What is geology, and what is the difference between physical and historical geology?
Geology is the scientific study of the Earth and its major systems
Physical Geology is the Study of the Earth's composition. structure, and the processing that shape it
Historical Geology is the Study of Earth's history and the history of life
With respect to why we study geology, in class I cited three areas of benefit to humanity where geologic knowledge is needed. What are these three?
Obtain Natural resources
Assess and avoid natural hazards
Prevent or correct environmental damage
In what way does geology expand our awareness of the Earth?
How beautiful and complex the Earth is
How our survival depends on understanding the Earth
What are the details of the scientific method, and what is the difference between a hypothesis, and a theory?
What is the Scientific Method
A systematic, logical way of studying how nature works
Hypothesis is a question theory proves a hypothesis
What is the atmosphere, and what are its two most abundant gases?
Gaseous envelope surrounding Earth.
(Air we breath)
What is the hydrosphere, what are its various components, and which of these contains the majority of its substance?
All of Earth's water 97% is in oceans
What is the geosphere, and what are the characteristics of the following subdivisions: Crust (Continental and Oceanic), Mantle, Outer Core and Inner Core.
Geosphere is earth’s Surface to its center
Thicker, variable thickness, and granitic average composition.
Thinner, more uniform in thickness, and basaltic composition
Most of Earth's volume and mass. Denser rock than crust
Molten outer core, and solid inner core. Iron and nickel composition.
What is the biosphere?
All life on Earth
What does it mean when we say that the atmosphere, geosphere, hydrosphere, and biosphere are in a state of dynamic equilibrium with respect to one another? (consult your notes for the definition. This concept is discussed in the book under the heading of "Earth as a System").
What is the difference between continental and oceanic crust as far as their thickness, composition, height relative to sea level, and relative amount of the Earth’s surface is concerned?
Thicker, variable thickness, and granitic average composition.
Thinner, more uniform in thickness, and basaltic composition
What is the nature of such physiographic features as: continental shelves, continental slopes, oceanic ridges, deep-ocean trenches, and volcanic island arcs?
Undersea mountain range extending through all the oceans
Deep Trenches Ocean
Trough-like depressions that are the deepest parts of the oceans.
Volcanic Island Arcs
Curving chains of volcanic islands that are next to a trench
What is geologic time and why does it enable us to use ordinary, observable processes to explain most of what we see on earth (uniformitarianism).
Vast spans of time ranging from thousands to billions of years
Uniformitarism? requires long periods of time for most changes to occur and thus required an old Earth; the physical, chemical, and biologic laws that operate today have operated throughout the geologic past.
What is the basic premise of the rock cycle?
What are igneous, sedimentary and metamorphic rocks, and what processes are needed to transform rocks from each of these types into rocks of the other two types?
Melted rock cools and solidifies
Rocks weather and erode into sediment that becomes new rocks
Rocks recrystallize without melting, due to heat and pressure deep underground
What is the basic premise of the hydrologic cycle, what are its components, and what powers it? (see chapter 11 for a discussion of this topic)
Continuous transfer of water from one repository to another
What is the theory of plate tectonics?
Plate tectonics is the theory that the outer rigid layer of the earth (the lithosphere) is divided into a couple of dozen "plates" that move around across the earth's surface relative to each other, like slabs of ice on a lake.
What are the lithosphere and asthenosphere, and how do they relate to plate tectonics?
On the Earth, the lithosphere includes the crust and the uppermost mantle which is joined to the crust across the mantle. The lithosphere is underlain by the asthenosphere, the weaker, hotter, and deeper part of the upper mantle. The boundary between the lithosphere and the underlying asthenosphere is defined by a difference in response to stress: the lithosphere remains rigid for long periods of geologic time, whereas the asthenosphere flows much more readily. As the conductively cooling surface layer of the Earth's convection system, the lithosphere thickens over time. It is fragmented into tectonic plates which move independently relative to one another. This movement of lithospheric plates is described as plate tectonics. This is when plates move horizontally across the Earth's surface and the continents change their relative positions.
If the core cooled enough for the mantle to solidify, the tectonic plates would stop moving because they move on the semi-liquid mantle.
What is the difference between divergent, convergent and transform plate boundaries, and what types of processes and features are associated with each?
Two plates move away from one another
Two plates collide, one goes under, one into mantle and gets recycled
Two plates slide past one another
Chapter 2: Minerals: Building Blocks of Rocks
What is a rock, and what is a mineral? rocks Consolidated mineral aggregates
minerals what rocks are made of
What is an element, which are the two most abundant elements in the Earth’s crust? element Substances that can't be chemically broken down into other substances.
Oxygen and Silicon are the most abundant
What is a crystalline solid, and how do crystals form and grow? how do crystals form and grow?
By accretion, i.e. adding more atoms to their outer surface.
What is crystal form, what happens to it as long as a crystal's growth is not interfered with?
What is crystal form
Crystals that have a geometric face.
what happens to crystal form as long as a crystal's growth is not interfered with?
Retain their shape.
What is a crystalline aggregate?
The result of crystals merging together.
What are physical properties of minerals, and what is the definition of the following examples: cleavage, fracture, hardness, color, streak, luster, and specific gravity (density)?
Breaks along flat planes in a preferred direction or directions.
Doesn't break along flat planes. Breaks like glass, rock, or wood.
Resistance to wear (how easily it can be scratched).
The wavelength of light reflected.
Color when powdered on unglazed porcelain tile (streak plate).
How it reflects light.
specific gravity (density)
Mass/Volume, i.e. weight compared to size.
What causes some minerals to exhibit cleavage whereas others do not?
Some atomic bonds are weaker.
You should be familiar with the following mineral groups, and know examples of each: silicates, carbonates, sulfates, halides, native elements, oxides, and sulfides.
Made of at least silicon and oxygen, and usually other elements as well, typically the other most abundant ones. 92% of crust by volume.
Example of Silicates
Quartz, Muscovite Mica, Clay Minerals, Talc.
Minerals containing CO3-2 (carbonate ion)
Examples of Cabonates
Minerals containing SO4-2 (Sulfate ion)
Examples of Sulfates
An alkali metal plus a halogen gas
Examples of Halides
Halite (Rock Salt)
Minerals made of a single element
Examples of native elements
Gold, Silver, Platinum, Copper, Sulfur, Carbon (diamond and graphite)
Oxides appropriate element plus oxygen.
Examples of oxides
Water Ice, Hematite, Magnetite, Bauxite
Any appropriate element plus sulfur. Most important group of ore minerals.
Examples of sulfides
Pyrite (fool's gold), Galena (lead ore), Sphalerite (zinc ore)
You should know which of these are noted as important rock-forming mineral groups, and which are known primarily as nonrock-forming mineral groups.
Nonrock-forming mineral groups
Native elements, Oxides, Sulfides
Rock-forming mineral groups
Carbonates, Sulfates, Halides, Silicates
Which of these groups is the most abundant group of minerals in the Earth’s crust?
What is the difference between ferromagnesian and nonferromagnesian silicates?
Contain iron and/or magnesium. Typically dark and relatively heavy
Non ferromagnesian silicates
Don't contain iron or magnesium. Typically light colored and less dense
Concerning the silicates, the following minerals are important: ferromagnesian silicates, muscovite mica, clay minerals, quartz, and feldspars.
Examples for non ferromagnesian silicates quartz, mica, different kinds of feldspar.
Aluminum silicates with calcium, sodium or potassium . Most abundant of the silicates (51% of the crust)
What are geologic resources, and what is the nature of the following examples: ore minerals, industrial minerals, building stone, and fossil fuels? geologic resources
Any mineral, rock, or other geologic material that is useful and profitable to extract.
You should know which of the previously mentioned mineral groups contain many ore minerals, and which group contains more than any other, as well as the specific examples of ore minerals from these groups that were given in class.
Oxides, sulfides, and native elements
Chapter 3: Igneous Rocks
What is magma, from where does it come, and of what does it consist?
What is magma?
Where does magma come from? lower crust and upper mantle
What does magma consist of
Feldspars, Quartz, Mica, Ferromagnesians
What are the two most abundant gases dissolved in magma? water vapor and sulfur dioxide, carbon dioxide
What is the geothermal gradient, and how does it relate to the generation of magma?
Rate of temp rise as depth increases. Very important to magma formation. Magma is most likely to form where the gradient is high.
Why does magma move upward toward the Earth’s surface, and what are the four processes by which it accomplishes this? (consult your notes for this last part)
Once formed, magma tends to rise because it is less dense than solid rock. It does this by: Pushing, Melting, Quarrying, Moving through open fractures or vents (fastest).
Magma intrudes cracks wedging out rocks that sink into it.
When does magma become lava, and what part of magma is lost when this happens?
Magma becomes lava after reaching a volcano's vent
Lava is magma that has lost its gases
What are igneous rocks, how do they form, and what is the difference between plutonic (intrusive) and volcanic (extrusive) origin?
Igneious Rocks are crystalline or glassy rocks formed when molten rock (magma/lava) cools and solidifies
Plutonic: Formed underground (also called intrusive)
Volcanic: Formed on the surface (also called extrusive)
What are the different types of igneous rock textures, and how do they relate to the cooling rate of the magma which formed the rock and where the cooling took place (the rock’s origin - i.e. volcanic or plutonic)?
Volcanic Textures and Plutonic Textures
Volcanic = fast cooling = fine grained or glassy textures
Plutonic = slow cooling = visible crystals.
What is the difference between rocks of felsic (granitic), intermediate (andesitic), and mafic (basaltic) composition?
Felsic: Mostly light colored minerals - potassium feldspar, sodium feldspar and quartz with a small % of ferromagnesians.
Intermediate: Nearly equal amounts of light (intermediate feldspar) and dark (ferromagnesian) minerals.
Mafic: Mostly or entirely dark minerals - calcium feldspar, and ferromagnesians (45-85%).
What is the composition, origin, and texture of the following rocks: granite, rhyolite, diorite, andesite, gabbro, and basalt?
Felsic (mostly light colored minerals)
Typically pink or white with small % of dark minerals.
Most common continental plutonic rock.
Intermediate (medium dark)
Roughly = mix of gray and/or white and black
2nd most common plutonic rock.
Dark gray, greenish gray, or black.
Least common continental plutonic rock, but common in oceanic crust.
Felsic. Fine-grained crystalline. Pink, purple, or light gray. Least common lava.
Intermediate. Fine-grained crystalline. Medium gray. Common lava in volcanic island arcs and continental volcanic arcs.
Mafic. Fine-grained crystalline. Dark gray to black. Often has gas bubbles. Most common lava. Upper ocean crust is basalt.
What are pyroclastic igneous rocks, and what is tuff formed from?
What are pyroclastic igneous rocks?
Made of explosively ejected particles that are compressed and cemented, or welded.
What is tuff formed from?
Pyroclastic rock made of tiny ash particles that have been compressed and cemented or heat welded.
How are glassy igneous rocks different from the rest of the igneous rocks, and how do obsidian and pumice differ from one another?
Made of volcanic glass. Cooled too fast to form crystals.
Obsidian: Is sometimes translucent or even clear (no impurities).
Pumice: Very light weight, often floats in water.
What are plutons, and what is meant by concordant and discordant, and tabular and massive (nontabular) plutons?
What are plutons?
A mass of igneous rock formed underground
What is meant by concordant?
Matches up with structure of surrounding rocks
What is meant by discordant?
Cuts across rock structure
What is meant by tabular?
What is meant by massive (nontabular) plutons?
Any shape besides tabular. Often bulbous or lens-shaped.
What are dikes, sills, laccoliths, stocks, and batholiths, how do they form, and which of them is the largest?
They are all intrusive igneous rocks
What are dikes?
Vertical or Steeply inclined
Forms when magma intrudes into cracks
Forms a wall like mass if it is more resistant than surrounding rock.
Associated with fissure eruptions.
What are sills?
Forms when magma intrudes between layers
What are laccoliths?
Forms when magma pushes up rocks more in the center than the edges.
What are batholiths? biggest
>100 km2 (40 mi2) of exposed rock
Made of granite and/or diorite
Batholiths can cover 10s of 1000s of Km
What do stocks and batholiths have in common, how are they different, of what sort of rock are they typically made, and how do they usually form?
Describe each of the four intrusive igneous features discussed in the text (dike, sill, laccolith, and batholith).
Formed by magma
Batholiths = "big" plutons; or large bodies made up of smaller plutons
Stocks = "small" plutons
Sills = Concordant intrusions
(Layers of frosting between 2 layers of cake/Parallel to layer above & below)
Dikes = Discordant intrusions
• Vertical between Volcano
Chapter 4: Volcanoes and Other Igneous Activity
What is the difference between explosive and effusive (quiescent) volcanic activity?
The subduction of oceanic crust under continental crust predominantly produces which kind of volcanic eruption? High viscosity and dissolved gas
Violent and explosive
The subduction of oceanic crust under oceanic crust is likely to produce which type of eruption?
Quiet and effusive
What is magma viscosity, and what effect does silica have on it?
Magma Viscosity- how easily it flows
Higher silicia= higher viscosity
How does the composition and temperature of magma/lava affect its viscosity?
High viscosity= doesn't flows easy (thick)
Low viscosity= fluid (flows easily)
Viscosity and gases
H.V-Difficult for gases to escape, and pressure builds to explosive levels.
L.V-Gases easily escapes , creating effusive eruptions.
Felsic to intermediate form at shallow depths, thus are cooler ,more viscous.
Mafic forms deepest, thus hotter, more fluid.
What happens to dissolved gases in magma as it nears the surface, and what is the most abundant gas released in volcanic eruptions? gases expand within a magma as it nears the Earth's surface due to decreasing pressure, the violence of an eruption is related to how easily gases escape from magma water vapor is the most abundant gas released
How do viscosity and magma gases relate to whether a volcanic eruption is explosive or effusive?
________ tend to increase the explosive potential of a magma body beneath a volcano.
High viscosity and dissolved gas
What is the nature of the following typical volcanic features: volcanic cone, vent, crater, caldera, and fissure?
What is the nature of summit, flank, vent and fissure eruptions?
What type of eruptive behavior is typical of volcanoes that erupt mafic (basaltic) low silica lava?
Concerning the following mafic volcanic structures, you should know the basic characteristics, and how they are formed: cinder cones, shield volcanoes, and flood lava plateaus.
Cinder Cone a small volcano built primarily of pyroclastic material ejected from a single vent
Shield Volcano a board, gently sloping volcano built from fluid basaltic lavas
TYPES OF Volcanoes
Shield volcano(LARGEST), Composite Cone/Stratovolcano (medium-sized), Cinder Cone (smallest).
Concerning the following types of mafic lava flows, you should know the basic characteristics, and how they are formed: pahoehoe, aa, and pillow lava.
What type of eruptive behavior is typical of volcanoes that erupt intermediate to felsic high silica lava, and how do the relative amounts of pyroclastic material and lava erupted compare with that of mafic eruptions?
Concerning the following intermediate to felsic volcanic structures you should know the basic characteristics, and how they are formed: composite cones (stratovolcanoes), collapse calderas, and lava domes.
What are the basic traits of a pyroclastic flow (nuée ardente/glowing avalanche) eruption?
Concerning the following types of intermediate to felsic volcanic deposits, you should know the basic characteristics, and how they are formed: block lava, pyroclastic flow (welded ash-flow tuff), ash-fall tuff, and volcanic mudflow (lahar).
How is volcanic and other igneous activity distributed over the Earth’s surface, and where is most of it located?
What is meant by divergent plate igneous activity, convergent plate igneous activity, intraplate igneous activity, and what are hot spots?
Which major volcanic belts or volcanic island chains represent each of these, and which type is most common? (consult your notes for this last part).
A string of volcanoes that forms along a trench is called... an island arc
Iceland was formed over a... mid ocean ridge
volcanism any activity that includes the movement of magma toward or onto the Earth's surface
magma a body of molten rock found at depth, including any dissolved gases and crystals
lava magma that reaches Earth's surface
decompression melting melting due to a drop in confining pressure that occurs as rock rises
hot spots a concentration of heat in the mantle capable of producing magma, which rises to Earth's surface
intraplate volcanism igneous activity that occurs within a tectonic plate away from plate boundaries
volcano a mountain formed of lava and/or pyroclastic material
viscosity a substance's resistance to flow
-is responsible for climate changes
-creates new land (volcanoes, islands, and new sea floor)
-is involved in a rock type (igneous)
-provides chloride gas for salt water formation
-allows interior heat out
The mantle is solid because of... pressure
Magma forms in... the upper mantle and lower crust or mantle plumes
Conditions for the Formation of Magma
1. pressure is reduced - allows rocks to expand and melt (ex. divergent boundaries and hot spots)
2. temperature is increased - higher temperatures results from friction in subduction zones
3. change in chemical composition - the addition of water and gases lowers the melting point (ex. subduction zones)
-once magma forms, it rises to the surface because it is less dense than solid rock
Location of Volcanism
1. Divergent Boundary: creates new sea floor (islands), decompression melting, hot springs/geysers (ex. Iceland)
2. Convergent Boundary (subduction zones): creates island arcs and continental volcanic arcs, increase in heat, change in chemical composition (ex. Islands of Japan, Ring of Fire)
3. Hot Spots (Intraplate Volcanism): deep mantle plumes rise to surface creates holes in ocean floor and continents, form island chains, geysers, and hot springs, decompression, increase in temperature (ex. Hawaii; Yellowstone National Park)
Volcanoes Are... built from numerous eruptions and found on the ocean floor and continents (volcanic arcs)
The Nature of Volcanic Eruptions
-not all volcanic eruptions are the same
-it is mainly the characteristics of magma (both physical and chemical) that determine whether an eruption will be explosive, nonexplosive, or somewhere in between
-magma's chemical composition is different depending on where the magma formed
Factors of Volcanic Eruptions viscosity and dissolved gases
-determined by temperature and chemical composition
-lower temperature: more viscous (thick)
-higher temperature: less viscous (thin)
-high silica content: more viscous (clogs vents allowing pressure to build)
-low silica content: less viscous (doesn't clog vents)
-main force to propel the magma out of the vent; brings the magma with it
-more gas content (water, carbon dioxide, and sulfur dioxide): usually more explosive; usually at subduction zones
-Ex: tea kettle, shaken bottle of soda
crater a funnel-shaped pit at the top of a volcano
flank the side of a volcano
conduit an underground passage magma travels through
summit highest point; apex
vent an opening in Earth's surface through which volcanic materials escape
sill a flat piece of rock formed when magma hardens in a crack in the volcano
magma chamber a place under Earth's surface where magma rests
Volcanic Materials different eruptions produce different types of volcanic materials
Nonexplosive Eruptions usually produce lava flows; different viscosity, texture, and gas content (little)
Examples of Lava
(from thickest to thinnest)
-pa hoe hoe (ropey and wrinkly texture)
-aa (rough, jagged texture)
-pillow (cools underneath the water)
Explosive Eruptions usually produce lava and pyroclastic materials (tephra)
Pyroclastic Materials hot rock fragments ejected from a volcano; classified by the diameter of the particles
Types of Volcanoes
-there are different types of volcanoes
-classified by shape
-get shape by different types of eruptions (materials)
-shield (broad and slightly doomed)
-cinder cone (relatively small; formed from lava fragments that harden in the air)
-composite (large and explosive)
Factors the Affect How Magma Form
-increase in temperature
-reduction of pressure
-change in chemical composition
-formed from nonexplosive eruptions
-magma is not under a lot of pressure
-mainly composed of mafic lava
-very wide base and gentle slopes
-Ex: hot spot volcanoes
Mafic Lava thin lava in shield volcanoes that is dark in color with little silica
Cinder Cone Volcanoes
-formed from semi-explosive eruptions
-composed of pyroclastic material (cinders/lapilli)
-very narrow base and steep slopes
-form in clusters
-Ex: Paricutin (Mexico)
-also called stratovolcanoes
-form from explosive and nonexplosive eruptions
-composed of both lava and pyroclastic materials
-wide base and steep slopes
-Ex: Mt. Fuji (Japan), Mt. St. Helens (Washington), Mt. Etna (Italy)
Felsic Lava light in color, thick, high silica and gas content