VOLCANOES
What are the main differences between mafic and felsic magma in terms of silica content, temperature, and mineral composition?
Mafic magma: Low silica, high iron and magnesium, generally darker in color and hotter. It has relatively low viscosity.
Felsic magma: High silica, lower iron and magnesium, generally lighter in color and cooler. It has relatively high viscosity.
What is an earthquake? What happens when a fault suddenly slips?
An earthquake is ground shaking caused by the sudden release of stored elastic strain energy.
Stress builds up in rocks until they rupture or slip along a fault.
Energy travels outward from the rupture as seismic waves.
What are the three major rock types, and what processes form each?
Igneous: Formed by cooling and crystallization of magma or lava.
Sedimentary: Formed through deposition, compaction, cementation, or chemical/biological precipitation.
Metamorphic: Formed when existing rocks are altered by heat, pressure, and chemically active fluids without melting.
What is relative age dating? Does it tell us the numerical age of a rock?
Relative age dating determines whether a rock or geologic event is older or younger than another.
It establishes the sequence of geologic events.
It does not provide an actual age in years.
Approximately how old is Earth, and how do scientists know?
Earth is approximately 4.54 billion years old.
Scientists use radiometric dating of meteorites and the oldest Earth and Moon materials to establish this age.
What type of volcano is broad with gentle slopes and is built primarily from repeated flows of low-viscosity basaltic lava? Give a geographic example.
A shield volcano. Examples include Mauna Loa and Kīlauea in Hawaii.
Define the three important parts of an earthquake: focus (hypocenter), epicenter, and fault.
Focus (hypocenter): The location inside Earth where the earthquake rupture begins.
Epicenter: The location on Earth's surface directly above the focus.
Fault: A fracture or zone of fractures along which rocks move.
A rock contains visible, interlocking mineral crystals. What does this texture suggest about how the rock formed?
It is likely an intrusive igneous rock.
It cooled slowly beneath Earth's surface.
Slow cooling allowed larger mineral crystals to develop.
In an undisturbed sequence of sedimentary rock layers, which layer is the oldest? What principle explains this?
The bottom layer is the oldest.
The principle is the Law of Superposition.
What is a radioactive parent isotope? What is a daughter product? What does half-life mean?
Parent isotope: An unstable radioactive isotope that undergoes decay.
Daughter product: The isotope or product created through radioactive decay.
Half-life: The amount of time required for half of the original parent isotopes in a sample to decay.
At a convergent plate boundary, water released from a descending oceanic plate helps cause melting in the mantle above it. Why does this happen, and what type of magma and volcanoes commonly result?
Water lowers the melting temperature of mantle rock.
Subduction zones commonly produce intermediate-composition magma, such as andesite, and sometimes felsic magma.
Stratovolcanoes (composite volcanoes) are common in these settings.
What are two different ways or 'metrics' for classifying the intensity of earthquakes? Explain the data used in each. How are they different, how are they similar?
Richter / Magnitude Scale
Mercalli Scale
What type of information do geologists get from IGENOUS ROCKS? What can they tell us? How do we use them for science?
How else do we use them?
Geologic - radiometric age dating of rocks!
Tectonic settings (subduction vs hot spot, etc)
-Composition: what melted, magma source
-Texture: where/how it cooled
A fault cuts across three different rock layers. Are the layers older or younger than the fault? What principle explains this?
The rock layers are older than the fault.
The principle of Cross-Cutting Relationships states that a feature cutting across another rock or feature must be younger than what it cuts.
A mineral crystallizes and traps radioactive isotopes within its crystal structure. What event does radiometric dating typically measure? Why can heating or melting reset the clock?
Radiometric dating commonly measures the time since a mineral crystallized or cooled enough to become a closed system.
Heating or melting can allow parent or daughter isotopes to escape or redistribute.
This can reset the isotopic clock, meaning the resulting date may reflect the later heating or cooling event rather than the original rock formation.
Compare three common volcano types: cinder cones, stratovolcanoes, and Caldera volcanoes. Describe their structure, materials, and one characteristic hazard associated with each.
Cinder cones: Small, steep-sided volcanoes made primarily of loose volcanic fragments (scoria and tephra). Hazards include falling ash and volcanic bombs.
Stratovolcanoes: Steep-sided volcanoes built from alternating layers of lava and pyroclastic material. Hazards include pyroclastic flows, ash fall, and lahars.
Caldera: Large depressions formed when a volcano collapses following major magma withdrawal. Hazards include widespread ash fall and renewed explosive eruptions.
DOUBLE JEOPARDY!!!
What are the differences between P waves and S waves?
How are their properties used to determine the location of an earthquake's epicenter?
P waves arrive at a seismograph before S waves.
The difference in arrival times increases with distance from the earthquake.
Scientists use the time difference to calculate the distance from a seismic station to the epicenter.
Distances from at least three stations are used to triangulate the epicenter
What type of information do geologists get from METAMORPHIC rocks?
How do we use metamorphic rocks?
Geologic / radiometric age or TIMING of TECTONIC events like mountain building, deep burial, baking / contact
Tectonic settings: regional pressure (collision) = FOLIATION , depth, contact metamorphism (NON-Foliate)
USES: ore deposits, building/decorative stone (marble)
A granite pluton contains pieces of marble embedded within it. Which rock is older, and what principle explains this?
The marble fragments are older than the granite.
The principle of Inclusions states that fragments contained within a rock must be older than the rock containing them.
A rock sample originally contains 100 parent atoms. After two half-lives, how many parent atoms remain? What percentage has decayed?
After one half-life: 50 parent atoms remain.
After two half-lives: 25 parent atoms remain.
75% of the original parent atoms have decayed
A volcano erupts near an ice- or snow-covered summit. Explain how this can generate a lahar, why lahars are dangerous, and how the 2009 Mt. Redoubt eruption illustrates the challenges of making decisions about volcanic hazards.
Heat from an eruption melts snow and ice.
Meltwater mixes with ash, rock, and other volcanic debris to form a lahar.
Lahars are fast-moving, concrete-like flows that can travel long distances down river valleys.
They can bury infrastructure, destroy buildings, and kill people.
During the 2009 Mt. Redoubt eruption, lahars threatened the Drift River oil terminal.
Predicting the timing, volume, and path of lahars is difficult, making decisions about evacuations and facility closures challenging.
Why was the 2010 Haiti earthquake (Mw 7.0) so much more devastating than the stronger 2002 Denali Fault earthquake in Alaska (Mw 7.9)? Explain at least three contributing factors.
Haiti had a much larger population Emergency response capacity and infrastructure were limited. Most people died of cholera
The Denali earthquake occurred in a remote region of Alaska, with very little population or infrastructure exposed.
Damage often depends on population density, building construction, and socioeconomic factors
DOUBLE JEOPARDY !!
What do sedimentary rocks tell geologists? How do scientists use SEDIMENTARY rocks?
What are some resources or uses of sedimentary rocks?
Earth Surface through time - DEPOSITIONAL ENVIRONMENTS (oceans, dunes, glaciers, rivers etc)
FOSSILS - history of life on Earth
FOSSIL FUELS, collector fossils, building/decorative stone
Two separate outcrops contain similar rock layers and the same distinctive fossil assemblages. Explain how fossil succession and lateral continuity/correlation help geologists reconstruct the relative history of these rocks.
Fossil succession: Fossils occur in a recognizable sequence through geologic time. Similar fossil assemblages can be used to correlate and relatively date rock layers.
Lateral continuity: Sedimentary layers originally extend laterally and may be correlated across gaps caused by erosion or other interruptions.
Geologists use these principles to match rock units between locations and reconstruct regional geologic history.
Compare radiometric dating of rocks with radiocarbon dating. What materials are dated, what is measured, and what is the useful time range for carbon-14 dating?
Radiometric dating of rocks:
Measures the ratio of radioactive parent isotopes to daughter products.
Used on suitable minerals and rocks containing appropriate radioactive isotopes.
Can date events such as mineral crystallization or cooling.
Can provide ages ranging from thousands to billions of years, depending on the isotope system
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Radiocarbon dating:
Measures the amount of carbon-14 remaining in once-living organic material.
Carbon-14 is produced in the atmosphere when cosmic-ray-generated neutrons interact with nitrogen.
Living organisms continually exchange carbon with their environment.
Once an organism dies, carbon exchange stops and carbon-14 begins to decay.
Measures the time since the organism died.
Useful for dating material up to approximately 50,000 years old.