1. The Nature of Volcanic Eruptions
Viscosity

2. Magma’s Composition
Temperature
Dissolved Gases

3. Mobility or Viscosity (viscos=sticky)

4. 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 150km

5. Factors affecting Viscosity
Temperature
Chemical Composition
Factors affecting Viscosity

6. Why do volcanoes erupt?

7. 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

9. Hawaiian Type Eruptions

10. 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

11. 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

12. MATERIALS EXTRUDED DURING AN ERUPTION

13. pyroclastic materials
lava
large volumes of gas
pyroclastic materials
Volcanoes extrude :

14. Lava Flows Lava - is molten rock that flows out of volcanoes
CATEGORIES OF LAVA :
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.
Lava is the molten rock expelled by a volcano during an eruption. The resulting rock after solidification and cooling is also called lava. The molten rock is formed in the interior of some planets, including Earth, and some of their satellites.The vast majority of lava on Earth, more than 90 percent of the total volume, is estimated to be basaltic in composition.

15. Basaltic Lava Andesitic Lava
Ryolitic Lava

16. 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.”
Aa and pahoehoe lavas can erupt from the same vent. However, pahoehoe lavas form at higher temperatures and are more fluid than aa flows. In addition, a pahoehoe lava flow can change into an aa lava flow, although the reverse (aa to pahoehoe) does not occur.

17. Lava Tubes
Hardened basaltic flows commonly contain cave-like tunnels that were once conduits carrying lava from the volcanic vent to the flow’s leading edge .
Lava tubes are important features because they serve as insulated pathways that facilitate the advance of lava great distances from its source.
A lava tube is a natural conduit formed by flowing lava which moves beneath the hardened surface of a lava flow. Lava tubes can be actively draining lava from a volcano during an eruption, or can be extinct, meaning the lava flow has ceased and the rock has cooled and left a long, cave-like channel. Lava flows often develop a solid crust while the molten lava below continues to advance in conduits called lava tubes. View of an active lava tube as seen through the collapsed.

19. GASES
Magmas contain varying amounts of dissolved gases(volatiles) held in the molten rock by confining pressure.
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.
Obtaining gas samples from an erupting volcano is difficult and dangerous, so geologists usually must estimate the amount of gas originally contained within the magma. Occasionally, eruptions emit colossal amounts of volcanic gases that rise high into the atmosphere, where they may reside for several years. another.) Sulfur compounds are easily recognized by their pungent odor. Volcanoes are also natural sources of air pollution—some emit large quantities ofsulfur dioxide, which readily combines with atmospheric gases to form sulfuric acid and other sulfate compounds.

21. 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)
A pyroclastic flow is a fluidized mixture of solid to semi-solid fragments and hot, expanding gases that flows down the flank of a volcanic edifice. These awesome features are heavier-than-air emulsions that move much like a snow avalanche, except that they are fiercely hot, contain toxic gases, and move at phenomenal, hurricane-force speeds, often over 100 km/hour. They are the most deadly of all volcanic phenomena.

22. Volcanic Ash Welded Tuff Lapilli Block Bomb Scoria Pumice
Ash and dust particles are produced when gas-rich viscous magma erupts explosively.
When the hot ash falls, the glassy shards often fuse to form a rock called welded tuff.
Lapilli - walnut-sized material
Blocks - hardened or cooled lava
Bombs - ejected as hot lava
scoria – is the name applied to vesicular ejecta that is a product of basaltic magma
Pumice-is usually lighter in color and less dense than scoria, and many pumice fragments have so many vesicles that they are light enough to float.
Scoria
Pumice

23. Volcanic Structures
and
Eruptive Styles

24. ANATOMY OF A VOLCANO Opening at the summit of a volcano
Anatomy of a "typical" composite cone .
Volcanic activity frequently begins when a fissure (crack) develops in the crust as magma moves forcefully toward the surface. As the gas rich magma moves up through a fissure, its path is usually localized into a circular conduit, or pipe, that terminates at a surface opening called a vent.
General Features
Opening at the summit of a volcano
Crater - steep-walled depression at the summit, generally less than 1 km diameter
Caldera - a summit depression typically greater than 1 km diameter, produced by collapse following a massive eruption
Vent – opening connected to the magma chamber via a pipe

25. 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
Shield volcano
Broad, slightly domed-shaped
Composed primarily of basaltic lava
Generally cover large areas
Produced by mild eruptions of large volumes of lava
Mauna Loa on Hawaii is a good example

26. Mauna Loa : A Classic Shield Volcano

27. Kilauea,Hawaii : Eruption of a Shield Volcano
the most active and intensely studied shield volcano in the world, is located on the island of Hawaian the shadow of Mauna Loa.More than 50 eruptions have been witnessed here since record keeping began in Several months before each eruptive phase, Kilauea inflates as magma gradually migrates upward and accumulates in a central reservoir located a few kilometers below the summit.

28. Cinder cone Built from ejected lava (mainly cinder-sized) fragments
Steep slope angle
Rather small size
Frequently occur in groups
cinder cones (also called scoria cones)
are built from ejected lava fragments that take on the appearance of cinders or clinkers as they begin to harden in flight. These pyroclastic fragments range in size from fine ash to bombs that may exceed a meter in diameter. However, most of the volume of a cinder cone consists of pea- to walnut-sized lapilli that are markedly vesicular and have a black to reddish brown color. Although cinder cones are composed mostly of loose pyroclastic material, they sometimes extrude lava. On such occasions the discharges most often come from vents located at or near the base rather than from the summit crater.

29. Paricutin: Life of a Garden-Variety Cinder Cone
One of the very few volcanoes studied by geologists from its very beginning is the cinder cone called Paricutin, located about 320 kilometers(200miles) west of Mexico City. In 1943 its eruptive phase began in a cornfield owned by Dionisio Pulido, who witnessed the event as he prepared the field for planting.

30. 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.
Earth’s most picturesque yet potentially dangerous volcanoes are composite cones or strato volcanoes. Most are located in a relatively narrow zone that rims the Pacific Ocean, appropriately called the Ring 0f Fire.

31. Fujiyama , Japan
Japan's Fujiyama exhibits the classic form of a composite cone—steep summit and gently sloping flanks.

32. 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 (125miles)per hour.
NUÉE ARDENTES -- these contain dense lava fragments derived from the collapse of a growing lava dome or dome flow.
The French geologist Alfred Lacroix attached the name nuée ardente (glowing cloud) to the pyroclastic flow from Mt. Pelée that destroyed the city of St. Pierre in The flow was generated from the explosive collapse of a growing lava dome at the summit of the volcano, which then swept down on the city. Thus, nuée ardente eruptions are often called Peléen eruptions. However, this term cannot be as narrowly defined as the other eruption types, because nuée ardentes are often linked with both Plinian and Vulcanian activity.

33. Mt. Mayon

35. 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.

36. 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
CraterLake—Type Calderas CraterLake
Oregon, is situated in a caldera that has a maximum diameter of 10 kilometers (6 miles) and is 1,175 meters (more than 3,800 feet) deep. This caldera formed about 7,000 years ago when a composite cone, later named Mount Mazama, violently extruded 50-'70 cubic kilometers of pyroclastic material
Hawaiian-Type Calderas
Although some calderas are produced by a collapse following an explosive eruption, many are not. For example, I—Iawaii’s active shield volcanoes, Mauna Loa and Kilauea, both have large calderas at their summits
Yellowstone-Type Calderas
Historic and destructive eruptions such as Mount St.Helens and Vesuvius pale in comparison to what happened 630,000 years ago in there gi on now occupied by Yellowstone National Park, when approximately 1,000 cubic kilometers of pyroclastic material erupted.

37. Steep-walled depressions at the summit
Calderas
Steep-walled depressions at the summit
Size generally exceeds 1 km in diameter
Pyroclastic flows
Associated with felsic & intermediate magma
Consists of ash, pumice, and other fragmental debris

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

39. 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

41. Shiprock, NM – a volcanic neck

42. Intrusive igneous activity
There are two igneous activities: 1. extrusive 2. intrusive. The difference between the two is that extrusive igneous rock are igneous rock that are formed from lava while intrusive igneous rocks are formed when magma slowly crystallizes through time. * Magma can be called lava when it is on the outside of the volcano.
* Magma rises when it is less dense than its surrounding rocks.

43. 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
There are two classifications of intrusive igneous rocks: 1. tabular 2. massive. In the tabular intrusive bodies there are two subcategories: the dikes and the sills. Dikes are formed when magma vertically penetrates the layers of rocks above it but unsuccessfully reaches the surface, which eventually crystalizes.
Sills are formed when magma is injected between weak sedimentary bed layers. Sills penetrate horizontally.

44. Massive intrusive bodies
Batholiths – intrusive rocks that have a surface exposure of over 100 square kilometers
Stocks – similar to a batholite but has less surface exposure.
Laccoliths – happens when rising magma lifts up the sedimentary bed that it penetrated.
Massive intrusive bodies have 3 subcategories: the batholiths, the stocks and the laccoliths.
Batholiths are formed when magma chambers begin to cool down and crystalize through time. Batholiths are the largest intrusive bodies that have a surface exposure area of more than 100 square kilometers when eroded.
Stocks are batholiths that have a surface exposure are of less than 100 square kilometers when eroded.
Laccoliths form when magma is injected or penetrates through the layers of rocks and starts to inflate the layer with magma forming a mushroom shaped chamber.

45. Igneous bodies before they crystalize
Igneous bodies before they crystalize. Magmas start to rise and penetrate through layers of rocks.

46. Magma hardens turning them into intrusive or plutonic igneous rocks
Magma hardens turning them into intrusive or plutonic igneous rocks. Intrusive igneous rocks have a slower cooling process which leads to well-formed crystals such as Diorites, and Granites.

47. Because of extensive erosion intrusive igneous rocks become exposed.

48. Origins of Magma

49. From solid rocks Decompression Melting Increase in temperature
Addition of Volatiles
*Increase in temperature – as one goes deeper in the earth’s surface the temperature gets higher. This increase in temperature causes the rocks to melt turning into lava.
>The increase in temperature is called geothermal gradient
*Decompression Melting – the deeper the rock is in the earth’s surface the higher the pressure that is confining the rock. When pressure is high a rocks melting point also increases. Meaning rocks that are nearer the surface are more easier to melt which results into decompression melting.
*Addition of volatiles – addition of volatiles such as water and carbon dioxide can lower the rock melting point making it easier to melt. In deep pressure “wet” rocks are more likely to melt first than “dry” rocks.

50. 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.
*Rocks with low melting points melt first and become magma. If melting continues magma from the primary melted rocks melt the surrounding rocks with higher melting points. As more rocks are melted magma will steadily have an overall composition of a rock.

51. Plate Tectonics and Volcanic Activity

52. Volcanism at Convergent Plate Boundaries
Volcanism at Divergent Plate Boundaries
Convergent plate boundaries – when oceanic and continental plates converge the form volcanic arcs. Volcanoes that form may both be underwater or above ground.
>Volcanic Island Arc - are volcanoes underwater that grew large enough for them to rise above the surface level >Continental Volcanic Arc – are formed on the continental plates. Its lava is more viscous because of the thickness of the crust in the continental plates.
Divergent plate boundaries – magma generates from the mantle as two plates are being torn apart. Intraplate volcanism – occurs when there is a mass that is hotter than the normal mantle. That mass is called a mantle plume. It ascends towards the surface in a blob form, just like in lava lamps.
Intraplate Volcanism

53. An example of a mantle plume rising
An example of a mantle plume rising. As the mantle reaches the crust it begins its process of decompression melting.

54. Living with Volcanoes

55. Pyroclastic flows Lahars Explosive eruptions Volcanic Hazards
Pyroclastic Flows – it is a mixture of gas, ash and pumice that exceeds 800 degrees Celsius.
Lahar - a mixture of volcanic debris and water that flow downhill at a speed of 100 km/hr.
Explosive eruptions – send outs debris in a big area that can damage properties and lives.

56. Monitoring Volcanic Activity
Changes in the pattern of volcanic earthquakes
Expansion of near-surface magma chambers
Changes in volcanic earthquake patterns can be signs that a volcano is about to erupt or has become active again.
Expansion of near surface chambers is a sign that the roof of a volcano may rise as new magma is added in its interior.

57. Changes in the amount of gases that are released
Increase in ground temperature
Changes in the amount of gases that are released. Volcanologist monitor what gasses are released by the volcano and the amount the gas it has released. Some volcanoes drop their gas emission dramatically before erupting, just like the 1991 eruption of Mount Pinatubo.
Infrared sensors are used to detect the change in lava flow and volcanic columns that are rising inside the volcano .

69. Faults and Fractures

70. 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

71. TYPE OF FAULTS

72. DIP SLIP Or NORMAL SLIP

73. Strike slip faults

74. Thrust fault

75. Continental Collisions

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

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

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

79. 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.

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

82. Three Episodes of Mountain Building
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.

84. CRUSTAL DEFORMATION AND MOUNTAIN BUILDING

85. CRUSTAL DEFORMATION