuickTime™ and aTIFF (LZW) decompressor
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The trail of the Hawaiian Hot Spot goes all the way to the far northwest Pacific
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In addition to the Hawaiian Hot Spot track, there are several others in the Pacific
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Age Progressions Along Volcano Chains
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Hawaiian Islands
Oldest
Youngest
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Hotspot Observations
• Volcanic activity, NOT explained by plate tectonics
• Active for long time
• Age varies (youngest in opposite direction of plate motion)
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Hot spots are regions in the Asthenosphere that are hotterthan their surroundings
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Molten magma rises to the surface to form volcanoes, similar to what happens at
Spreading Centers
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Hot spot volcanoes are relatively small, isolated
features.
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Hot spots are believed to be fixedrelative to the mantle.
BUT – this is controversial!
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When a plate moves over afixed Hot Spot,
a linear chain of volcanoes is formed.
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Oceanic crust
Lithosphericmantle
6-9 km
10-60 km
H o t
C o ld
200-400 km
Oceanic flood basalts
Hotspot Origins - Mantle Plumes
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Mantle plumes and eruption sizes
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Convection in the Mantle
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Convection and Mantle Plumes
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Why Linear Chains of Volcanoes?
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Model of Mantle Plumes
A mantle plume rising beneath a slow-moving plate or continent will “puddle” beneath the lithosphere
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Model of Mantle Plumes
When eruptions begin, they are voluminous, causing oceanic plateaus
and flood basalt provinces
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Model of Mantle Plumes
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Model of Mantle Plume
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Mantle Plume Shape Unknown
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Model of Mantle Plumes
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Models of Mantle Plumes
Wolfe et al., Nature, [1997]
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At 2770 km
Tomography at the Base of the Tomography at the Base of the MantleMantle
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Instability Causes Mantle Plumes
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How Can Plate Tectonics and Mantle Plumes Work Together?
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Why Are Hotspots Important
• Associated with Large Volcanic Eruptions– May inject gas and particles into air– May re-landscape large areas– May decrease habitable areas– May make life difficult for some plants and
animals (and cause mass extinction)
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Volcanic Eruptions and the Atmosphere
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Life on Earth is Difficult!
• Earthquakes
• Floods
• Climate changes (draught, ice ages)
• Other weather hazards (tornadoes, cyclones)
• Volcanic eruptions
• Meteor / asteroid impacts
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Meteor / Asteroid Impacts
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Meteor / Asteroid Impacts
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Environmental Catastrophes and Hotspots
End Cretaceous (65 Ma)
Eruption of Deccan Traps (Reunion hotspot)
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Extinction Percentages and Hotspots
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Extinction is Forever
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Dinosaurs - ~65 Ma
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Giant Ground Sloth ~10 Ka
Trilobites~ 300 Ma
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ThursdayVideo:
Death of the Dinosaurs