Download Types of Lavas Types of Basalts

Frank Press • Raymond Siever • John Grotzinger • Thomas H. Jordan
Understanding Earth
Fourth Edition
Chapter 6:
Volcanism
Lecture Slides prepared by
Bill Dupré • Peter Copeland
Copyright © 2004 by W. H. Freeman & Company
4. …accumulating on
the surface to form a
volcano.
3. Lavas erupt from
the magma chamber
through central and
side vents…
2. …rises through the
lithosphere to form a
magma chamber
Fig. 6.1
1. Magma, which
originates in the
partially melted
asthenosphere…
Types of Lavas
• Basaltic lavas: low-viscosity mafic lavas,
typically erupted at 1000o to 1200o C; cool to
form basalt.
• Rhyolitic lavas: high-viscosity felsic lavas,
typically erupted at 800o to 1200o C; cool to
form rhyolite.
• Andesitic lavas: intermediate in composition
and viscosity between mafic and felsic
magmas; cool to form andesite.
Flood Basalts of the Columbia Plateau
Types of Basalts
• Flood Basalts: thick, widespread accumulations
of basalt, typically fed by fissures
• Pahoehoe: a very low viscosity basaltic lava
characterized by a ropy texture
• Aa: a relatively low viscosity basaltic lava
characterized by a jagged, blocky texture
• Pillow Basalts: a basaltic lava extruded beneath
the water, characterized by glassy pillows filled
with crystalline basalt
Fig. 6.2
Vesicular Basalt:
trapped gases form bubbles (vesicles)
Fig. 6.3
Fig. 6.4
Volcanic Bomb
Pyroclastic
Material:
Fragmentary
volcanic rocks
ejected into the
air
Fig. 6.5
Pyroclastic Flows:
A density flow consisting
of a hot (up to 800o C),
poisonous mixture of gas
and pyroclastic material
moving downslope at
speed in excess of 200
km/hr!
Fig. 6.8
Fig. 6.6
Volcanic Features Formed by
Central Eruptions
•
•
•
•
•
•
Shield Volcanoes
Volcanic domes
Cinder-cones Volcanoes
Composite Volcanoes
Craters
Calderas
Eruptive Styles and Landforms
Mauna Kea
Shield Volcano
Volcanic Dome
Mauna Loa
Cinder Cone
Volcano
Composite
Volcano
Crater
Caldera
Fig.6.9.a
Fig. 6.9
Shield Volcano
Lava
Dome
Fig.
6.9b
Fig.6.9.a
Lyn Topinka/USGS
Volcanic Dome
Cerro Negro
Cinder Cone,
near
Managua,
Nicaragua
in 1968
Fig. 6.9b
Mark Hurd Aerial Surveys
Fig. 6.9c
Mt Fujiyama, Japan
Cinder Cone
Fig. 6.9c
Raga/The Stock Market
Fig. 5.15
Caldera
Stages in the
Development
of
Crater Lake
Fig. 6.10
Shiprock,
Formation of a Diatreme
New Mexico
Fig. 6.12
Fig. 6.12
Fissure Eruptions
A volcanic eruption originating
along an elongate fissure rather
than a central vent.
Volcanoes along
the Laki Fissure
(Iceland) formed
in 1783, resulting
in the largest lava
flow in recorded
history
Fig. 6.13
Mt. St. Helens: Before
Hydrothermal Activity:
• The circulation of water through hot
volcanic rocks and magma
• Forms fumaroles – volcanic vents
emitting gases, some charged with
dissolved minerals
• Forms geysers – heated
hydrothermal waters under
pressure, that intermittently erupts at
the surface
• Provides the source for Geothermal
Energy.
Mt. St. Helens: During
Sulfur-encrusted Fumarole
Fig. 6.16
Volcanism Associated with Plate Tectonics
Fig. 6.19
Fig. 6.20