Volcanic, Tectonic and Orogenic

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Transcript Volcanic, Tectonic and Orogenic

Endogenic Processes:
Volcanic, Tectonic and Orogenic
– Eruptions, Earthquakes, Tsunamis
– a major subfield of geography and Geology
– Study of landforms – their origin and
change over time and space
Geomorphic Processes: Physical processes which create
and modify landforms on the surface of the earth
 Are landform changes
gradual or abrupt?
 These processes operate
in episodic manner – with
earthquakes and volcanic
eruptions causing a
punctuated equilibrium
Geomorphic Processes:
 A. Endogenic
 B. Exogenic
 Relates closely to the
Rock Cycle 
A. Endogenic Processes
Endogenic Processes are large-scale landform
building and transforming processes
– they create relief.
1. Igneous Processes
a. Volcanism: Volcanic eruptions  Volcanoes
b. Plutonism: Igneous intrusions
2. Tectonic Processes (Also called Diastrophism)
a. Folding: anticlines, synclines, mountains
b. Faulting: rift valleys, graben, escarpments
c. Lateral Faulting: strike-slip faults
Earthquakes  evidence of present-day tectonic activity
Igneous Processes
– involving eruptions or emplacements of molten magma from
the earth’s mantle (extrusive and intrusive igneous rocks)
Volcanism : It refers to the extrusion of rock matter from earth’s
subsurface to the exterior, and the creation of surface terrain features –
Volcanoes are mountains or hills that form in this way.
How Volcanoes are Formed
 About 95% of active volcanoes occur at the plate
subduction zones and at the mid-oceanic ridges.
Subduction is a process of plate tectonics where one lithospheric plate
is pushed below another.
 The other 5% occur in areas associated with lithospheric
hot spots.
Where are Volcanoes Found?
Where are Volcanoes Found?
Convergent Plate Boundaries  Subduction Zones
Oceanic-oceanic  island arcs
Aleutian, Kurile, Marianas, Tonga
Oceanic-continental  active continental margins
South America, North America, Central America, Kamchatka
Divergent Plate Boundaries  Mid-Oceanic Ridges
and Rift Valleys
Continental-Continental  Continental rifts
East Africa, Red Sea-Gulf of Aqaba
Oceanic-Oceanic  Oceanic rifts
Mid-oceanic ridges, spreading sea floors, volcanic islands
Iceland, Azores
Intraplate  “Hotspots” or “Mantle Plumes”
Oceanic islands
Hawaii, Emperor Seamount Chains – Pacific Ocean
Yellowstone, Wyoming, USA
A volcano is generally a conical shaped hill or mountain –
some active, others dormant.
 Built by accumulations of lava flows, and tephra (or
fragmented rock material ejected by a volcanic
explosion -- also called pyroclastic material, ranging
in size from volcanic ash, cinder to volcanic “bombs”
 Volcanic eruptions
 Explosive vs. Effusive, depends
mainly on temperature and chemical
differences in the magma
 silica-rich felsic magma has greater
potential for explosive eruption
 basalt-based mafic magma leads to
more effusive eruption
Volcanic Landforms
Volcanic activity gives rise to such topographic features as:
 Lava Flows  ropy pahoehoe, and blocky aa
 Volcanic Islands
• related to hot spots, as in Hawaii
• related to divergent plates and seafloor spreading, as in Iceland
 Volcanic Mountains
 (a) Shield, (b) Cinder Cone, (c) Composite Cone or Stratovolcano
and (d) Plug Dome volcanoes + (e) Caldera
Shield volcanoes are
volcanic mountains built
up by the eruption of
fluid, basaltic lava flowing
out of a central vent.
They have broad bases
with very gentle slopes
The largest shield
volcano on Earth is
Mauna Loa in Hawaii
which rises from its
base on the seafloor
to a height of 17 km
(10.5 miles).
A cinder cone is a steep, conical
hill of volcanic fragments that
accumulate around and
downwind from a vent
Cinder cones range in size from
tens to hundreds of meters tall.
Amboy Crater, southeastern
Stratovolcanoes are very tall,
1000s of feet, and are typical
cone-shaped mountains
Produced by alternating layers of
felsic and mafic magmas, hence
stratas  and “Stratovolcano”
Most have snow, ice and even
glaciers at top because of their
Eruptions are mostly explosive,
but often also effusive
Examples: Mt. Shasta, Mt. Hood,
Mt. Rainier, Mt. Fujiyama, Mt. St. Helen
Mt. St. Helens
a typical composite volcano
(before and after 1980 eruption)
These volcanoes produce thick pasty lava
The lava cools into angular blocks after it is slowly
squeezed out of the vents
Mt. Lassen, northern California
The most explosive type of volcano is the caldera. The cataclysmic
explosion of these volcanoes, and subsequent subsidence, leave
a huge circular depression on Earth's surface.
Wizard Island and Crater Lake,
Lake Toba, Indonesia
Largest recognized caldera
Lake Toba, Indonesia
Erupted ~ 75,000 years before
present (ybp)
Measures 20 miles by 60 miles
Ejected 2500 km3 of material into
Long Valley Caldera
Lava flows of the Mono-Inyo
Craters volcanic chain in Long
Valley Caldera, California
The most recent eruptions from
this chain occurred about 250 and
600 years ago
Scientists have monitored geologic
unrest in the Long Valley,
California, area since 1980
The central part of the Long
Valley Caldera had begun
actively rising
Unrest in the area persists today
 Igneous intrusions, plutons, are eventually exposed at the surface, and
tend to stand higher than surrounding landscape.
 Stocks, Batholiths, Laccoliths, Sills, Dikes, and Volcanic Necks.
Devil’s Tower, Wyoming: Volcanic Neck
Morro Rock:
Volcanic Necks in California
Tectonic Processes
– Also called Diastrophism, it relates to:
• Tectonic forces, which not only move the lithospheric
plates, but also cause bending, warping, folding,
tilting, and fracturing of earth’s crust at various scales.
• Such deformation
(nature, orientation,
inclination and
arrangement) of
affected rock layers
is recorded in the
rock structure
Rock Structure
Near Golden Gate Bridge
San Francisco, CA
• Relative to adjacent rock masses, the rock layers may also
become offset, uplifted, or down-dropped
• Orientations of inclined rock layers are measured by their
strike (compass direction) and dip (angle)
Three Types of Tectonic Force
and associated types of structural deformation
Tensional Tectonic Forces
• Faulting
-- Normal faults
and Fault blocks
– Rift valleys (Rio Grande in NM and CO, East Africa, and Dead Sea)
– Escarpment (scarp) – fault scarps
Graben & Horst Topography
– Basin and Range Region of western U.S.
Tilted fault blocks
-- Death Valley, California
Compressional Tectonic Forces
• Folding
– anticlines, synclines
– overturn
-- recumbent fold
• Faulting
– reverse fault
-- thrust fault (overthrust)
Shearing Tectonic Forces:
Lateral Faulting
– strike-slip fault vs. dip-slip faults
– San Andreas Fault
San Francisco area,
after 1906 earthquake
San Andreas Fault
along the Carrizo Plain
in central California
Earthquakes : Evidence of present-day tectonic activity
What is an Earthquake?
• A wave-like sudden vibration or trembling in the Earth – a
form of wave energy that travels through the bedrock
• Happens when accumulated tectonic stress is relieved
through sudden, lurching movement of crustal blocks
along a fault line
The motion is caused by quick release
of seismic waves which travels away
from a sub-surface point of sudden energy
release – the Focus
Epicenter is located at the earth’s surface
immediately above the focus
Although most earthquakes occur along plate boundaries
or fault lines, they can also be triggered by volcanic eruptions
or magma beneath the surface. Earthquakes can precede or
accompany volcanic eruptions.
Earthquakes shock waves or Seismic Waves travel through
the body of the Earth (BODY WAVES) and along the surface
Seismic Body Waves are of two types:
P-waves (Primary waves) are faster, traveling at about 5 km/s
• These high-frequency, short waves move through solids and liquids
• Ground is moved forward and backward as the wave passes through
S-waves (Shear/Secondary waves)  half the P-wave speed
• High-frequency, short transverse waves move only through solids
• Ground is moved upward and downward as the wave passes through
Surface Seismic Waves include Love and Rayleigh waves
 Love waves vibrate the ground horizontally – A kind of
‘swaying’ motion is felt at the surface
 Rayleigh waves are the slowest of all seismic waves – the
ground moves up and down in response to Rayleigh wave
Measuring Earthquakes
 Instruments are used to record the magnitude of energy
released as well as the intensity of shaking by earthquakes
 Seismographic equipment measures ground motion as a
function of time
Two basic methods of measuring earthquakes are:
Richter’s Magnitude Scale:1935, quantitative, objective, 1 – 10
+ Moment Magnitude Scale – accounts for surface area
affected and faulted rock’s strength (Modified Richter)
Mercalli’s Intensity Scale: qualitative, subjective, I - XII
Where Do Earthquakes Occur?
• Most earthquakes occur in linear belts, along tectonic plate boundaries
• 80% occur around the Pacific Ocean Basin (along the Pacific Ring of Fire)
Global Distribution of Magnitude 4.5+ Earthquake Activity, 1990-1995
Rupture zones along the San Andreas Fault for each of
the three major earthquakes:
January 1857 Fort Tejon ▪ April 1906 San Francisco;
October 1989 Loma Prieta
 January 17, 1994 4:31 a.m. 6.7 on Richter Scale
 Earthquake occurred on a blind thrust reverse fault (Oak
Ridge Thrust Fault system) and produced the strongest
ground motions ever recorded in North America
Past Earthquakes
in Southern California
 Displacement on either side of fault
Vertical and horizontal displacement on Earth’s surface
 Seiches
Movement in an enclosed body of water due to intense
shaking – Water may actually ‘slosh out’ of the bay or
 Liquefaction
Groundwater rises to surface and destabilizes soils –
buildings collapse
 Tsunami
Seismic sea wave generated by earthquake on ocean floor
 Sumatra, Indonesia, 2004
 Japan, 2011
 Cascadia Subduction Zone
Monster Quake + Tsunami ?