Where is the thinnest lithosphere?

Oct 29, 2024

  1. Plate motions puts stress on boundaries + existing faults

The ridge grows continuously like fingernails 

  1. Stress builds where strong rocks or locked faults withstand it. Friction locks a fault, making its two sides stick together 

  2. Rocks and faults deform elastically (strain) in response to the building  stress

Strain- change in shape of rock due to stress (rubbing alongside each other like a transform boundary)

When a fault moves meters at a time it causes an earthquake 

  1. Earthquake occurs when stress exceeds ability of rocks to lock faults // stress finally builds higher than rock strength or faults friction and rock breaks or fault slips

EQ- brittle deformation

  1. Stress is released in the form of seismic waves that radiate out in 3 dimensions from where the rocks actually broke. Radiate in 3-D from focus

Focus- original starting point of earthquake 

  1. The rocks or faults elastically rebound and strain energy is released after earthquake 

  2. Plate motions puts stress on boundaries + existing fault (its a continuous cycle) 

Nov 5, 2024

Geological structures, deformation of rocks 


Sedimentary and most igneous rocks initially horizontal “structure” occurs when tectonic plates changes rock layers

Brittle deformation:

  • Takes place in lithosphere

  • Joints are vertical breakage of rocks when pressure on those rocks is reduced

Ductile deformation: 

  • Takes place in asthenosphere ~ 10-15 km below surface

  • Includes folds and foliation in metamorphic rock

Thickest lithosphere occurs at mountains 

Thinnest lithosphere occurs at ridges 

Faults break contiguous rock layers in 2


4 types of faults

  • strike - slip: no vertical motion. Layers move side to side, shear stress (transform boundaries) 

  • Normal Fault: footwall moves up, tensional stress (divergent boundaries)

  • Reverse: footwall moves down. Compressional stress (convergent boundaries)

  • Thrust Fault: same as reverse BUT angle of fault relative to earth's surface is shallower

Reverse Faults often flatten with depth to form thrust faults

Fold- Curve in shape of rock layer

Limb- sides of fold w/ less curvature

Hinge- Line where curvature is greatest 

Axial plane/surface - imaginary plane with successive hinges

Nov 7

  • Ductile Structures: Folds

  • Hinge - line where curvature is least

  • Axial plane/ surface - imaginary plane with successive hinges

  • Fold- curve in shape of rock layer

  • Limb -sides of fold w/ more curvature 


Folds are ductile 

Structure - rocks not broken but bent

Synclines- strata dip towards hinge

  • Dip (direction water would flow)

In the middle of dome, oldest rock is in the hinge

In the middle of basin, youngest rock at hinge


Mountain: vertical rise in surface of the earth, including volcanoes 

Tectonic plates and mountain building 

  • convergent and Divergent boundaries are associated with Vertical Motion 

  • Mountains for at boundaries with vertical movement (magma)


Oceanic- Continental convergent 

  • Sedimentary basin form adjacent to mountain range, cover the trench 

Continental- Continental convergent

  • Increase in density causes litho to sink in the asthenosphere

Divergent: continental rifting zone

Nov. 12, 2024

Numerical/ relative ages

Principles - relative dating


Uniformitarianism- Earth processes we observe today, must have occurred in deep past + recorded in rocks

Earth processes (can create sedimentary rocks)

  • Erosion 

  • Deposition

  • Earthquakes

  • Weathering 


Opposite of uniformitarianism catastrophes

Ex) meteorite hitting earth, extinction of dinosaurs 

Numeric Age - How old rocks are quantitatively  

Relative age- which rocks are older/younger qualitatively 

Tools to use to infer relative age

  • Original horizontality 

    • Sedimentary rocks are laid down horizontally because they settle in earth's gravity 

  • Superposition

    • Oldest rocks on bottom, younger rocks on top 

  • Lateral continuity 

    • Sedimentary rocks are laid in unbroken horizontal layers 

  • Geological structures (faults/ folds) are younger than the deformed rocks 

  • Cross Cutting

    • Rocks that cross cut other rocks are younger than the rocks they cross


Nov 14, 2024

We are living in a new geological epoch (or are we?)


Since the end of the ice age, 12000 years ago. Earth is in holocene epoch warming and stable climate

Athro= human

New epoch? Called Anthropocene (age of humans)

Humans have as much impact on the earth as natural processes like plate tectonics 

Human impact:

Climate change

Urbanization

Coastal development

Atomic Bomb

Habitat destruction - mass extinction? 

Nutrient Pollution

Currently not ready to be in geological epoch

Phanerozoic Periods:


The Phanerozoic eon is divided into 12 periods ^^. First defined by fossils 

Facies Fossil - tracks a particular environment through time

Index/ Zone Fossil- Widespread for short time interval, useful for biostratigraphy 


Biostratigraphy- using fossils to date rocks due to fossils having lived on earth for limited time 




Nov. 19,2024

Glaciers 

Where did these erratics come from?

  • Humans causing CO2 emissions which makes glaciers melt and also causes global warming. 

  • Erratics: boulder sized foreign rocks

How do glaciers transport erratics 

  • Weather erodes boulder from bedrock, 

  • then picks it up and transports it equater-ward. 

  • As climate warms, glacier retreats pole-ward, depositing boulder 

Louis Agassiz popularized glacial advances and retreats - (Ice Ages)

Geomorphology: the study of the topography of landscapes and how that topography would shape by earth processes

Difference between glacier eroded valleys and water eroded valleys

  • Shape : 

    • Glacier caves U shaped valleys steep sides as glacier erodes both sides 

    • Water carves V shaped valleys gently sloping sides erodes more evenly in periodic flooding 

Difference between drainage networks 

  • Glaciers create small roughly circular shaped lakes called kettle lakes. Formed when a chunk of ice breaks off a retreating glacier

  • Water creates stream like lakes 

Geomorphology continental glaciated landscapes 

  • Moraines - line of narrow hills 

    • Composed of unsorted + foreign sediments

    • Boulders to rock flower called “till” represent furthest extent of glacier 

  • Eskers- insects moraine numerous, at regular intervals

    • Formed as streams from melting glacier sorted sediments- sand, gravel, clays (closest to moraine —-> furthest from moraine) 

  • Outwash plain- unglaciated flat land where sediments from the melting glacier Accumulate

  • Tills make moraine 

  • Sand, Grave, sediment make eskers

  • Horn- mountain top eroded by glacier. Local maximum elevation 

  • Arete- ridges that separate glaciated valleys 

  • Cirque- bowl shaped valleys 

Rock flower- a fine powder of silt- and clay-sized particles that a glacier creates as its rock-laden ice scrapes over bedrock