Volcanoes and Volcanic Landforms

1
THE ROCK CYCLE
2
VOLCANISM
3
I. Introduction

• From Roman god of fire Vulcan

4
I. Introduction

• From Roman god of fire Vulcan
• What is a volcano
• A conical mountain formed around a vent where
  lava pyroclastic materials and gases are
  erupted.

5
I. Introduction

• B. Volcanic activity
• Active
• Dormant
• Extinct

6
B. Volcanic Activity

• 1. Active volcanoes
• activity in the last few centuries
• Ex Vesuvius 79 A.D.
• (50 times in 2000 yr)
• Ex Mt. St. Helens (1980)

7
B. Volcanic Activity

• 2. Dormant volcanoes
• quiet for the last hundred to thousands of
  years but still have potential to erupt.
• Mt. Rainier

8
B. Volcanic Activity

• 3. Extinct volcanoes
• No eruption in historical times
• No signs of erupting again

9
Introduction C. Volcano Distribution

• Most volcanoes occur in one of three areas
• Circum-Pacific (i.e. The Ring of Fire)
• 60
• Mediterranean
• 20
• Spreading centers
• 10 15

10
Volcano Distribution
11
II. Volcanic materials

• Three types of material expelled from volcanoes

12
Volcanic materials

• A. Lava (the liquid)
• Molten rock

13
Volcanic materials

• A. Lava
• Molten rock
• Si affects viscosity

14
II. Volcanic materials

• A. Lava
• 1) Pahoehoe lava
• Basaltic lava
• Low viscosity

15
II. Volcanic materials

• A. Lava
• 1) Pahoehoe lava
• Basaltic lava
• Low viscosity
• Cools moderately slowly
• Ropelike appearance

16
II. Volcanic materials

• A. Lava
• 2) Aa lava (pronounced aa-aa)
• Basaltic lava
• Higher viscosity
• Solidifies while flowing
• Angular pieces

17
II. Volcanic materials

• A. Lava
• 3) Pillow lavas
• Lava extruded underwater
• Cools and contracts
• Spherical masses
• Ocean floor

18
II. Volcanic materials

• A. Lava (the liquid)
• B. Ash and pyroclastic material (the solid)
• Airborne material ejected by a volcano
• Classified based on size

19
B. Ash and pyroclastic material (the solid)

• Volcanic ash
• Fine ash - lt0.06mm
• Coarse ash 0.06mm to 2mm
• Composition rock mineral and volcanic glass

20
B. Ash and pyroclastic material (the solid)

• Cinders
• 2 mm and 64 mm
• Composition - same as ash
• Hazardous when falling

21
B. Ash and pyroclastic material (the solid)

• C) Bombs
• Larger than 64mm
• Molten rock solidifies in the air
• Shapes vary

22
II. Volcanic materials

• C. Volcanic gases (the gases)
• Volatiles
• H2S Hydrogen sulfide
• H2O Water vapor
• SO2 Sulfides
• CO2 Carbon dioxide
• N2 Nitrogen
• HCl Hydrochloric Acid
• Significance

23
II. Volcanic materials

• A) Determines violence of an eruption
• High gas violent eruptions
• Violent eruptions felsic magmas
• High viscosity magma traps gas
• Expansion is prevented pressure builds

24
II. Volcanic materials

• B) Effects on global climate
• CO2 Greenhouse gas
• SO2 Blocks sunlight

25
II. Volcanic materials

• Hazards to humans
• Clouds of CO2 get released
• Travels across the ground

26
III. Volcanic Landforms
27
III. Volcanic Landforms

• An erupting volcano will produce a number of
  distinct landforms including
• A. Volcanic cones
• B. Flood basalts
• C. Calderas

28
A. Volcanic cones

• Three types of volcanic cones

29
A. Volcanic cones

• 1) Shield volcanoes
• Multiple layers of basaltic lava
• Shallow sides due to magmas low viscosity
• Gentle eruptions

30
A. Volcanic cones

• 1) Shield volcanoes
• Tall volcanoes 3 or 4 miles tall
• Wide base Diameter of ten of miles

31
A. Volcanic cones

• Mauna Loa volcano Hawaii

32
A. Volcanic cones

• 2) Cinder cones
• Smallest volcanic cone
• Layered ash and cinders
• Ex El Paricutin

33
A. Volcanic cones

• 2) Cinder cones
• Short narrow cone
• Steep sides
• Violent eruptions

34
A. Volcanic cones

• Lassen National
• Monument CA

35
A. Volcanic cones

• 3) Composite or stratovolcanoes
• Layered ash lava and mud
• Intermediate to felsic lava
• Steep sides due to lavas high viscosity

36
A. Volcanic cones

• 3) Composite or stratovolcanoes
• Tall volcanoes 1 to 2 miles high
• Violent eruptions

37
A. Volcanic cones

• Mt. St. Helens
• WA

38
III. Volcanic Landforms B) Flood basalts

• Large outpourings of basaltic lava
• Multiple quiet eruptions
• Lava plateau

39
B) Flood basalts

• A portion of the Columbia Flood Basalts in WA

40
III. Volcanic Landforms

• C) Calderas
• Large depressions (gt 1km) from violent eruptions
• Ugashik Caldera AK

41
C) CalderasTwo methods of formation

• Method 1
• Volcano rapidly empties its magma chamber and
  support is lost

42
C) Calderas

• Method 1 (cont.)
• Overlying material collapses into magma chamber
• Caldera forms

43
C) Calderas

• Ex Crater Lake
• OR

44
C) CalderasTwo methods of formation

• Method 2
• Volcano blows its top
• leaving behind a void
• Inside the cone.

45
C) CalderasTwo methods of formation

• Method 2
• Volcano blows its top
• leaving behind a void
• Inside the cone.

46
IV. Volcanic hazards
47
IV. Volcanic hazards

• Lahars (hot mud flows)

48
IV. Volcanic hazards

• Lahars
• Sources of water
• Melting ice caps
• Excess rainfall

49
IV. Volcanic hazards

• B) Nuee Ardentes (Glowing Ash flows)
• Clouds of dense gas and debris
• French for glowing cloud
• High speeds and high temperatures

50
IV. Volcanic hazards

• How does a Nuee Ardente form
• Volcano erupts
• Hot debris rises
• Gravity takes over

51
IV. Volcanic hazards

• How does a Nuee Ardente form(contd)
• Debris descends rapidly (200 mph)
• Flows down mountain slopes
• Travel up to 80 miles

52
IV. Volcanic hazards

• C) Tsunamis
• Wave generated by volcanic explosion
• Japanese for harbor wave

53
IV. Volcanic hazards

• Tsunamis are extremely hazardous
• Travel vast distances
• Strike with short notice
• Krakatoa (1883) - 36000 people died

54
IV. Volcanic hazards

• D) Lava flows
• Least dangerous
• Lava flows slowly (lt10 mph)
• Dangerous to property

55
V. Predicting Eruptions

• Why try to predict eruptions
• Minimize damage
• Minimize loss of life
• Four ways to predict an eruption

56
V. Predicting Eruptions

• 1) Harmonic tremors
• Small earthquakes
• From moving magma
• Last for hours

57
V. Predicting Eruptions

• 2) Increased gas emissions
• CO2
• SO2
• H2S
• Large tracts of healthy forests die off

58
V. Predicting Eruptions

• 3) Changes in mountain shape
• Pressure from the magma deforms the mountain
• Detected by tiltmeters

59
V. Predicting Eruptions

• Tiltmeter
• Tiltmeter measures ground tilt
• Stable ground zero tilt
• Change from zero indicates shape change

60
V. Predicting Eruptions

• Mt. St. Helens and the orange line

61
V. Predicting Eruptions

• 4) Observe material from past eruptions
• Geologists map out past
• Lahars
• Lava flows
• Count number of past eruptions
• Date each eruption
• Calculate periodicity

62
VI. Benefits of Volcanoes

• Benefits of volcanoes
• Soils
• Energy from heat
• Rock (Pumice)
• Gases for industry