Deformation of the Crust
Information in parenthesis is not required, but provided for additional clarification
Part 1 – Isostasy
Deformation
Asthenosphere
Gravity
Buoyant Force
Density
Equilibrium
Isostasy
Isostatic adjustments
Erosion / Weathering
Uplift
Deposition
Subsidence
Glaciers
Part 2 – Stress & Strain
Stress
Compression
Tension
Sheer stress
Strain
Brittle
Ductile
Strain Factors (5)
Units of stress (2)
Part 3 – Folds and Faults
Fold
Kinds of stress that tends to cause folds
Fold Anatomy
(Limbs)
(Hinge)
(Axial plane)
Overturned fold
Types of Fold
(Anticline)
(Syncline)
(Monocline)
Ridge
AppalachainMoutains
Fracture
Faults
Fault plane
Hanging wall
Foot wall
Normal fault
Reverse fault
Thrust Fault
Strike-SlipFaults
San Andreas Fault
Kinds of stress that cause faults
Normal
Reverse
Part 4 – Mountain Formation on Convergent Boundaries
Mountain
Mountain range
Mountain System
Mountain Belts
Features of Continent vs. Continent Collisions
Terrane accretion
Features of Ocean vs. Ocean Collisions
Features of Continent vs. Continent Collisions
Part 5 – Parts of Mountains
Folded Mountains
Plateaus
Erosion Plateaus
Lava field Plateaus
Fault-Block Mountains
Grabens
Dome Mountains
Volcanic Mountains
Hot spots
Deformation of the Crust
Information in parenthesis is not required, but provided for additional clarification
Part 1 – Isostasy
Deformation – Bending, tilting, and breaking of Earth’s crust
Asthenosphere – Solid plastic-like layer of the mantle on top of which the tectonic plates ride
Gravity – Universal force of attraction exerted by all matter in the universe (any object that has mass, generates a gravitational field = folds
space or creates a gravity wheel around it)
Buoyant Force – Upwards acting force exerted by a fluid that opposes an object’s weight (caused by differences in density between an object
and the fluid. If the object is less dense, it will float)
Density - A measure of how much matter (mass) is on a certain amount of space (increases it mass increases; decreases if space increases)
Equilibrium – When thing are balanced
Isostasy – Condition of gravitational and buoyant equilibrium between Earth’s lithosphere and asthenosphere (when the weight of the
lithosphere pushing down is balanced by the buoyant force of the asthenosphere and the mantle’s magma floating up)
Isostatic adjustments – Sinking or rising of the lithosphere to restore balance between buoyant and gravitational forces (if the weight of it is
too much; the lithosphere sinks until the buoyant force is strong enough to stop that; if the buoyant force is too strong; it will raise the
lithosphere until the buoyant force gets too weak to raise the weight any more)
Erosion / Weathering – Breakdown of rock into sediments by the chemical or physical action of water, wind, life, and ice.
Uplift – Rise in the lithosphere in response to reduced weight over an area of constant mantle buoyant force (i.e. Erosion reduces the weight of
an area that used to have a huge mountain)
Deposition – The process of gathering of large amounts of sand, mud, and/or gravel into larger bodies of water (common near rivers).
Subsidence – Sinking of the lithosphere in response to increase in weight over an area of constant mantle buoyant force (i.e. Deposition adds
weight to an area of the lithosphere making it heavier so it sinks)
Glaciers – Slowly-flowing frozen rivers
Part 2 – Stress & Strain
Stress – The amount of force per unit area that acts on a rock (or how much pressure the rock is under)
Compression – When stress squeezes and shortens a body
Tension – When stress stretches and pulls a body apart
Sheer stress – When stress distorts (twists, bends, breaks) a body by pushing different parts of the it in different directions
Strain – Change in shape or volume of rock resulting from stress that lasts too long or that is too intense
Brittle – Materials that respond to stress by breaking or fracturing easier than other materials
Ductile – Materials that respond to stress by bending or deforming without breaking
Strain Factors (5)
Rock composition (Ductile vs. Brittle)
Temperature (Colder = More brittle)
Pressure (More pressure = More brittle)
Intensity (Stronger stress = More brittle)
Exposure Time (Longer stress = More brittle)
Units of stress (2)
Metric System  Pascal (Pa) = 1 unit of force (in Neutons) divided by area (in square meters)
British System  PSI = 1 unit of weight (pounds) divided by area (in square inches)
Part 3 – Folds and Faults
Fold – A form of ductile strain in which rock layers bend
Kinds of stress that tends to cause folds – Compression (Most common); Sheer stress (less common)
Fold Anatomy
(Limbs) – Sloping sides of the fold
(Hinge) – Bend in the rock layers where limbs meet on a fold
(Axial plane) – Mid-line of the fold, when a fold is symmetric
Overturned fold – When a fold appears to be lying on its side (Most folds seem vertical)
Types of Fold
(Anticline) – Fold in which oldest layer is in the center of the fold (arc shaped like mountains)
(Syncline) –Fold in which the youngest layer is in the center of the fold (bowl shaped like valleys)
(Monocline) – Fold in which both limps are horizontal or almost horizontal
Ridge – Large fold common near mountains
AppalachainMoutains – Landform or rock formation of ridges and valleys resulting from the collisions that formed Pangea
Fracture – A form of brittle strain;A break along which there is no movement of the surrounding rock
Faults – A form of brittle strain; Break in a body of rock along which block slides relative to another
Fault plane – The surface or plane along which the motion occurs in a fault
Hanging wall – Rock above the fault plane
Foot wall – The rock bellow the fault plane
Normal fault – A Fault in which the hanging wall moves downward relative to the footwall (i.e. The Great Rift Valley of East Africa where a
series of parallel fault lines form steep, step-like rock formations)
Reverse fault – A Fault in which the hanging wall moves upward relative to the footwall (common in steep mountain ranges like the Rockies
and the Alps)
Thrust Fault – Special type of reverse fault in which the fault plane is at a low angle or nearly horizontal (common in steep mountain ranges
like the Rockies and the Alps)
Strike-SlipFaults – Horizontal movement between rocks in a direction parallel to the fault plane. They slide (i.e. San Andreas fault, which is
near a transform boundary; They are also common in Fracture Zones along the mid-ocean ridges)
San Andreas Fault – Large strike-slip fault that shows that fault can sometimes be as large as a state and can occurs in a system of interrelated cracks on the lithosphere
Kinds of stress that cause faults
Normal – Tension
Reverse – Compression
Part 4 – Mountain Formation on Convergent Boundaries
Mountain – A fold or accumulation of sediment on the Earth’s lithosphere
Mountain range – A group of adjacent mountains that are related to each other in shape and structure
Mountain System –A group of adjacent mountain ranges (i.e. Appalachian – Great Smoky; Blue Ridge; Cumberland; Green (Eastern North
America)
Mountain Belts – The 2 major mountain systems of the Earth: Euroasian-Melansian Mountain Belt(Indo-Pacific Islands; Himalayas;
Southern Europe; Alps; Ural Mountains in Africa) &Circum-Pacific Mountain Belt ( Ring around the pacific that includes Pacific Islands;
New Zeland; Papua New Guinea; Japan) Northeastern Russia; Alaskan Islands; Alaska; Rockie Mountains; Central Mexico; Cuba; Haiti;
Jamaica; Puerto Ricol Northern South America; Andes)
Features of Continent vs. Continent Collisions
 Trench (Result of the subduction of the thinner but denser oceanic plate underneath the less dense but thicker continental plate)
 Fractures / Faults (especially Thrust & Reverse Faults)
 Earthquakes (Result sudden from plate vs. plate motion and motion along faults common in these areas; these earthquakes often
cause tsunamis)
 Mountain Range on land (Folding & uplift of lithosphere as a result of the collision)
 Volcanoes (Melting of subducting plate produces magma that rises because of the pressure of the heat of the magma and the
weight of the continental crust; magma rises using fractures/faults on the colliding continental crust)
(Note: Earthquakes at these boundaries often cause tsunamis)
(Note: This means that the Mountain Range is often populated by active volcanoes)
Terrane accretion –Sea mounts;atolls ;or large pieces of crust that broke off continentsthat get scraped off the subducting plate and added to
the other
Features of Ocean vs. Ocean Collisions
 Trench (Result of the subduction one oceanic plate underneath another; These will form the deepest trenches in the world)
 Island Arc (Folding & Uplifting of the lithosphere as result of the collision; essentially a mountain range that rises from the sea
floor to breach the surface of the ocean)
 Fractures / Faults (especially Thrust & Reverse Faults)
 Earthquakes (Result sudden from plate vs. plate motion and motion along faults common in these areas; these earthquakes often
cause tsunamis)
 Volcanoes (Melting of subducting plate produces magma that rises because of the pressure of the heat of the magma and the
weight of the other plate; magma rises using fractures/faults on the colliding plate)
(Note: Trenches at these boundaries are the deepest regions of the crust)
(Note: Earthquakes at these boundaries often cause tsunamis)
(Note: This means that the island arc is an Arc of Volcanic Islands)
Features of Continent vs. Continent Collisions
 Subduction zone
 Fractures / Faults (especially Thrust & Reverse Faults; these are specially common in these collisions)
 Earthquakes (Result sudden from plate vs. plate motion and motion along faults common in these areas)
 2 Mountain Ranges with Deformed Sea Floor Valley in between (Uplifting & Folding of crust on both continents as they merge in
the collision; In between them the ocean floor that once separated them forms a valley filled with deformed sea floor sediments)
 Magma Chambers (Melting of subducting plate produces magma that rises because of the pressure of the heat of the magma and
the weight of the continental crust; magma rises using fractures/faults on the colliding continental crust; magma does not usually
break the surface because of size and weight of mountain ranges
(Note: These form the largest mountain ranges in the World)
(Note: These form the largest and most active thrust faults of the world)
(Note: Volcanic activity is limited and often trapped underground by size and weight of mountain ranges)
Part 5 – Parts of Mountains
Folded Mountains – A mountain that forms when rock layers are squeezed together and uplifted (most mountains start off like this; they are
born by the processes described above)
Plateaus – Large, flat areas of rock high above sea level that form when thick, horizontal layers of rock are uniformly uplifted without faulting
or folding (typically form near mountain ranges)
Erosion Plateaus – Large areas of rock eroded into plateau shape
Lava field Plateaus – Layers of molten rock that harden and pile up on Earth’s surface
Fault-Block Mountains – Mountain that forms where faults break Earth’s crust into large blocks and some blocks drop down or rise up
relative to others (in other words when fold mountains and fault lines combine in large scales)
Grabens – When gaps between fault-block mountains form long, narrow valleys
Dome Mountains – Circular or elliptical, almost symmetrical elevation or structure in which the stratified rock slopes downward gently from
the central point of folding (look like perfect anticlyne fold; form by gentle tectonic push )
Volcanic Mountains – Mountains formed by volcanic processes (When magma erupts to the surface it often does so by first bending the
surface from underneath; Volcanic mountains also form when magma piles up from a central location over many years; examples of volcanic
mountains can be seen within folded mountain regions, island arcs, mid-ocean ridges, and hot spots)
Hot spots – Volcanic active areas far from tectonic plate boundaries