Notes, summaries, assignments, exams, and problems for Geology

Seismic Portrait of Earth's Layers

Earth's layers are detectable as changes in seismic wave velocity with depth.

The boundary between the upper and lower mantle is visible at 660 km as a sudden change from rapidly increasing P- and S-wave velocities to slow or no change in P-wave and S-wave velocities.

The core-mantle boundary is apparent as a sudden drop in P-wave velocities, where seismic waves move from solid mantle to liquid outer core.

The boundary between the outer core and inner core is marked by a sudden increase in P-wave velocity after 5000 km, where seismic waves move from a liquid back into a solid again.

Crust–Mantle Boundary (Moho discontinuity)

Depth: Its depth is ~10 km under the ocean floor and ~35 km under the continents.

Discovery:

Radioactive Decay: Principles and Equations

If the decay rate is equal to λ, the probability that a given nucleus will decay in a small time interval dt is λdt. Therefore, if at any time we have P parent nuclei, the number that decay in the next moment is P(λdt).

The rate of change of parent nuclei (dP/dt) is proportional to the number of parent nuclei present:

dP/dt = -λP

This differential equation can be solved as follows:

• Separate variables: dP/P = -λdt
• Integrate both sides: ∫(dP/P) = -λ∫dt
• Resulting in: ln(P) = -λt + C

The boundary condition is found because we know that when t = 0, P = P₀ (the initial number of parent nuclei). Therefore, C = ln(P₀), and we can write the equation as:

ln(P) = ln(P₀) - λt

Rearranging this equation:

• ln(P)

Coastal Dynamics: Waves and Marine Erosion

Waves are fundamental forces shaping our coastlines. Their interaction with the shore involves two primary movements: swash and backwash.

Understanding Wave Dynamics

Swash and Backwash: The Basics

• Swash: When water rushes up the beach.
• Backwash: When water drains back down the beach.

Destructive Waves: Shaping Coastlines

Destructive waves are powerful forces that remove material from the beach. They are characterized by a weak swash and a strong backwash, pulling sand and pebbles back down the beach as the water retreats.

• Often steep, high waves that are close together.
• Crash down onto the beach.
• Come in very quickly, at a rate of 10 to 15 waves per minute.
• Also known as plunging waves.

Constructive Waves: Building

Coastal Erosion Processes and Hazards

Cliff erosion is a continuing process. Wave refraction causes eroding energy to wrap around jutting headlands, narrowing them and creating tombolos and offshore islands.

Site Selection and Construction Measures

1. Build 5 or more meters above normal high tide.
2. Build in a spot with numerous high dunes between the proposed building and the water.
3. Determine the rate of coastline erosion in the immediate vicinity.

Slope Stabilization Techniques

1. Reduction of slope angle.
2. Terracing.
3. Placement of additional supporting material at the base of the slope.
4. Removal of soil, rock, or artificial structures high on the slope to reduce the mass.

Signs of Slope Failure

1. Doors or windows stick or jam for the first time.
2. New cracks appear

Erosional Base and Graded Sand Units

Erosional base is in the head, and deposition is in the body.

Normal Graded Sand Unit (Ta)

Rapid deposition from suspension.

Planar Stratified Sand Unit (Tb)

Deposition on an upper stage plane bed, indicating flow deceleration, reduction of deposition rate, and establishment of a well-defined bed over which there was both bed load and suspended load movement.

Cross Laminated Ripple Unit (Tc)

Further decrease in flow velocity with an appreciable deposition rate.

The Overlying Planar Laminated Mud Unit (Td)

Deposition from the tail.

The Massive Mud Unit (Te)

Fallout from the turbulent buoyant plume.

Lakes: Palaeoclimate Indicators

Two key features of lakes:

1. They are among our best indicators of continental palaeoclimate.

Climograma

Un Climograma é un gráfico no que representamos simultaneamente os valores da temperatura media mensual, mediante unha liña, e os de precipitación media mensual, mediante barras verticais, dos doce meses do ano. No eixe vertical esquerdo situaremos as frecuencias de temperatura en oC (Graos Centígrados), tendo en conta se hai temperaturas inferiores a 0oC, pois nese caso haberá que deixar un espazo para representalas. As temperaturas medias mensuais están unidas por unha liña vermella 1.No eixe vertical dereito representaremos as precipitacións (en mm), tendo en conta as proporcións que debemos utilizar en función do total, sabendo que será necesario indicar o dobre do valor empregado no eixe vertical esquerdo. A diferenza... Continue reading "Climograma and Pollution: Environmental Impact in Spain" »

Abnormally Pressured Shallow Formations

Abnormally pressured shallow formations can result from upward fluid migration due to:

• Leaky fault
• Leaky cement or casing
• Improperly abandoned underground blowout

Steps Not Included in Well Drilling

Steps in well drilling do not include: building drilling equipment.

Drilling Rig Power System Selection

To select the power system of a drilling rig, one needs to consider the weight of the drill string.

Formation Fracture vs. Pore Pressure

Is formation fracture pressure always higher than formation pore pressure? Yes.

Causes Excluded from Abnormal Pore Pressure

Causes of abnormal pore pressure do not include: drilling.

When Not to Use Oil-Based Drilling Fluids

We would not use oil-based drilling fluids to increase safety,... Continue reading "Essential Principles of Petroleum Well Drilling" »

Celestial Mechanics & Timekeeping

Time Definitions and Earth's Motion

• Solar Day: The time from one local noon to the next; Earth rotates slightly more than 360° relative to the Sun.
• Sidereal Day: The time for a distant star to appear in the same position in the sky; approximately 4 minutes shorter than a solar day.
• Earth's Precession: A slow wobble in Earth's rotational axis, completing a cycle approximately every 26,000 years.

Moon Phases, Tides, and Orbit

• First Quarter Moon: Rises around noon, sets around midnight.
• Third Quarter Moon: Rises around midnight, sets around noon.
• Spring Tides: Occur during full and new moons, resulting in the highest tidal range.
• Neap Tides: Occur during first and third quarter moons, resulting in the lowest tidal

Understanding Earth's Diverse Climate Zones

Earth's varied landscapes are shaped by distinct climate zones, each with unique temperature, precipitation, and vegetation patterns. From lush jungles to arid deserts, these climates dictate the ecosystems and life forms found across the globe.

Equatorial Climate: Lush Jungles

Equatorial climates are characterized by temperatures near 25°C (77°F) and high rainfall, leading to lush vegetation that grows in distinct layers. These zones experience high levels of humidity and abundant water, with rivers often having a high discharge. A wide variety of insects, reptiles, and birds thrive in these vibrant jungle ecosystems.

Tropical Climate: Expansive Savannahs

Tropical climates feature high temperatures... Continue reading "Earth's Major Climate Zones Explained" »

Verticalist Theories and Fixism

Verticalist theories propose that movement in terrestrial materials is primarily vertical. These are considered fixist theories.

Key Aspects of Verticalist Theories

• Movement in terrestrial materials is vertical.
• They are fixist theories.
• Some related phenomena occur in the Earth's crust, such as Eustatic changes and Isostasy.

Understanding Eustatic Changes

Eustatic changes refer to global changes in sea level of greater amplitude than normal tides.

Causes of Sea Level Variation

These variations are driven by two main factors:

1. Variation in the volume of water in the oceans:
   • Glaciations: When ice sheets form, water is locked up, causing sea level to fall.
   • Thermal Contraction or Dilation: Changes in ocean temperature cause