Exam 2 Flashcards
epicenter
the spot on the ground right above where the earthquake starts
hypocenter
the actual place underground where the earthquake begins
epicenter vs hypocenter
the epicenter is the point at the surface that lies directly above hypocenter
magnitude
the amount of energy the earthquake releases, measured on a scale (like the Ritcher scale)
intensity
how strong the earthquake feels in a specific area, including the damage it causes
magnitude vs intensity
magnitude is the total energy of the earthquake and doesn’t change based on where you are, while intensity describes what you feel in different places
P-waves (primary waves)
fastest seismic waves
travels in the earth
moves like a slinky (compress then release)
can travel through solids, liquids, and gases
S-waves (secondary waves)
slower seismic waves
travels in the earth
moves like a wave (up and side, side to side)
can travel through solids only
surface waves
waves that travel along the earth’s surface, causing the ground to roll or sway
Rayleigh waves and Love waves
what waves are responsible for most of the damage during an earthquake?
surface waves
seismograms
the record or graph that shows the seismic waves detected by a seismograph (the instrument that measures earthquakes)
it’s like an earthquake’s “fingerprint”
how do seismograms work?
a seismograph has a heavy weight attached to a pen, and when the ground shakes, the pens moves and draws a line on a rotating drum or digital system
p-waves show up first, followed by s-waves, then surface waves
what do seismograms measure?
amplitude = how strong the earthquake is
time between wave arrivals = how far away the earthquake’s epicenter is
p-waves arrive first, then s-waves, and the gap between them helps determine distance
amplitude
height of the wave
what information do you need to get the measurements you want using a seismogram?
at least 3 seismograms from different locations to pinpoint the earthquake’s epicenter (this is called triangulation)
divergent boundaries
places where 2 tectonic plates are moving away from each other
geologic formations from divergent boundaries
- mid-ocean ridges: form when plates separate and magma rises to create new ocean floor
- rift valleys: can form where plates diverge
convergent boundaries
where 2 tectonic plates are moving toward each other, often leading to one plate being forced beneath the other (subduction)
geologic formations from convergent boundaries
- mountain ranges: form when 2 continental plates collide
- volcanic arcs: form when an oceanic plate sinks beneath a continental plate
- ocean trenches: form when one oceanic plate subducts beneath another
transform boundaries
where 2 tectonic plates are sliding past each other horizontally
geologic formations from transform boundaries
- fault lines
- earthquakes are frequent
(no major landforms like mountains or trenches are typically created
normal faults
aka dip-slip fault
a fracture in the Earth’s crust where the rock above the fault moves down relative to the rock below
vertical movement
crust is being pulled apart
reverse/thrust faults
where the upper block of rock moves up and over the lower block
crust is being compressed
vertical movement
strike-slip fault
where the plates slide side by side past each other
horizontal movement
common at transform boundaries
what drives plate tectonics?
convection currents in the Earth’s mantle
hot material from the deep mantle rises, cools, and sinks back down, creating a cycle that moves tectonic plates
stratovolcanoes
large, steep-sided volcanoes built from alternating layers of lava flows and ash
steep slopes and tall, classic “volcano” shape
often produce explosive eruptions due
shield volcanoes
broad, gently sloping volcanoes formed by low-viscosity lava that spreads out over large areas
wide and flat with gentle slopes
eruptions are usually non-explosive
scoria cones
small, steep-sided cones made mostly of volcanic rock fragments (scoria or cinders)
typically short-lived and small in size
eruptions are moderately explosive but localized
flood basalts
huge, flat areas covered by layers of basalt lava from fissure eruptions, not from a central volcanic cone
massive, wide areas of flat lava flows
eruptions involve low-viscosity lava spreading out in sheets over great distances
calderas
large, basin-like depressions formed when a volcano collapses after a massive eruption
often form after explosive eruptions empty the magma chamber and the volcano collapses
volcanic domes
small, dome-shaped mounds formed by slow, viscous lava piling up near the vent
steep-sided domes formed by very thick lava
eruptions are often slow and can lead to dome collapse and pyroclastic flows
lahars
mudflows or debris flows made of volcanic ash, rock, and water that rush down the slopes of a volcano
lahars: hazard to humans
extremely destructive, can burry entire towns and sweep away buildings, bridges, and roads
fast moving and hard to escape
can happen long after an eruption
pyroclastic flows
fast-moving currents of hot gas, ash, and rock that race down the sides of a volcano during an explosive eruption
pyroclastic flows: hazard to humans
deadly, they can travel at speeds over 100 mph and reach temperatures over 1,000F
can obliterate everything in their path, including homes, forests, and roads
virtually impossible to outrun and cause instant fatalities due to intense heat and toxic gases
ash fall
ash particles ejected from a volcano that fall to the ground over wide areas
ash fall: hazard to humans
dangerous for breathing, especially for people with respiratory conditions
can collapse roofs if it accumulates and disrupt transportation
contaminates water sources and damages crops
volcanic gas
gases such as CO2, SO2 (sulfur dioxide), and H2S (hydrogen sulfide) released from a volcano
volcanic gas: hazard to humans
toxic and suffocating, can cause respiratory issues or death if inhaled in large amounts
CO2 can settle in low areas and displace oxygen, suffocating people and animals
SO2 can lead to acid rain, damaging crops, buildings, and water supplies
lava
molten rock that flows from a volcano during an eruption
lava: hazard to humans
slow-moving, but can destroy anything in its path (buildings, forests)
causes fires and burns, but it’s usually easy to escape if you’re far enough away
property damage is more common than direct harm to humans due to its slow flow
tephra
solid volcanic material, including ash, pumice, and larger rocks, ejected during an eruption
tephra: hazard to humans
larger tephra can injure or kill people and damage buildings if it falls in populated areas
smaller particles can cause breathing problems and disrupt air travel (can damage airplane engines)
high silica
thick, sticky, explosive eruptions (e.g. rhyolite)
found at convergent boundaries
low silica
thin, fluid, gentle eruptions (e.g. basalt)
found at divergent boundaries and hot spots
high temp in magma
more fluid, gentle eruptions (low viscosity, basaltic)
low temp in magma
thicker, more explosive (high viscosity, rhyolitic)
volatiles
dissolved gases in magma, like water vapor (H2O), carbon dioxide, and sulfur dioxide (SO2)
where do we find volatiles?
mainly in subduction zones and within magma
how do volatiles get there?
from subduction oceanic plates carrying water and sediments, dehydration of minerals, and melting mantle/crust
tsunami
a series of extremely long waves caused by a sudden displacement of the ocean
what causes tsunamis?
underwater earthquakes (most common), volcanic eruptions, landslides, and meteor impacts can cause tsunamis
how do tsunami waves evolve as they travel?
in deep water, tsunamis move quickly (up to 500-600 mph) but have low wave heights (often unnoticed)
as they approach shallow coastal areas, they slow down and the wave height increasing, creating large, destructive waves that flood inland
what can humans do to stay safe from tsunamis?
evacuate coastal areas if a tsunami warning is issued
move to higher ground or inland as quickly as possible
