Modules 1-4 PHY 120 Study Guide
Earth's Context in the Universe
The Earth's origin is part of the Solar System's history, which is in turn part of the Universe's history.
The Universe is vast and contains billions of galaxies:
Milky Way: Our galaxy, made up of over 250 billion stars.
Sun: A relatively small star among those in the Milky Way.
Earth: One of the 8 planets that orbit the Sun.
The Age and Formation of the Universe
Current Best Theory: The Big Bang Theory
Overall theory of cosmic evolution remains incomplete, but major elements align with observations.
Concept:
Matter was once concentrated at a single point of infinite density before exploding, leading to the formation of all space, time, matter, and energy.
Observations Supporting the Big Bang Theory
The Universe is expanding, as evidenced by Edwin Hubble's discovery in 1929:
Galaxies are moving apart, and their velocities are proportional to their distances from Earth, indicating that more distant galaxies recede faster than those nearby.
Doppler Shift
Concept: The change in pitch of a sound as an emergency vehicle passes is a manifestation of the Doppler shift.
Application to Light:
Light from distant objects can also exhibit Doppler shift:
When a star moves away, its light shifts toward the red end of the spectrum (redshift).
When it approaches, the light shifts toward the blue end (blueshift).
Significant Findings:
Early 20th-century researchers observed redshifts in galaxies, leading to Hubble's finding that the Doppler shift increases with distance, confirming the Universe's expansion.
Details of the Big Bang
Imagining galaxies moving apart and reversing the footage would show them merging at a single point, the birthplace of the Universe.
Process:
The Universe started expanding from a single point at unimaginable speeds.
As it expanded and cooled, hydrogen and helium formed, which gravity pulled together to create stars and galaxies.
Heavier elements, such as carbon and silicon, were formed in early stars through nuclear fusion and expelled into space upon stellar death.
Estimates indicate the Universe is about 13.8 billion years old based on redshift measurements, signifying that materials would have been at a single point during the Big Bang.
Formula used:
\text{Time since the Big Bang} = \frac{\text{separation distance}}{\text{recessional velocity}}
Note that the expansion rate fluctuated in history, motivating ongoing observations (e.g., the Webb telescope).
Cosmic Background Radiation
Post-Big Bang: 380,000 years later, electrons combined with nuclei, releasing photons with temperatures around 4000 K (visible red light).
As the Universe expanded over billions of years, this red light shifted to microwave radiation of approximately 2.7 K.
The Wilkinson Microwave Anisotropy Probe (WMAP) provides data on the universe's fundamental structure, indicating temperature fluctuations at 13.77 billion years old which correspond to the seeds that grew into galaxies.
Timeline of the Universe's Evolution
Big Bang to Reionization: 250 million years
First Stars: <180 million years
End of Cosmic Dark Ages: 380,000 years
Current Age of Universe: 13.8 billion years.
Concept Questions
Measurements of Doppler shift tell us:
a) The universe is expanding
b) Galaxies far away are moving away from us faster than closer galaxies
How old is the universe?
a) 13.8 billion years old
Formation of the Solar System
Formation Overview:
The orderly nature of the solar system suggests that all planets formed from the same primordial material as the Sun, approximately 4.56 billion years ago.
Nebular Hypothesis:
The Sun formed from a nebula caused by the collapse of a star (supernova).
Nebular Hypothesis Steps
Gravitational collapse of part of the giant molecular cloud resulted in rotation and contraction into a disk.
Most (90%) of the mass collected in the center, forming the Sun; the rest formed a protoplanetary disk.
Material segregated into rings around the Sun, where Earth and other planets formed through aggregation of materials within these rings.
Evidence for the Nebular Hypothesis
Meteorites:
Extraterrestrial objects captured by Earth's gravity, surviving reentry. They represent primitive material for the solar system, key to determining the solar nebula's components, with radiometric ages clustering around 4.54 billion years.
Types of Meteorites:
Stony Meteorites: Made of rocky material.
Iron Meteorites: Metallic.
Stony-Iron Meteorites: Mixture of rocky and metallic materials.
Solar System Planet Formation
The Sun initiates fusion, leading to the formation of inner terrestrial planets (heavy elements, a few lighter elements).
Giant outer planets are formed from volatiles (gases) pushed to the outer solar system by solar winds.
Planet formation occurred rapidly within 10 million years post-solar nebula condensation.
Characteristics of the Sun
The Sun, a continuous nuclear fusion reactor, is the primary energy source for the solar system:
Diameter: 1.5 million km (small star).
Contains 98.8% of the solar system's material (mainly hydrogen and helium).
Emits energy equivalent to burning about 25 billion pounds of coal per second.
Inner Rocky Planets
Mercury: Hot, fast (88 days around the Sun), thin atmosphere, weak magnetic field, heavily cratered.
Venus: Similar density and gravity to Earth, extreme atmosphere with dense clouds and sulfuric acid.
Earth: Unique with liquid water abundance at the surface.
Mars: Evidence suggests earlier wetter, warmer conditions; mass is 1/3 of Earth.
Asteroid Belt
Location: Between Mars and Jupiter, consisting of planetary debris that never formed into a planet due to Jupiter's gravitational influence.
Outer Jovian Planets
Jupiter: Largest planet, gas giant of hydrogen, helium, methane, and ammonia; rapid rotation leads to atmospheric bands.
Saturn: 2nd largest, primarily hydrogen and helium, low density, characterized by its extensive rings.
Uranus and Neptune: Ice giants with similar sizes and atmospheres, unique tilt in Uranus possibly due to impact.
Data & Diagrams on Planetary Formation
Graphs illustrate relationships between distance from the Sun and resulting planetary temperatures at formation, determining the types of atoms bonding to form planets.
Earth's Formation and Differentiation
Early Earth: Characterized by high temperature and widespread impacts; heat generated by both protoplanets and radioactive isotopes resulted in a molten state.
Moon Formation: About 50 million years after Earth's initial accretion, a Mars-sized body collided with Earth, ejecting material that formed the Moon and adding heat, causing the planet's rotational speed to increase and tilting its axis approximately 23 degrees.
Differentiation Process:
Heat from collisions and radioactive decay caused differentiation whereby dense materials sank to the center, forming a core of iron and nickel while lighter elements formed the mantle and crust.
This significant event allowed for the formation of continents, oceans, and atmosphere.
Formation of Earth's Atmosphere and Oceans
Early Atmosphere: Initially similar to the Sun's composition (hydrogen and helium) was quickly lost due to weak gravity and impacts from the moon-forming body.
Second Atmosphere: Formed due to volcanic eruptions and external contributions from comets and asteroids, primarily consisting of water vapor, carbon dioxide, nitrogen, and little oxygen.
Current composition reflects significant changes over time driven by biological processes and geological activity.
Water Origins and Formation of Oceans
Evidence indicates oceans existed about 4.4 billion years ago, formed by water vapor condensation and contributions from comet impacts.
Earth's Interior Structure and Study Methods
Compositional Layers of Earth's Interior
Summary of Layers
Crust:
Composition:
Silicon (28%), Aluminum (8%), Iron (6%), Magnesium (4%), Calcium (2.4%), Other (5.6%), Oxygen (46%)
Average Density: ~2.7 g/cm³
Mantle:
Composition:
Silicon (21%), Aluminum (2.4%), Iron (6.3%), Magnesium (22.8%), Calcium (2.5%), Oxygen (44%)
Average Density: ~3.3 g/cm³
Outer Core:
Composition:
Nickel (6%), Iron (94%)
Density Range: 10 - 12 g/cm³
Inner Core:
Composition: Primarily Iron
Average Density: ~13 g/cm³
The Core
Description:
An iron-rich sphere with a radius of 3,471 km
Divided into:
Inner Core (Radius = 1,220 km): Solid sphere due to immense pressure.
Outer Core (2,255 km thick): Liquid layer.
Composition of Core:
Material: Iron-nickel alloy with minor components such as oxygen, silicon, and sulfur.
Density and Temperature:
Inner Core Density: 13 g/cm³
Outer Core Density: 10 - 12 g/cm³
Temperature of Inner Core: Approximately 6,000 °C (similar to the surface of the sun).
Core Rotation and Convection
Both inner core and outer core are spinning.
The heat from the inner core causes convection in the outer core, contributing to the generation of electric currents, which in turn create the Earth's magnetic field.
Evidence for Outer Core Convection
The presence of Earth's magnetic field indicates the movement of molten iron within the core, generating an electrical current.
The magnetic field acts as a magnetic dipole similar to a bar magnet.
Magnetic Pole Reversals
Definitions:
Secular Variation: Movement of magnetic poles geographically over time.
Spontaneous Reversals: Infrequent flips of the north and south magnetic poles.
Evidence for Pole Reversal:
Thermoremanent Magnetization: Rocks forming under specific conditions preserve their magnetic orientation, which aids in understanding historical magnetic conditions.
Paleomagnetic Time Scale: Recorded history of magnetic pole reversals.
The Mantle
Description:
Solid rock layer between the crust and the core, approximately 2,885 km thick (82% of Earth’s volume).
Composition: Predominantly ultramafic rock called peridotite.
Convection: Slow movement of mantle material; hot mantle rises while cold mantle sinks, leading to tectonic plate movements.
Subdivisions:
Upper Mantle: Cool and brittle (50 – 120 km thick).
Transitional Mantle: Ductile behavior extending up to 400 km.
Lower Mantle: Denser and hotter.
Behavior of the Mantle
The mantle can behave like a solid and a viscous fluid depending on the time scale.
Examples:
Glaciers: Flow slowly over time, but shatter when struck hard.
Silly Putty: Flows slowly but hardens or breaks with impact.
The Crust
Description: Thin, rocky outer layer with varying thickness.
Two Types of Crust:
Continental Crust: Average thickness of 35 – 40 km (up to 70+ km in mountain ranges), made up of a variety of rock types.
Oceanic Crust: Mainly igneous rock (basalt), with an average thickness of 7 – 10 km.
Density Comparison: Continental crust has a density of approximately 2.7 g/cm³ compared to oceanic crust's density of about 3 g/cm³.
Crust Characteristics
Buoyancy: The massive continental crust floats on the mantle, leading to its greater thickness compared to oceanic crust.
Regions of high elevation typically associated with thicker crust; oceanic crust is denser and thinner, thus sits lower than sea level.
Layers of Earth: Composition vs. Behavior
** compositional Layers:** Core, mantle, and crust respectively characterized by their materials.
Behavioral Layers: Lithosphere (solid and brittle) vs. Asthenosphere (ductile and capable of flow) based on physical properties.
Seismic Waves: Probing Earth's Interior
Body Waves: Includes P-waves and S-waves.
P-waves (Primary waves):
Compressional waves, fastest type of seismic wave, travel through solid and liquid.
Wave motion in the direction of travel causing material contraction and extension; speeds up to ~13,000 mph.
S-waves (Secondary waves):
Shear waves that move perpendicular to the direction of travel, cannot traverse through liquids, causing material to shear.
Slower than P-waves, with speeds around 9,000 mph.
Importance of Seismic Waves
Seismic waves help determine the Earth’s interior structure through their velocities and paths:
Changes in wave velocity indicate different density materials.
The presence or absence of S-waves can confirm solid or liquid states in various layers.
Shadow Zones
Areas where seismic waves are not recorded due to the change in material state (e.g., liquid outer core).
P-waves experience shadow zones at angles between 103° and 150°; S-waves are blocked, indicating core properties.
Studying Earth’s Structure
Seismic velocities are essential in determining the composition of Earth's layers and their properties.
Estimate Earth’s Average Density: ~5.5 g/cm³, indicating denser materials in the inner Earth to qualify for this average when factoring surface rock densities (2.0 to 2.7 g/cm³).
Plate Tectonics
History and Evidence of Plate Tectonics
Key Definitions
Tectonics: Movements of Earth’s lithosphere (crust + upper mantle).
Plate Tectonics: Movement of discrete segments of Earth’s lithosphere in relation to one another.
Continental Drift: Theory that continents move horizontally over the Earth's surface.
Major Features of Earth's Surface
Observations of major features:
Look for seafloor characteristics and formation methods.
Investigate disparity between eastern and western continental sides.
Understand the formation of underwater mountain ranges in oceans.
Explore explanations for high elevations in areas like the Himalayas.
Analyze the relationships between submarine trenches and geological activity (earthquakes/volcanoes).
Comprehend how geographical features like the Red Sea originated.
History of Plate Tectonics Theory
Initial skepticism and later acceptance of plate tectonics in geoscience.
Importance of scientific method in the development of the theory.
Learning Outcomes
After this lecture, one should be able to:
Describe evidence supporting the idea that continents were once joined.
Define what a tectonic plate is.
Distinguish between the theory of plate tectonics and the concept of continental drift.
Explain the theory of plate tectonics and the driving forces behind it.
Describe observations confirming the theory of plate tectonics.
Evidence for Continental Drift
Continental Drift Hypothesis (1915): Proposed by Alfred Wegener, asserting that Pangaea existed around 180 million years ago.
Key Evidence:
Geometrical fit of continental edges (e.g., South America and Africa).
Distribution of similar fossils across disparate continents (e.g., Glossopteris, Mesosaurus, Lystrosaurus).
Geological similarities in rock formations in South America and Africa.
Connectivity of mountain chains across continents.
Analysis of historical climate indicators (e.g., glacial deposits).
Fossil Evidence
Unique fossils found on separate continents show previous land connections.
If continental drift didn't occur:
Species evolved separately, contradicting Darwin’s evolutionary theory.
Alternative migration theories (e.g., aquatic movement) lack support.
Geological Similarities
Identical rock sequences in Brazil and South Africa suggest simultaneous formation under equivalent conditions.
This anomaly indicates prior proximity of these landmasses.
Glacial Evidence
Glacial marks suggest prior land links among continents, with orientations indicating interconnectedness.
Glacial deposits found in now arid Southern regions imply significant climatic shifts after continental separation.
Paleoclimate Indicators
Evidence of tropical plant fossils in cold regions (e.g., Antarctica) and glacial formations in tropical climates indicates significant climate changes.
Such indicators bolster the case for prior continental unity.
Shift from Continental Drift to Plate Tectonics
Skepticism surrounding Wegener’s hypothesis due to a lack of a mechanism for continental movement.
Rejection of the continental drift hypothesis led to its classification as a failed theory, while laying groundwork for plate tectonics.
Renewed research in the 1950s provided substantial geological and oceanic evidence, revitalizing interest in continental displacement:
Recognition of ocean floor topography (mid-ocean ridges).
Studies on seismic activity patterns concentrated on oceanic terrains.
Documentation of magnetic field reversals and their long-term impacts.
Insights gained from drilling expeditions demonstrating patterns of ocean sedimentation.
Development of Plate Tectonics Theory
Chronological contributions to the theory's formation:
Recognition of plate movements (1596).
Correlation between rock types and fossils across continents (1858).
Mapping of the Atlantic Mid-Ocean Ridge (1872).
Discovery of radioactive heat in Earth’s interior (1896).
Conceptualization of convective mantle drives (1927).
Mid-ocean ridge recognition (1953) and subsequent naming of oceanic spreading mechanisms (Harry Hess, 1962).
Establishment of tectonic plate-driven exhaustion of lithosphere at oceanic trenches, necessitating a balanced recycling process.
Mid-Ocean Ridges and Sea Floor Spreading
Hypothesized as zones for new oceanic crust formation.
Observations confirm the following properties:
Mid-ocean ridges serve as underwater mountain belts and spreading centers.
Seismic waves propagate more slowly over ridge zones due to heat and potential partial melting.
Volcanoes beneath ridges corroborate crustal generation at these sites.
Age of Ocean Floors
Young rocks near mid-ocean ridges age progressively moving away, substantiating sea floor spreading
Average sediment thickness indicates general vitality and age of ocean basins (averaging 260 million years minimum).
Observations detail sediment deposition rates and continental crust transformations.
Paleomagnetism and Plate Movement
Paleomagnetic studies reveal historical magnetic orientation correlations with age.
Research suggests historical polarity reversals create magnetic stripes amidst mid-ocean ridges, a vital component for understanding plate movement.
Hot Spots and Their Geological Implications
Hotspot volcanic activity indicative of tectonic progression:
Formation of island chains (e.g., Hawaii) due to hot mantle plumes.
As tectonic plates traverse over these plumes, aligned volcanic formation accounts for directional plate motion tracking.
Evidence Gathering and Contemporary Techniques
Current methodologies including GPS installations track tectonic shifts accurately over time, highlighting relative plate displacements.
Continued investigations elucidate movement rates across tectonic plate boundaries, contributing essential data toward understanding dynamic geological interactions.
Conclusion and Summary of Plate Tectonics
The unifying theory of plate tectonics integrates frameworks supported by paleomagnetic data, geological observations, and fossil correlation.
Ongoing discoveries continue to refine knowledge and understanding of Earth's surface transformations over geologic time, firmly establishing the dynamic nature of our planet's lithosphere.
Tectonic Plates and Their Characteristics
Major Tectonic Plates
List of Major Plates:
Arabian Plate
Philippine Plate
Juan de Fuca Plate
Caribbean Plate
Cocos Plate
Pacific Plate
African Plate
Nazca Plate
South American Plate
Scotia Plate
Antarctic Plate
Australian-Indian Plate
Plate Movement and Speed
Speed Categories:
Less than 3 cm/year
3 to 9 cm/year
More than 9 cm/year
Characteristics
Plates fit together like interlocking puzzle pieces.
They consist of more than just continents, terminating where they meet other plates.
Located atop the upper mantle (asthenosphere).
Plate Boundaries and Processes
Introduction to Plate Boundaries
Game Plan:
Topics Covered:
Plate Boundaries
Divergent
Convergent
Transform
Processes at Plate Boundaries
Earthquakes
Volcanoes
Reminders/Announcements:
Module 2 Activity is available today; comments due by Wednesday 9/17.
Quiz 2 available today; due Thursday 9/18.
Material for the quiz includes Plate Tectonics, covering Lectures 4 & 5.
Learning Outcomes:
At the end of this lecture, students should be able to:
Describe the three different types of plate boundaries and the effects on the crust at each.
Sketch each type of boundary and provide examples.
Identify types of plate boundaries based on surface features.
List other geological processes occurring at different plate boundary types.
Explain the connection between plate tectonics and the occurrence of earthquakes and volcanoes.
Analyze how plate tectonics serves as a unifying theory in geology.
Types of Plate Boundaries
There are three key types of plate boundaries that define interaction characteristics.
Divergent Boundaries
Definition: Plates move apart, leading to the upwelling of material from the Mantle to create new sea floor.
Characteristics:
New oceanic crust formation
Rifting due to tensional stress
Earthquakes typical along these boundaries
Rift volcanoes may develop in weakened crust.
Formation: Hot material wells up, causing faulting and cracking as tension develops.
Example Locations:
Mid-Atlantic Ridge (oceanic-oceanic)
East African Rift (continent-continent)
Rifting Process:
Initial uplift and faulting lead to new ocean basins.
Example: The breakup of Pangea resulted from rifting processes.
Convergent Boundaries
Definition: Plates collide, resulting in one plate being subducted into the Mantle.
Categories:
Oceanic-Continental
Oceanic-Oceanic
Continental-Continental
Characteristics:
Compression leads to thrust faults.
Earthquakes and mountain building processes occur.
Depending on the type, subduction processes may result in volcanic activity or mountain formation.
Oceanic-Continental Collision:
Denser oceanic plate subducts beneath lighter continental plate, forming a trench.
Volcanic mountain belts develop as subducting plates melt and generate magma.
Example: Andes Mountains (Nazca Plate and South American Plate).
Oceanic-Oceanic Collision:
Older, denser plate subducts beneath the younger plate, creating volcanic island arcs.
Example: Mariana Islands (Mariana Trench).
Continental-Continental Collision:
Forms mountain ranges where two continental plates collide and crumple without subduction.
Example: Himalayas (India-Asia collision).
Transform Boundaries
Definition: Plates slide past each other, not creating or destroying lithosphere.
Characteristics:
Shearing forces cause earthquakes along strike-slip faults.
Links mid-ocean ridges to convergent boundaries.
Example: San Andreas Fault in California, with significant lateral movements.
Characteristics: Movement leads to various geological features but not the creation of new crust.
Earthquakes and Volcanoes at Plate Boundaries
How Earthquakes Occur at Plate Boundaries
Plates get stuck at edges due to friction, storing energy.
Strain builds until friction is overcome, resulting in a fault slip, which releases energy as seismic waves, causing ground shaking.
Locations of Earthquakes and Volcanoes
Correlation: Most earthquakes and volcanoes are located at plate boundaries, following specific patterns associated with the type of boundary.
Seismic Activity: Wadati-Benioff zone signifies increasing depth of earthquakes away from subduction zones.
Summary of Processes at Plate Boundaries
Earth Materials: Minerals and Rocks
Minerals: Definition, Properties, and Formation
What materials make up a landscape?
Observations about landscapes . . .
Yosemite cliff face appears as a homogeneous grey rock
Upon close examination, different colored grains within the rock become apparent: whitish, pinkish, clear gray, and black.
Further magnification reveals distinct minerals each with unique appearances.
Definition of a Mineral
A mineral is defined as:
Naturally occurring
Solid crystalline substance (with an ordered internal structure)
Inorganic
Specific chemical composition
Mineral Formation:
Formed through geologic processes (e.g., liquid magma cooling to solid minerals).
Importance: Minerals are the building blocks of rocks.
Example: Sodium Chloride (NaCl) - mineral consisting of salt.
Properties of a Mineral
Naturally Occurring:
Must be formed by natural processes.
Must be discovered in nature.
Ordered Internal Structure:
Comprises atoms arranged in an orderly manner.
Must be solid at normal Earth temperatures.
Inorganic:
Organic materials comprise both carbon (C) and hydrogen (H). Inorganic typically contains just one or the other.
Can be made by animals but still considered inorganic.
Defined Chemical Composition:
Specified by a chemical formula, indicating the major elements within the mineral.
Example: Pyrite = FeS\text{2}
These criteria allow for distinct physical properties that aid in identification (i.e., hardness, shape).
Differentiating Minerals and Rocks
Mineral:
Naturally occurring, inorganic, crystalline solid with a defined chemical composition.
Rock:
An aggregate or mixture of one or more minerals.
Key Concept: “Minerals are the building blocks of rocks.”
Example of Granite: Comprised of Quartz, Mica, and Feldspars.
Example of Quartzite: Dominated by quartz crystals.
Examples of Minerals
Minerals:
Pyrite:
Crystalline solid formed by geologic processes.
Kyanite:
Crystalline solid formed by geologic processes.
Non-Minerals:
Glass:
Not natural; made by humans.
Cubic Zirconia:
Composed in laboratories and not found in nature.
Importance of Minerals
Minerals are used daily; for example:
Brushing teeth with fluoride.
Consuming food like salt.
Cosmetic products and paints.
Components in everyday technology such as cellphones, cars, and bikes.
Common Minerals Used in Products:
Hematite, Magnetite, Copper sulfides, Quartz, Calcite, Halite, Apatite.
Why Study Minerals?
Understanding minerals assists in comprehending the geological history of rocks and identifying valuable resources.
Relationship Between Atoms, Minerals, and Rocks
Crust Composition:
Comprised of varied rock types.
Rocks consist of interlocking/bonded grains of material, typically minerals.
Composition of Minerals:
Minerals are constituted from elements.
Composition of Elements:
Elements are formed from atoms.
Atoms and Minerals
Structure of an Atom:
Composed of a nucleus surrounded by electrons.
Bonding:
Atoms bond together to form minerals, influencing properties based on types of atoms and bonds.
Chemical Bonds and Minerals
Bonds:
Chemical bonds are attractive forces holding two or more atoms together.
Electrons may be shared or transferred to create bonds, differing in strengths which affect mineral properties.
Types of Bonds:
Ionic Bonds:
Involves the exchange of outer electrons.
Example: Sodium loses one electron and chlorine acquires it forming NaCl.
Covalent Bonds:
Involves sharing electrons.
Physical Properties from Atomic Structure
Each mineral’s unique arrangement of specific atoms bonded in a repeating three-dimensional pattern (crystalline material) controls the crystal’s shape.
A chemical formula describes the ratio of different atoms present in each mineral.
Example: Halite:
Sodium (Na) surrounded by six chloride (Cl) ions.
Structure: Cubic.
Examples of Tetrahedra Arrangements:
Independent Tetrahedra.
Single Chains.
Double Chains.
Sheet Silicates.
Frameworks.
Concept Check Questions
Rank minerals, rocks, and atoms in terms of size: smallest to largest.
Is ice a mineral based on mineral requirements?
What significance do atomic bonds have in minerals? (Physical properties vs. just element presence)
Given a description of a physical object, identify if it's a rock or mineral based on visual characteristics.
How Do Minerals Form?
Atoms bond consistently in patterns during mineral formation.
Common Formation Methods:
As magma cools.
Through precipitation from water.
Under high pressure and temperature.
Formation from Magma:
Magma is liquid rock composed of different elements.
When it cools, atoms bond, creating new minerals (crystallization occurs).
Formation occurs at divergent plate boundaries, convergent plate boundaries with subduction, and hotspots.
Formation through Precipitation:
Minerals undissolve from water when ions are sufficiently concentrated, crystallizing and forming new minerals that accumulate at the bottom of the water body (common in sedimentary contexts).
Formation Under Pressure and Temperature:
Increased temperature and pressure can lead to the rearrangement of atoms into stable new bonds without melting, leading to the formation of new minerals influenced by preexisting ones (applicable to metamorphic rocks).
Rock-Forming Minerals and Groups
Rock-Forming Minerals
Most common elements in the Earth's crust by percentage:
Oxygen (O): 45.2
Silicon (Si): 27.2
Aluminum (Al): 8
Iron (Fe): 5.8
Calcium (Ca): 5.06
Magnesium (Mg): 2.77
Sodium (Na): 2.32
Potassium (K): 1.68
Other elements: 1.97
Mineral Groups
Minerals are classified into groups based on atomic composition:
Silicates: Contain O and Si; most abundant in crust.
Carbonates: Contain C and O.
Oxides: Contain O and metallic cations.
Sulfides: Contain S and metallic cations.
Sulfates: Contain SO\text{4} and metallic cations.
Silicate Minerals
Detailing silicon (Si) and oxygen (O) atoms strongly bound.
Two categories:
Felsic: Without iron (Fe) & magnesium (Mg).
Mafic: With iron (Fe) & magnesium (Mg).
Silicate Mineral Examples:
Mafic:
Hornblende: (Ca,Na)\text{2} (Mg,Fe,Al)\text{5} (Al,Si)\text{8}O\text{22} (OH)\text{2}
Olivine: (Mg,Fe)\text{2}SiO\text{4}
Pyroxene: (NaCa)(Mg,Fe,Al)(Al,Si)\text{2}O\text{6}
Felsic:
Quartz: SiO\text{2}
Muscovite Mica: KAl\text{2} (AlSi\text{3}O\text{10})(OH)\text{2}
Biotite Mica: K(Mg,Fe)\text{3} (AlSi\text{3}O\text{10})(OH)\text{2}
Potassium Feldspar: KAlSi\text{3}O\text{8}
Sodium Plagioclase: NaAlSi\text{3}O\text{8}
Carbonate Minerals
Contain carbon (C) and oxygen (O).
Examples:
Calcite: CaCO\text{3}
Dolomite: Ca(Mg)CO\text{3}
React to acids, releasing ions, water, and CO\text{2} gas.
Oxide Minerals
Ores of important metals, consisting of the oxygen (O\text{2} -) anion and metallic cations.
Examples:
Hematite: Fe\text{2}O\text{3}
Magnetite: Fe\text{3}O\text{4} (notably magnetic).
Sulfide Minerals
Ores of key metals.
Examples include:
Chalcopyrite: Cu-Fe-sulfide, major source of copper.
Pyrite: Fe\text{2}S, known as fool's gold.
Sulfate Minerals
Composed of a sulfate (SO\text{4} -2) anion and metallic cations.
Example:
Gypsum: Ca-Sulfate (SO\text{4} -2) + water, often formed through precipitation.
Concept Check Questions
Predict the appearance of gabbro, an igneous rock rich in iron (mafic) silicate minerals.
Classify minerals based on their chemical formulas as silicates or carbonates:
(Mg, Fe)\text{2}SiO\text{4}
NaAlSi\text{3}O\text{8}
Fe\text{2}S
Ca(Mg)CO\text{3}
Identifying Minerals: Diagnostic Properties
Identification relies heavily on observable physical properties, including:
Color
Hardness (indicates bond strength)
Cleavage (planar breaks along weak bonding)
Fracture (random breaks, no preferred plane)
Luster (reflective quality)
Streak (powder color)
Crystal shape (habit)
Transparency
Density (mass per volume), represented in g/cm³
Reaction to acid
Taste (in some cases)
Mineral Properties as Diagnostic Clues
Hardness and Density: Related to chemical bond strength.
Color: Helps infer mineral composition.
Reactivity to Acids: Indicates presence of certain materials.
Fracture Patterns: Reflect crystal structure, indicating distinctions like graphite versus diamond.
Assessment of Minerals
Color
Luster & Streak
Hematite’s streak.
Hardness:
Mohs Scale of Hardness
Talc (1) to Diamond (10)
Common examples on Mohs Scale:
Talc: Softest; scratched by fingernail.
Diamond: Hardest; resists scratching collectively.
Cleavage vs. Fracture
Cleavage:
Mineral breaks along flat surfaces due to weak bonding.
Fracture:
Random breakage without defined planes.
Common Cleavage Types
One Direction of Cleavage:
Example: Micas
Two Directions of Cleavage at 90°:
Example: Feldspars
Three Directions of Cleavage, Not at 90°:
Example: Calcite
Three Directions of Cleavage at 90°:
Example: Halite, Galena
Cleavage Development
Cleavage is determined by the orderly atomic arrangement that affects crystal shapes and how crystals break.
Breaking requires overcoming bonded forces, where minerals tend to cleave preferentially along the weakest links.
Chemical Structure & Cleavage in Silicates
Classified by linkage patterns:
Isolated Tetrahedra
Single-Chain Linkages
Double-Chain Linkages
Sheet Linkages
Framework Structures
Crystal Habit (Shape)
Describes ideal shapes of crystal faces, influenced by environmental growth conditions.
Common terms include:
Cubes, Octahedra, Blades, Hexagonal Prisms, Dodecahedra.
Reaction to Acid - Identification Method
Certain minerals react to acid indicating presence of particular compounds.
Example:
Reaction of calcite (CaCO\text{3}) with hydrochloric acid (HCl) resulting in CO\text{2} and H\text{2}O.
Rocks: Definition, Classification, and Cycle
Definition of Rocks
Definition: Rocks are naturally occurring aggregates of minerals.
Characteristics to consider:
Composition
Texture
Rock Texture
Types of textures:
Crystalline: Composed of interlocking minerals that grew together under high-temperature conditions.
Forms by crystallization of magma, metamorphism, or precipitation from hot water.
Clastic: Composed of pieces derived from older, weathered, and eroded rocks.
Commonly formed in low-temperature environments like sand dunes, rivers, and beaches.
How to Describe Rocks
Attributes to classify a rock:
Type of minerals
Sizes of crystals or clasts
Shapes of crystals or clasts
Presence of layers or lack thereof
Rock Classification
Three main types of rocks based on formation:
Igneous Rocks
Sedimentary Rocks
Metamorphic Rocks
Importance of understanding formation processes and unique characteristics of each type.
The Rock Formation Process
Igneous Rocks
Form from the cooling and solidification of magma.
Types of Igneous Rocks:
Extrusive: Form when molten material cools quickly at the Earth's surface.
Intrusive: Form when molten material cools slowly below the Earth's surface.
Texture: Influenced by the cooling rate; rapid cooling yields fine-grained rocks while slow cooling results in coarse-grained rocks.
Sedimentary Rocks
Form from sediments that settle through air or water, resulting from:
Weathering and erosion of existing rocks.
Two sedimentary types:
Clastic Sedimentary Rocks: Composed of fragments of rock.
Chemical Sedimentary Rocks: Form from mineral precipitation from solution.
Biogenic Sedimentary Rocks: Form from biological material (e.g., skeletons of organisms).
Processes include:
Lithification: The process of compacting and cementing sediments together into solid rock. This involves:
Compaction: Reduction of space between particles due to pressure.
Cementation: Binding of sediment grains through mineral precipitation from groundwater.
Metamorphic Rocks
Form through alteration of existing rocks due to high pressure and temperature conditions without melting.
Processes that lead to metamorphic rock formation:
Burial and deep burial: Associated with mountain building.
Contact metamorphism: Occurs due to proximity to nearby magma.
Hydrothermal fluids: Hot fluids that impact rock structure.
Changes include solid-state chemical reactions and recrystallization.
Rock Cycle Model
Concept: Rocks continually change form through various geological processes identified in the rock cycle.
Rocks can transition between the three types based on environmental conditions such as temperature, pressure, and melting:
Igneous can erode into sediments, transforming into sedimentary rocks.
Sedimentary rocks can undergo metamorphism to become metamorphic rocks.
Illustrated by examples:
Sand dunes lead to lithified sandstone.
Metamorphosed limestone creates marble.
Connections to Plate Tectonics
Rock types display specific distributions according to tectonic settings:
Divergent Boundaries: Formation of igneous rocks as plates separate.
Convergent Boundaries: Can create sedimentary and metamorphic rocks depending on subduction.
Features of passive margins lead to sedimentary rock formation by sediment deposition in shallow waters.
Hotspots: Sites of volcanic activity leading to the formation of igneous rocks.
Concept Discussions
Challenges in understanding the rock cycle:
Debate 1: Validity of rock type transitions and formations.
Clarification on sequence of rock formation processes: Weathering, Erosion, Deposition, Lithification.
Geological maps: Provide insights into rock types found at Earth’s surface for various stakeholders including geologists, engineers, and city planners.
Key information can include rock age and composition, as indicated by colors on the map.
Example Map Details:
Sedimentary Rocks (Cenozoic, Mesozoic): Descriptions include various layers of sand, clay, and limestone.
Igneous and Metamorphic Rocks: Specific formations such as basalt and granite are noted.
Igneous Rocks: Formation, Types, and Magma Processes
Overview of Igneous Rocks
Formation:
Igneous rocks originate from liquid rock (magma).
Intrusive igneous rocks form from magma that cools within the Earth.
Extrusive igneous rocks result from lava that cools at or near the Earth’s surface.
Differences Among Igneous Rocks
Texture and Composition
Texture refers to crystal size:
Coarse-grained rocks (large crystals)
Fine-grained rocks (small crystals)
Mixed texture rocks (a combination of large and small crystals)
Texture correlates with cooling rate:
Intrusive igneous rocks cool slowly, leading to larger crystals.
Extrusive igneous rocks cool rapidly, resulting in smaller crystals.
Varieties of textures include fine-grained, glassy, and vesicular textures.
Mineral Size and Location of Cooling
Cooling Locations:
Fine-grained (texture = aphanitic):
Characteristics: Small minerals, visible only under a microscope
Type: Extrusive
Coarse-grained (texture = phaneritic):
Characteristics: Large minerals, visible to the naked eye
Type: Intrusive
Glassy: No minerals formed due to rapid cooling, thus appearing glass-like.
Type: Extrusive
Porphyritic: Exhibits two different mineral sizes, resulting from two stages of cooling (first underground, then at the surface).
Cooling Times for Various Types
Ash: Cooling time = minutes
Lava Flow: Cooling time = days to months
Deep Plutons: Cooling time = centuries to a million years
Shallow Sills: Cooling time = weeks to months
Coarse-Grained Granite: Medium cooling and slow heat escape
Glassy Obsidian: Very fast cooling
Porphyritic Rocks: Slow first, then fast cooling
Classification of Igneous Rocks
Based on Composition and Texture
Silica Content: Determines the classification of igneous rocks into various categories:
High Silica: Felsic
Medium Silica: Intermediate
Low Silica: Mafic
Color Proxy: Color can indicate silica content:
Dark = low silica (Mafic)
Light = high silica (Felsic)
Specific Rock Examples
Felsic: Granitic rocks such as:
Rhyolite (extrusive)
Granite (intrusive)
Intermediate: Diorite (intrusive) and Andesite (extrusive)
Mafic: Basalt (extrusive) and Gabbro (intrusive)
Ultramafic: Peridotite (intrusive)
Identifying Igneous Rocks
Use texture and composition to classify igneous rocks:
Composition indicates which minerals are present (indicated by color).
Texture indicates the size of the minerals present.
Mineral Formation from Magma
As magma cools, minerals form at different temperatures:
Early crystallizing high-temperature minerals will solidify first and lower-temperature minerals will remain molten longer.
Bowen’s Reaction Series: Describes the sequential order of mineral crystallization in cooling magma:
Higher temperature minerals crystallize first while lower temperature minerals crystallize later.
Relevance of Partial Melting: Initially heavy, mafic minerals crystallize, transforming the remaining magma composition, leading to different rock types over time.
Mechanisms Leading to Melting
Increase in Temperature: Necessary to rise above the melting point of the rock, affected by both composition and pressure conditions. However, this is not the primary way most magma forms.
Partial Melting Mechanics: Rock components melt at varying temperatures. As certain minerals melt (melt first), the remaining solid alters the chemical composition of the magma.
Decrease in Pressure: Decompression melting, prevalent at divergent boundaries where solid mantle rock rises and melts due to falling pressure as tectonic plates separate.
The resultant magma is typically mafic in composition, forming basalts and gabbros.
Adding Water: Reduces the melting temperature of rock, facilitating melting even without pressure change and is notably significant in sedimentary rock environments during subduction zones.
Subduction Zone Melting Processes
Fluid-induced Melting: Water released from subducting plates into the hot mantle lowers the melting point, generating silicic (felsic) to mafic magmas.
Composition evolves depending on the material present and how it interacts in the crust.
Summary of Melting Processes
There are three primary ways for rocks to melt:
Increase Temperature: Partial melting near magma chambers.
Decrease Pressure: Critical in rifting zones and beneath hotspots.
Add Water: Facilitates fluid-induced melting primarily at convergent boundaries.
Volcanism
Introduction to Volcanoes
Volcano: A hill or mountain created from the accumulation of erupted lava and pyroclasts around a central vent.
Why Do Volcanoes Erupt?
Magma and Gas Importance:
Magma contains dissolved gases including H\text{2}O, CO\text{2}, and SO\text{2}, which significantly influence eruption styles.
High confining pressure keeps gases dissolved deep underground. As magma rises, pressure drops, allowing gas bubbles to form (similar to opening a soda bottle).
If bubbles form rapidly, they enhance magma buoyancy, causing it to rise more easily and potentially erupt.
Volcanic Eruptive Products and Lava Types
Volcanic Eruptive Products
Besides lava flows, volcanoes emit various products:
Pyroclasts: Fragments formed from magma shattering due to rapid gas release. Example includes cinders, which are gravel-sized basalt pieces.
Bombs: Large lava fragments ejected during eruptions; these can cool into rounded shapes.
Volcanic Ash: Tiny pulverized rock and minerals (less than 2 mm in diameter) that can cause significant hazards, such as the threat to aircraft engines demonstrated during the Eyjafjallajökull eruption in 2010.
Pyroclastic Deposits
When pyroclasts settle back to Earth, they create large deposits, which solidify over time. Key types are:
Welded Tuff: Formed from compacted volcanic ash.
Volcanic Breccia: Composed of fragmented minerals or rocks cemented together.
Types of Lava
Three main lava types produce unique landforms:
**Basaltic Lava (1000-1200°C):
Composition: 45-55\text{SiO}\text{2} (high in Fe, Mg, Ca; low in K, Na)
Characteristics: Low viscosity, flows readily.
**Andesitic Lava (800-1000°C):
Composition: 55-65\text{SiO}\text{2} (medium amounts of Fe, Mg, Ca, K, Na)
Characteristics: Intermediate viscosity and gas content; explosive potential.
**Rhyolitic Lava (600-800°C):
Composition: 65-75\text{SiO}\text{2} (low in Fe, Mg, Ca; high in K, Na)
Characteristics: High viscosity leads to explosive eruptions.
Importance of Magma Composition in Eruptions
Differences Between Magma Types:
Felsic Magma:
High viscosity due to silica content.
Higher volatile content leads to more explosive eruptions.
Mafic Magma:
Low viscosity allows for gentle eruptions as gases can easily escape.
Eruption Mechanics:
Basaltic lava flows easily, while rhyolitic lava is sticky, leading to potential explosive activity when pressure builds.
Characteristics of Lava Flows
Basaltic Flow: Fluid and can travel long distances, forming thin sheets.
Andesitic Flow: More viscous and breaks as it flows.
Rhyolitic Lava: Very viscous; tends to form thick, bulbous deposits at the vent.
Summary of Magma Viscosity and Eruptions
Basaltic lava erupts gently, allowing gases to escape, whereas rhyolitic lava can cause explosive eruptions due to gas buildup.
Concept Questions
What role does gas play in eruptions?
Compare and contrast cinders, bombs, and ash.
Define the viscosity differences among lava types and their eruption styles.
How does the composition of lava influence the resultant rock type?
Identify which type of lava is associated with high viscosity and which is fluid-like.
Types of Volcanoes and Intrusions
Volcano Types
Volcano classification is based on erupted materials and form:
Types:
Shield Volcano: Broad, gently sloping sides with mainly basaltic lava, characterized by peaceful eruptions.
Cinder Cone: Built from pyroclastic fragments, tends to be small with explosive spitting eruptions.
Stratovolcano (Composite Volcano): Steep-sided, formed from alternating layers of lava flows and pyroclasts, typically associated with explosive eruptions above subduction zones.
Volcanic Dome: Mound-like feature composed of high-viscosity lava, can cause explosive eruptions when they trap gas.
Caldera: A large basin formed after a violent eruption empties the magma chamber, leading to the collapse of the overlying rock.
Volcanoes and Igneous Rock Formations (Plutons)
Plutons:
Large igneous intrusions that cut across existing rock layers.
Formed from more viscous magma (intermediate to felsic).
Forms of Igneous Intrusions
Sills:
Sheet-like bodies injected between bedded rock layers; can vary in thickness and can extend over large areas.
Dikes:
Magma intrusions that cut across layered rock; important for magma transport within the crust.
Flood Basalts
Large, flat lava flows from fissures instead of central vents, creating vast regions of basaltic rock.
Plate Tectonics and Volcanism
Volcano Formation:
Occurs at rifts, subduction zones, and hot spots.
Types of volcanoes:
Island Arc Volcanoes: All active, formed from subduction.
Hotspot Volcanoes: Active at one site above mantle plume, e.g., Hawaiian Islands.
Different tectonic settings lead to various magma compositions and resultant volcanic activity:
Divergent Boundaries: Primarily form basaltic lava while creating new oceanic crust.
Convergent Boundaries: Subduction leads to intermediate and felsic lava, often producing stratovolcanoes.
Hotspots: Can result in both mafic and felsic lavas, leading to different eruption styles depending on magma composition.
Summary of Plate Tectonics and Volcano Types
At ocean-ocean convergences, basaltic lavas dominate, while ocean-continent convergences yield a mix of magmas leading to andesitic volcanism.
Hotspots may produce varied volcanic forms depending on underlying crust.
Volcanic Hazards and Monitoring
Volcanic Hazards
Primary Hazards: Determined by the eruptive materials, which depend on the magma composition.
Types of Hazards:
Lava
Pyroclastic flows
Ash
Gas
Lahars
Landslides
Volcanic Hazards: Lava
Definition of Lava: Magma that has breached the surface.
Types of Lava Flows:
Mafic lava flows: More common than felsic flows due to lower viscosity and dissolved gas content.
Felsic flows: More explosive than flowing due to higher viscosity.
Hazards of Lava:
Generally flows at a speed allowing humans to evacuate.
Extremely hot: temperatures can reach 1200°C or 2200°F.
Can bury and destroy infrastructure such as roads.
Example: La Palma - Canary Islands
Lava from the volcano destroyed hundreds of homes while advancing towards the ocean.
Geological Setting: Canary Islands Hot Spot.
Path of Lava Flow: Illustrated in geographic mapping sources (Copernicus EMS Rapid Mapping, 29 Sep).
Impact Details: Events summarized through local reporting (BBC).
Volcanic Hazards: Pyroclastic Flows
Definition: A glowing cloud of extremely hot ash, dust, and gases emitted during volcanic eruptions.
Mechanism:
Occurs when an eruption column collapses due to density and flows downhill.
Travel speeds >100 km/h.
Effects of Pyroclastic Flows:
Destroys or buries objects and structures in its path.
Can impact areas up to 5 – 20 km from the summit, especially in larger eruptions.
Common Locations: Often found at stratovolcanoes due to their magma composition (intermediate to felsic).
Case Studies of Pyroclastic Flows
Mount Pinatubo, Philippines: Eruption initiated pyroclastic flow development.
Mount Unzen, Japan: Demonstrated pyroclastic activity and hazards in eruptions.
Volcanic Hazards: Ash
Nature of Ash: Smallest particles resulting from pyroclastic activity, capable of being transported over vast distances (thousands of miles).
Hazards Associated with Ash:
Airborne ash can disable aircraft engines.
Collapsing buildings due to accumulated ash weight.
Climate impact through solar obstruction leading to cooling.
Agricultural destruction, respiratory problems, and disruption of daily life.
Possible at any type of volcano.
Ashfall in History
Example: Significant ashfall observed at Mount St. Helens post-1980 eruption, demonstrating the environment's impact on surroundings.
Volcanic Hazards: Gas Emissions
Primary Gas Components:
Mainly water vapor, carbon dioxide, sulfur dioxide, hydrogen sulfide, and hydrogen halides.
Emission During Eruptions: Large volumes, particularly during major eruptions or high-volume flows often associated with stratovolcanoes.
Environmental Effects:
Long-range effects: Climate cooling (1° to 2°C for months/years) leading to potential crop failure and famine.
Local dangers include poisoning effects to inhabitants and wildlife.
Case Example: Kilauea 2014 - health alerts for individuals with respiratory ailments due to volcanic fumes.
Volcanic Hazards: Lahars
Definition: Mixtures of water, rock, sand, and mud rushing down valleys away from a volcano.
Formation Triggers: Caused by melting snow and ice or rain mixing with loose ash.
Travel Characteristics and Risks:
Can travel speeds of >50 miles per hour over distances exceeding 50 miles.
Appearance akin to fast-moving concrete rivers, posing serious risks to life and infrastructure.
Volcanic Hazards: Landslides
Definition: Collapse of the volcanic structure triggered by earthquakes or inherent instability in volcanic rock.
Prominent Cases:
Mount St. Helens' landslide before the 1980 eruption.
Mount Meager (British Columbia, Canada) experienced a landslide of 45,000,000\text{m}\text{3} of debris in 2010 due to unstable slopes.
Evaluating Volcano Danger
Assessment Factors:
Volcanic type inferred from shape and rock types, along with volcanic history.
Proximity of communities to the volcano affects risk levels; topography (valley vs. ridge) also plays a significant role.
Wind patterns influence ash and gas distribution, affecting communities downwind.
Case Study: Mount Rainier
Positioned within a chain of volcanoes over the Cascadia subduction zone.
Assessment of interrelated hazards based on geological maps considering the volcanic type and structure.
Risk evaluation for surrounding towns and structures within the Puyallup and Nisqually River valleys.
Volcanic Hazards Summary
Recognizing that volcanic hazards are natural disasters leading to fatalities and indirect consequences (e.g., famine).
Hazard types include landslides, lahars, pyroclastic flows, and gas emissions, marking various levels of risk to human life and infrastructure.
Summary Chart: Volcanic Hazards
Lava Flow: Description: Slow-moving from the vent; Risk: Moderate due to potential escape opportunities.
Pyroclastic Flow: Rapid and extremely hot; Extreme hazard — destruction imminent in vicinity.
Ash: Damaging to health and infrastructure; Risks include respiratory issues, aircraft hazards, and agricultural impact.
Gas Emissions: Potentially poisoning; Severe risks from climate effects and immediate health hazards.
Lahars: Triggered by snow/ice or heavy rain; Severe risk along flow paths.
Landslides: Dangerous, especially along stratovolcano structures post-eruption or trigger events like earthquakes.
Activity Discussion
Student discussions on the dangers of various eruptions concluded on pyroclastic flows being the deadliest due to suffocation and destruction in the path.
Evaluative group activity discussing the types of volcanoes and hazards represented by geographic settings & risk profiles.
Monitoring Volcanoes and Predicting Eruptions
Interpreting Past Volcanic Eruptions
Methods for Timing Eruptions:
Radiocarbon dating on buried flora.
Utilizing historical records for more recent events.
Radiometric techniques on ancient volcanic structures.
Eruptive Style Determination: Past deposits indicative of recurring hazards (e.g., mapping pyroclastic flow deposits).
Future Predictability Through Monitoring: Continuous observation for eruptive patterns aligns well with recent activity leading to recognition of hazard trends.
Monitoring Techniques
Seismicity:
Volcanic earthquakes signify magma movement, detectable by seismometers.
Gas Emissions: Changes in gas output are key predictive markers for eruptions (CO\text{2} and SO\text{2} emissions).
Ground Deformation: Measured by GPS and tiltmeter systems indicate magma chamber pressures and impending eruptions.
Signs of Imminent Volcanic Activity (USGS)
Gas Leaks: Increased emission of volcanic gases through surface cracks.
Bulging Formation: Evidence of magma swelling, indicated by surface changes.
Seismic Activity: A sharp increase in the number of small earthquakes suggests magma movement.
Rapid Seismic Decline: Potentially indicates magma stall, foreshadowing eruption.
Surface Distortions: Pronounced bulges suggest magma proximity to the surface.
Steam Eruptions: Occurs from groundwater superheating leading to explosive ejection of materials.
USGS Alert Levels
Facilitation of Public Safety: A structured alert system to categorize and communicate potential volcanic activity to mitigate risks.
Concept Questions
Discussion on geological evidence of eruptions: deposits vs. eyewitness accounts.
Integration of monitoring techniques and trends in eruption predictability in discussion.
Identification of crucial instruments in volcanic studies and monitoring.
Case Study 1: Mount St. Helens, Washington
Geological Context: Formed by the subduction of the Juan de Fuca plate beneath North America, characterized as a stratovolcano with intermediate magma characteristics.
1980 Eruption Details: Magma emplacement led to significant geological activities including the formation of a bulge indicative of imminent eruption.
Eruption Events of 1980
Event Timeline:
Incremental magma intrusions and shallow earthquakes indicated unrest.
Steam and ash eruptions gained frequency leading up to May 18.
The significant bulge on the north flank increased in size rapidly—140 m by May 17.
Explosion Sequence:
8:32 AM magnitude 5.1 earthquake triggers a landslide, unleashing explosive pressure from magma beneath the surface.
Resulted in one of the largest debris avalanches recorded, extensive pyroclastic flows, and large ash clouds.
Case Study 2: Mount Vesuvius & Pompeii
Geological Characteristics: Stratovolcano over a subduction zone with andesitic magma leading to explosive eruptive behavior.
79 A.D. Eruption Impact: Catastrophic ash, mud, and rock flows buried Pompeii and Herculaneum, historically documented.
Eruption Accounts: Explosive characteristics described using comparisons to natural forms (e.g., pine trees).