The Nature of Volcanic Eruptions Magmas Composition Temperature

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The Nature of Volcanic Eruptions

The Nature of Volcanic Eruptions

 • Magma’s Composition • Temperature • Dissolved Gases

• Magma’s Composition • Temperature • Dissolved Gases

Mobility or Viscosity (viscos=sticky)

Mobility or Viscosity (viscos=sticky)

 The more viscous the material, the greater its resistance to flow Magma’s viscosity

The more viscous the material, the greater its resistance to flow Magma’s viscosity is due to its silica content Silica impedes the flow of magma because silicate structures start to link together The more silica in magma the greater the viscosity Amount of volatiles (gaseous component, mainly water) affects the mobility of magma Rhyolitic (felsic lavas) – very viscous, form thick short, thick flows Basaltic lavas – more fluid, travel up to 150 km

�Temperature �Chemical Composition Factors affecting Viscosity

�Temperature �Chemical Composition Factors affecting Viscosity

Why do volcanoes erupt?

Why do volcanoes erupt?

 Most magma is generated by partial melting in the upper mantle to form

Most magma is generated by partial melting in the upper mantle to form molten material (basaltic) Once formed the buoyant molten rock rises to the surface Density of crustal rocks decreases when closer to the surface, ascending basaltic magma may reach a level where rocks are less dense Formation of a magma chamber occurs As magma body cools, minerals with high temperatures crystallize first, leaving remaining melt enriched in silica. Some molten Material may ascend to the surface to produce a volcanic eruption

Hawaiian Type Eruptions

Hawaiian Type Eruptions

 • Magma mobilizes and quickly moves upward along the newly buoyant plumes called

• Magma mobilizes and quickly moves upward along the newly buoyant plumes called eruption columns that extends thousands of meters in the atmosphere • Bubbles grow by - continued separation of gases from the melt - expansion of bubbles as confining pressure drops

� Volatiles tend to be most abundant near tops of magma reservoirs containing silica

� Volatiles tend to be most abundant near tops of magma reservoirs containing silica rich melts � Viscosity of magma + dissolved gases = nature of volcanic eruption � Basaltic magmas – smaller gaseous component and permit fluid and gentle flow of lava � Silica-Rich magmas – more gaseous component, explosive

MATERIALS EXTRUDED DURING AN ERUPTION

MATERIALS EXTRUDED DURING AN ERUPTION

Volcanoes extrude : vlava vlarge volumes of gas vpyroclastic materials

Volcanoes extrude : vlava vlarge volumes of gas vpyroclastic materials

v. Lava Flows Ø Lava - is molten rock that flows out of volcanoes

v. Lava Flows Ø Lava - is molten rock that flows out of volcanoes Ø CATEGORIES OF LAVA : 1. Basaltic - is comprised of the least amount of silica. It is the fastest flowing lava. Basaltic lava is commonly expelled from shield volcanoes. 2. Andesitic - It has a higher viscosity than basaltic lava and thus flows at a slower rate. Its flow is described as block flow. 3. Rhyolitic - has the highest viscosity, It flows much slower than andesitic and basaltic lava.

Basaltic Lava Andesitic Lava Ryolitic Lava

Basaltic Lava Andesitic Lava Ryolitic Lava

Two Types of Lava Flows : aa Flows have surfaces of rough jagged blocks

Two Types of Lava Flows : aa Flows have surfaces of rough jagged blocks with dangerously sharp edges and spiny projections. Pahoehoe Flows exhibit smooth surfaces that often resemble the twisted braids of ropes. Pahoehoe means “on which one can walk. ”

Lava Tubes v. Hardened basaltic flows commonly contain cave-like tunnels that were once conduits

Lava Tubes v. Hardened basaltic flows commonly contain cave-like tunnels that were once conduits carrying lava from the volcanic vent to the flow’s leading edge. v. Lava tubes are important features because they serve as insulated pathways that facilitate the advance of lava great distances from its source.

GASE S q Magmas contain varying amounts of dissolved gases(volatiles) held in the molten

GASE S q Magmas contain varying amounts of dissolved gases(volatiles) held in the molten rock by confining pressure. q The gaseous portion of most magmas makes up from 1 to 6 percent of the total weight, with most of this in the form of water vapor.

Pyroclastic Materials • When volcanoes erupt energetically they eject pulverized rock, lava, and glass

Pyroclastic Materials • When volcanoes erupt energetically they eject pulverized rock, lava, and glass fragments from the vent. • The particles produced are referred to as pyroclastic materials (pyro = fire, clast = fragment)

Volcanic Ash Block Scoria Welded Tuff Lapilli Bomb Pumice

Volcanic Ash Block Scoria Welded Tuff Lapilli Bomb Pumice

Volcanic Structures and Eruptive Styles

Volcanic Structures and Eruptive Styles

ANATOMY OF A VOLCANO

ANATOMY OF A VOLCANO

Types of Volcanoes Shield volcano • Broad, slightly domed-shaped/ resembles a Warrior's shield •

Types of Volcanoes Shield volcano • Broad, slightly domed-shaped/ resembles a Warrior's shield • Composed primarily of basaltic lava • Generally cover large areas • Produced by mild eruptions of large volumes of lava

Mauna Loa : A Classic Shield Volcano

Mauna Loa : A Classic Shield Volcano

Kilauea, Hawaii : Eruption of a Shield Volcano

Kilauea, Hawaii : Eruption of a Shield Volcano

Cinder cone • Built from ejected lava (mainly cinder-sized) fragments • Steep slope angle

Cinder cone • Built from ejected lava (mainly cinder-sized) fragments • Steep slope angle • Rather small size • Frequently occur in groups

Paricutin: Life of a Garden-Variety Cinder Cone

Paricutin: Life of a Garden-Variety Cinder Cone

Composite cone (Stratovolcano) • Most are located in a relatively narrow zone that rims

Composite cone (Stratovolcano) • Most are located in a relatively narrow zone that rims the Pacific Ocean, appropriately called the Ring of Fire. • Large, classic-shaped volcano (1000’s of ft. high & several miles wide at base) • Composed of interbedded lava flows and layers of pyroclastic debris.

Fujiyama , Japan

Fujiyama , Japan

Nuée Ardente: A Deadly Pyroclastic Flow • Pyroclastic flows, which consist of hot gases

Nuée Ardente: A Deadly Pyroclastic Flow • Pyroclastic flows, which consist of hot gases infused with incandescent ash and larger lava fragments. Also referred to as nuée ardentes (glowing avalanches), these fiery flows are capable of racing down steep volcanic slopes at speeds that can exceed 200 kilometers (125 miles)per hour.

Mt. Mayon

Mt. Mayon

In addition to violent eruptions, large composite cones may generate a type of very

In addition to violent eruptions, large composite cones may generate a type of very fluid mudflow referred as lahar. These destructive flows occur when volcanic debris becomes saturated with water and rapidly moves down steep volcanic slopes, generally following gullies and stream valleys.

Other Volcanic Landforms • Calderas (caldaria. = a cooking pot) are large depressions with

Other Volcanic Landforms • Calderas (caldaria. = a cooking pot) are large depressions with diameters that exceed one kilometer and have a somewhat circular form. Calderas are formed by the following processes: (1) Crater Lake-type calderas (2) Hawaiian-type calderas (3) Yellowstone-type calderas

Fissure Eruptions and Basalt Plateaus • The greatest volume of volcanic material is extruded

Fissure Eruptions and Basalt Plateaus • The greatest volume of volcanic material is extruded from fractures in the crust called fissures (fissure: = to split).

Volcanic pipes and necks • Pipes are short conduits that connect a magma chamber

Volcanic pipes and necks • Pipes are short conduits that connect a magma chamber to the surface • Volcanic necks are resistant vents left standing after erosion has removed the volcanic cone

Shiprock, NM – a volcanic neck

Shiprock, NM – a volcanic neck

Intrusive igneous activity

Intrusive igneous activity

Tabular intrusive bodies • Dikes – forms when rising magma vertically cuts across the

Tabular intrusive bodies • Dikes – forms when rising magma vertically cuts across the sedimentary beds • Sills _ forms when magma enters through a weak portion of the sedimentary bed horizontally

Massive intrusive bodies • Batholiths – intrusive rocks that exposure of over 100 square

Massive intrusive bodies • Batholiths – intrusive rocks that exposure of over 100 square kilometers have a surface • Stocks – similar to a batholite but has less surface exposure. • Laccoliths – happens when rising magma lifts up the sedimentary bed that it penetrated.

Origins of Magma

Origins of Magma

From solid rocks • Increase in temperature • Decompression Melting • Addition of Volatiles

From solid rocks • Increase in temperature • Decompression Melting • Addition of Volatiles

Partial Melting and Magma Compositions • As rocks are heated minerals with lower melting

Partial Melting and Magma Compositions • As rocks are heated minerals with lower melting points melt first, melted rocks that turn into magma then melts other rocks that have higher melting points.

Plate Tectonics and Volcanic Activity

Plate Tectonics and Volcanic Activity

 • Volcanism at Convergent Plate Boundaries • Volcanism at Divergent Plate Boundaries •

• Volcanism at Convergent Plate Boundaries • Volcanism at Divergent Plate Boundaries • Intraplate Volcanism

Living with Volcanoes

Living with Volcanoes

Volcanic Hazards • Pyroclastic flows • Lahars • Explosive eruptions

Volcanic Hazards • Pyroclastic flows • Lahars • Explosive eruptions

Monitoring Volcanic Activity • Changes in the pattern of volcanic earthquakes • Expansion of

Monitoring Volcanic Activity • Changes in the pattern of volcanic earthquakes • Expansion of near-surface magma chambers

 • Changes in the amount of gases that are released • Increase in

• Changes in the amount of gases that are released • Increase in ground temperature

FAULTS AND FRACTURES

FAULTS AND FRACTURES

FAULTS AND FRACTURES • Faults are fractures in the crust along which appreciable displacement

FAULTS AND FRACTURES • Faults are fractures in the crust along which appreciable displacement has taken place. • Is a fracture or zone of fractures between two blocks of rocks

TYPE OF FAULTS

TYPE OF FAULTS

DIP SLIP OR NORMAL SLIP

DIP SLIP OR NORMAL SLIP

STRIKE SLIP FAULTS

STRIKE SLIP FAULTS

THRUST FAULT

THRUST FAULT

Continental Collisions

Continental Collisions

Continental Collisions results in the development of mountains characterized by shortened and thickened crust

Continental Collisions results in the development of mountains characterized by shortened and thickened crust achieved through folding and faulting.

The Himalayas are the youngest collision mountains on Earth and are still rising. (India

The Himalayas are the youngest collision mountains on Earth and are still rising. (India began to collide with Asia)

Shilla Peak in the Himalayas, northeastern Himachal Pradesh State, India Himalayas Glaciers: Zaskar Range

Shilla Peak in the Himalayas, northeastern Himachal Pradesh State, India Himalayas Glaciers: Zaskar Range of Jammu and Kashmir State, Northern India

The collision between India and Asia that generated the Himalayas and Tibetan Plateau also

The collision between India and Asia that generated the Himalayas and Tibetan Plateau also severely deformed much of Southeast Asia. a. ) Map view of some of the major structural features of Southeast Asia thought to be related to this episode of mountain building. b. ) Re-creation of the deformation of Asia, with a rigid block representing India pushed into a mass deformable modeling clay.

The Appalachians indicates that the formation of this mountain belt was complex and resulted

The Appalachians indicates that the formation of this mountain belt was complex and resulted from three distinct episodes of mountain building.

Three Episodes of Mountain Building 1. Taconic Orogeny – the collision that ensued between

Three Episodes of Mountain Building 1. Taconic Orogeny – the collision that ensued between 450 and 500 million years ago. Deformed the continental shelf and sutured the crustal fragment to the North American Plate. The metamorphosed remnants of the continent fragment are recognized today as the crystalline rocks of the Blue Ridge and Western Peidmont regions of the Appalachians. 2. Acadian Orogeny – began about 400 million years ago. The continued closing of the ancestral North Atlantic resulted in the collision of the developing island arc with North America. 3. Final Orogeny – between 250 and 300 million years ago, when Africa collided with America.

CRUSTAL DEFORMATION AND MOUNTAIN BUILDING

CRUSTAL DEFORMATION AND MOUNTAIN BUILDING

CRUSTAL DEFORMATION

CRUSTAL DEFORMATION