The Dynamic Earth: A Comprehensive Guide to Geology

Posted on Oct 26, 2024 in Geology

Summary of Geology

Theory of Plate Tectonics

The lithosphere is divided into plates that move under a layer with plastic characteristics called the asthenosphere.

Convection Currents in the Mantle

• 
• Engine that generates currents: Earth’s internal heat

Types of Plate Boundaries

Convergent Boundaries

At convergent boundaries, there is destruction of the lithosphere. These boundaries are generally located in areas with trenches where the denser lithospheric plate subducts. For this reason, this area is also called a subduction zone. Trenches are located in areas of transition from continental crust to oceanic crust or between areas of oceanic crust. Convergent boundaries can also occur between continental plates, as happened when the Indian plate collided with the Eurasian plate.

Divergent Boundaries

At divergent boundaries, there is formation of new lithosphere. They are located at mid-ocean ridges and are areas where new oceanic crust is generated. Mid-ocean ridges are extensive mountain chains usually with a central valley called a rift, whose depth varies between 1,800 and 2,000 meters, with an approximate width of 40 km and with stepped walls cross-cut by faults. In rapidly spreading mid-ocean ridges, like in the Pacific, there is no central valley.

Conservative Boundaries

At conservative boundaries, there is no creation or destruction of lithosphere. They include certain faults, called transform faults. These faults cut across mid-ocean ridges and along them, there is no destruction or spreading, but only one plate sliding past another.

Oceanic Reliefs

Theme 2: The Solar System

Formation and Constitution

Theories about the Origin of the Solar System

Chance Collision Between Two Stars (Catastrophic Theory)

• The sun would have formed first, with no planets revolving around it.
• A wandering star in space would have shocked the Sun, ripping off small pieces.
• These pieces, after condensing, would have given rise to the planets.
• Rejected because: the temperature would be too high to allow condensation of matter.

Two Stars Would Have Approximated

• By the action of their gravitational fields, the stars would be deformed.
• As a result of deformation, small portions would be pulled out, thus forming the planets.
• Rejected because: a star’s gravity field would not be strong enough to tear off pieces of the Sun, and the temperature would be too high to allow condensation of matter.

Nebular Hypothesis

• Starting point: a gigantic, interstellar cloud of matter composed of gases enriched with heavy elements that resulted from the “Big Bang”.
• Condensation of matter: heating of the cloud core and rotation.
• Increase in the speed of rotation, with subsequent flattening.
• Agglutination of the particles that constitute the central nebula and the formation of a star: the proto-sun (start of thermo-nuclear reactions).
• Zonation of dust, according to the distance from the Sun: densest elements are concentrated near the Sun (terrestrial planets), less dense elements (hydrogen and helium) are relegated to the outer zone of the cloud (gas giants).
• Arguments for:
  • All solar system bodies have the same age (4.6 billion years).
  • The planetary orbits are nearly circular ellipsoids (except Mercury) and they are all virtually on the same plane.
  • The rotary motion of the planets (except Venus and Uranus, which are retrograde) is counterclockwise.
  • The density of the planets nearest the Sun is higher than the outer planets.

Geocentric Theory vs. Heliocentric Theory

• Geocentric theory:
  • The Earth was the center of the Solar System.
  • Proposed by Aristotle and Ptolemy.
• Heliocentric theory:
  • The Sun was the center of the Solar System.
  • Proposed by Copernicus and Galileo Galilei.

Constitution of the Solar System

• A star: the Sun
• 8 major planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune; characteristics:
  • 
• Asteroids: located between Mars and Jupiter in the asteroid belt. Composed of an alloy of iron and nickel.
• Dwarf planets: celestial bodies that orbit around the Sun; assume a rounded form, do not have an orbit clear of other celestial bodies.
• Small bodies: asteroids are small bodies that did not form into a planet because of the gravity fields of Mars and Jupiter; they occupy a broad belt of space between the orbits of Mars and Jupiter. Comets are spheroidal bodies with eccentric orbits, consisting of: a core (rocks, frozen gases, and water), a coma (loose solid particles released when near the sun), and a tail (gas driven by the solar wind). Meteoroids are bodies from space that can reach our planet:
  • Meteors do not reach the Earth’s surface, only form a luminous trail. They heat up during entry into the atmosphere due to friction.
  • Meteorite: hit the ground. Resist friction caused by entry into the atmosphere. Upon reaching the surface, they form impact craters. Types:
    • Siderites or iron meteorites, consisting of alloys of iron and nickel.
    • Stony meteorites, composed of silicates.
    • Stony-iron meteorites: they are hybrid metal-rock, consisting of alloys of iron, nickel, and silicates.

Accretion and Differentiation

Sequence of Events

• The Earth would have originated from the accretion of nebula particles that collided due to gravitational attraction. During accretion, the Earth’s temperature was rising steadily.
• The energy from the impact of planetesimals was converted into heat, which would accumulate inside the protoplanet. This energy was not entirely dissipated into space because the protoplanets continuously collided with planetesimals that covered them again and also converted their impact energy into heat energy.
• The size of the protoplanet increased, and this increase also increased the pressure to which the materials were subjected to compression. The pressure of the materials, associated with the progressive increase in depth, raised the temperature of the protoplanet’s material composition.
• The temperature reached the melting point of silicates, iron, and nickel, which formed the Earth protoplanet. Then, differentiation began, i.e., the separation of the Earth’s constituent materials.
• The denser materials, iron and nickel, migrated, driven by density differences, toward the center of the Earth, where they formed the core. The materials with intermediate density, silicates associated with iron and nickel, occupied the middle zone of the Earth, giving rise to the mantle. Finally, the least dense silicates reached their solidification temperature, forming the primitive crust (brittle and fragile). The core, due to high temperatures and heat production, still remains, even today, in a liquid state.
• The merging of Earth materials led to the differentiation of the Earth and the formation of three major lithological zones: the crust, mantle, and core.
• 

The crust was the first layer to solidify due to its proximity to the low temperatures of space. However, due to the lack of atmosphere, it was still being bombarded by countless meteorites, whose impact with the thin, newly formed surface originated volcanic activity, which released large amounts of lava and water vapor. The water vapor, upon condensation, originated the first rains on the planet, which began the formation of the primitive oceans. Simultaneously, the formation of the primitive atmosphere began, and the first forms of life emerged in the primitive oceans.

Manifestations of Geological Activity

On Earth, Earth and Venus are both geologically active planets, while Mercury and Mars are geologically inactive planets. A planet is considered geologically active when it currently or in the recent past exhibits earthquakes, volcanic activity, or tectonic movements. A planet is considered geologically inactive when, for a very long time, it has had no active geological phenomena such as earthquakes, volcanic activity, or tectonic movements. Tectonic movements, in turn, are greatly responsible for the existence of the seafloor and its age (less than 200 million years). The ocean depths are the result of a balance between rifts and subduction zones. In the rift, the ocean floor is formed by a volcanic fissure, which causes the oceanic plate to grow in size, which, therefore, will be “forced” to subduct to maintain a constant surface area of the Earth.

Any form of geological activity requires a modifying agent, which can be either internal or external to the planet.

Modifying Agents

Note:

• On Earth, water is the main factor in the renewal of the crust because of its cycle (hydrologic cycle), which is “driven” by the Sun.
• To find data on the first 700 million years, erased by erosion (on Earth and Venus), we refer to geologically “dead” planets.

The Earth-Moon System

The Moon is the Earth’s natural satellite (a body describing orbits around a primary planet), with reduced dimensions compared to Earth (4 times smaller). It is thought that its formation is related to a body smaller than Earth that collided with Earth early in its history. The Moon has no atmosphere, due to its low mass and gravitational force, or liquid water and, therefore, no erosion, so the lunar surface is largely unchanged. Due to its inactivity, the Moon seems to have preserved a large part of its primitive features. For this reason, by studying the Moon, we can understand a little of Earth’s history. The Earth’s satellite preserves the marks of events before the formation of our continents, constituting a memory of what the Earth would have been like during that period. The Moon and Earth interact with each other, influencing their movement in space. Earth’s day length is determined by the presence of the Moon, and changes in the Moon’s position relative to Earth cause changes in day length and lunar months. Between Earth and the Moon, there is a strong gravitational coupling, and they are thus considered by some scientists as a double planet system.

Changes in the force of gravity exerted by the Moon on Earth determine the variation of ocean tides. The force of attraction between the Earth and Moon leads to a decrease in the speed of Earth’s rotation, which leads to an increase in the duration of daylight hours on Earth. Each terrestrial day increases by 0.0018 seconds per century.

Since the Moon has the same origin as its main planet and formed almost at the same time, we can understand the pace of events. The following table outlines the sequence of events that happened in the origin and evolution of the Moon:

The Moon, like Earth, has two types of geomorphic formations: highlands and maria. The names of these lunar formations are due to their perceived similarity with Earth’s features.

The Moon has no erosion due to the lack of atmosphere and liquid water, yet there may be a breakdown of rocks due to large temperature variations. The Moon has a daily temperature variation that can range from -180°C to +120°C. This temperature variation can lead to the fracturing of rocks, just like a cup that comes out of the oven and is placed on a cold surface. The fragments generated by thermal fragmentation can slide down lunar slopes, this being the only means of modifying the lunar surface, besides meteorite impacts and their effects.

The absence of geomorphological changes on the Moon allows it to retain the characteristics of the time of its formation. The Earth, by having agents of erosion, volcanic activity, and tectonic movements, is constantly changing, so we cannot directly observe the characteristics of the early Earth. The Moon, by being contemporary with Earth and having remained largely unchanged, allows us to obtain data on the early Earth. A great deal of information on the composition and morphology of the Moon was provided by the Apollo missions, which allowed the collection of lunar material.

Theme 3: The Earth, a Planet to Protect

The Face of the Earth

Continents

Cratons (Stable Geological Areas)

• Shields – cores of magmatic and metamorphic rocks with ages of approximately 600 million years or older.
• Interior platforms – composed of younger rocks that retain their original horizontal position.

Mountain Ranges

• Old
• Recent

Continental Margins

Oceans

• Abyssal plains
• Ocean trenches (convergent zones)
• Mid-ocean ridges
• Rifts (divergent zones)

Human Interventions in the Subsurface

Water

Sources of Pollution

• Effluents
• Oil spills
• Industry (acid rain)
• Agriculture (pesticides and herbicides)

ETA: Water Treatment Plant

This is where water is treated to remove organisms and chemicals before being distributed to populations.

WWTP: Wastewater Treatment Plant

It treats used water, improving its quality, but not making it potable, before discharging it in a less environmentally damaging way.

Measures for Saving Water

• Place bottles in the toilet tank.
• Take showers instead of baths.
• Use water from cooking to water plants.
• Close the tap while brushing teeth and shaving.
• Repair dripping taps, avoiding leakage.
• Use tap aerators.
• Wash clothes/dishes only when the machine is full.
• Use “smart” cisterns.

Soil

Sources of Pollution

• Deforestation
• Farming
• Overgrazing
• Industry (acid rain)
• Human construction (soil sealing, causing floods)

Fossil Fuels

What are they?

Fossil fuels generate energy when burned; they formed millions of years ago from the accumulation of organisms. Examples: oil (animal organisms), coal (plant organisms), and natural gas.

Why are they bad?

• They are finite.
• The greenhouse gas (GHG) emissions released by burning them degrade the environment:
  • Acid rain
  • Greenhouse effect

Geological Resources

What are they?

They are the natural assets that exist in the Earth’s crust and that, due to their concentrations at a particular location, can be extracted and used for the benefit of humankind.

Renewable vs. Non-renewable

• Renewables: are generated by nature at a rate equal to or higher than the rate at which they are consumed. Examples: geothermal, tidal, water, etc.
• Non-renewable: are generated by nature at a much slower pace than the rate at which they are consumed by humans. They are, therefore, limited resources that will eventually run out. Geological resources are non-renewable, except for water and the Earth’s internal heat. Examples: oil, coal, wolframite, etc.

Energy Resources

• They are fundamental for the various activities of human beings.
• The development of industrialized societies and technology has exponentially increased energy consumption.
• Most of the energy consumed by societies today comes from fossil fuels.

Fossil Fuels

• Coal, oil, and natural gas are non-renewable energy resources and are rapidly approaching exhaustion.
• The energy they contain is stored in the chemical bonds of organic compounds, subject to complex transformations over long periods.
• Coal is mainly used in power stations to produce energy. Oil and natural gas are used as fuels. Oil also has numerous industrial uses.
• The burning of fossil fuels causes various environmental problems:
  • Releases sulfur dioxide into the atmosphere, which, when combined with atmospheric water vapor, produces H₂SO₄ (sulfuric acid), which precipitates as acid rain. Acid rain lowers the pH of the soil and waterways, killing organisms and causing ecosystem imbalance.
  • Also releases large amounts of CO₂ into the atmosphere. The increase in atmospheric CO₂ contributes to the increase in greenhouse gases and, hence, global warming of the planet.
  • The extraction of coal from mines and the extraction of oil from wells can cause contamination of soil and water.

Nuclear Energy

• The production of nuclear energy is based on the controlled fission of the element uranium in nuclear reactors.
• This reaction releases large amounts of energy in the form of heat; this heat is used in the vaporization of water, which, in turn, is used for energy production.
• Disadvantages:
  • Risk of accidents, leaking radiation.
  • Production of radioactive wastes that pose serious problems for treatment and storage.
  • Thermal pollution of water.
  • Risk of terrorist action.

Geothermal Energy

• The Earth’s internal heat is a source of energy that can be concentrated locally.
• When there is a source of magma relatively close to the Earth’s surface, there is heating of fluids, usually water, located in porous rock or fractures.
• Hot water can be harnessed for energy production.
• Geothermal energy is clean and renewable, to the extent that its source remains for long periods (a magma chamber may take millions of years to cool).
• However, it is a type of energy that can only be harnessed at sites with certain characteristics.
• In Portugal, there is production of high-enthalpy geothermal energy in the Azores archipelago.

Alternative Energy

• Renewable energies are not exhausted and are less polluting; they are the main alternative to fossil fuel energy.
• Developing technologies that increase the efficiency of utilization of these energy sources may be the solution to the energy problems of the future.
• In addition to geothermal, the following sources of renewable energy should be considered: solar, wind, hydro, wave, biomass, and biogas.

Mineral Resources

• Include numerous materials used by humankind that were concentrated, very slowly, by a variety of geological processes.
• Mineral resources can be classified into metallic and non-metallic.
• Metallic:
  • Chemical elements such as iron, copper, silver, or gold are distributed in the crust, forming part of the constitution of various materials in different associations with other elements.
  • “Clarke” is the average concentration of a chemical element in the crust. It is expressed in parts per million (ppm) or grams per tonne (g/ton).
  • A metal deposit is a place where there is a chemical element with a concentration above its clarke.
  • In a mineral deposit, the ore is the usable material that has economic interest. The gangue or barren material is the part that has no economic value associated with the ore.
  • The gangue is usually stored in heaps, which are deposits near the surface of mining operations. The heaps cause visual pollution, increase the risk of landslides, and may contain toxic substances that pollute soil and water.
• Non-metallic:
  • Mineral resources considered non-metallic include minerals such as gravel, sand, and rocks.
  • These materials are abundant, generally do not reach high prices (except for precious stones), and, for these reasons, come from local sources.
• 

Geohazards

Theme 4: Methods for Studying the Interior of the Geosphere

Direct Methods

Observation and Study of Directly Accessible Materials

Several Techniques

• Observation and study of the visible surface
• Exploitation of mineral deposits in mines and excavations
• Drilling
• Magmas and xenoliths
• Tectonic movements and erosion

Observation and Study of the Visible Surface

• Allows more or less complete knowledge of rocks and other materials that outcrop.
• Examples: tunnels, road cuts.
• Restricted to a very shallow part of the Earth.

Exploitation of Mineral Deposits in Mines and Excavations

• Provides direct data to depths ranging between 3 and 4 km.

Drilling

• Involves appropriate drilling equipment.
• Allows removing cores of rock corresponding to millions of years of history.

Ultra-deep Drilling

• > 1500 meters
• Can be conducted in:
  • Continental crust (the deepest: Kola Superdeep Borehole, 12,262 m)
  • Oceanic crust (the deepest: Costa Rica Rift, 3,500 m)
• Issues:
  • Economic and technical (at 300°C, the drill begins to disintegrate)

Volcanoes

• Magmas and xenoliths:
  • Magma comes from depths of around 100 km to 200 km, undergoing changes along the way.
  • On the way to the surface, the magma incorporates fragments of rock from the mantle and crust – the xenoliths or enclaves.

Tectonic Movement and Erosion

• In convergent plate boundaries, the compressive forces are able to create such intense deformations of the lithosphere that rocks from the ocean bottom can be found on top of a mountain – e.g., the Alps.
• Erosion allows the exposure of rocks that were hundreds of millions of years old, thousands of meters deep.

Indirect Methods

• Planetology and Astrogeology
• Geophysical methods (study of the physical properties of the Earth):
  • Seismology
  • Gravimetry
  • Density
  • Geomagnetism
  • Geothermal gradient
  • Geobaric gradient
  • Geoelectricity

Planetology and Astrogeology

• Using the same techniques that are used in studying the Solar System.
• Comparative study of the Solar System and our planet.
• Comparison of meteorites with the structure of our planet:
  • Stony-iron meteorites – mantle
  • Iron meteorites – core

Seismology

• By studying the propagation of seismic waves, geophysicists analyze the trajectories of the waves as they are reflected and refracted when they encounter changes in the properties of the materials they cross.
  • Seismic tomography:
    • 
    • Allows distinguishing inner zones with different temperatures. The hottest zones are identified by the slowing down of seismic waves, while the coldest zones are revealed by the acceleration they cause.

Gravimetry

• All bodies on Earth are subject to a force of attraction called gravity.
• Gravity can be measured by a gravimeter.
• Gravity is:
  • Smaller at the poles (decreases with latitude)
  • Higher in high areas (increases with altitude)
• Gravimeter: a mass of metal suspended by an extended spring, perfectly elastic. The gravitational force acts on the mass, which, in turn, exerts a pull on the spring, stretching it.
  • Formula to calculate gravity:
• 
• Where:
  • M – mass of the Earth
  • R – Earth’s radius
  • m – mass of the body
  • G – gravitational constant determined in the laboratory
• 
• The Earth’s surface is not regular (mountain ranges, plains, etc.).
  • Earth’s equatorial radius is > 21 km than the polar radius.
    • Consequence:
      • The gravitational force varies from area to area.
  • It is necessary to make corrections for various parameters (latitude, altitude, topography).
  • One would expect that the gravitational force would be equal across the entire Earth’s surface.
• Gravity anomalies:
  • Positive: when the density of materials is higher than the material that makes up the surrounding rocks. Example: mineral deposit.
  • Negative: when the density of materials is less than the material that makes up the surrounding rocks. Example: salt diapir.
  • Allows the determination of more or less dense material within the crust.
    • Rock salt – less dense – negative anomaly – smaller acceleration of gravity
    • Ore deposits – denser – positive anomaly – greater acceleration of gravity

Density

• Planet’s average density – 5.5 g/cm³
• Average density of lithospheric rocks – 2.8 g/cm³
• Conclusion: The density of the Earth’s interior is much higher than the density of rocks in the lithosphere.

Geomagnetism

• The Earth has a magnetic field responsible for the natural orientation of the compass – the magnetosphere.
• Lines of the magnetic field pass through the planet and extend from one magnetic pole to the other (north – south).
• This should create a standard geometry (minimum value near the equator to a maximum value near the poles). This does not happen because the heterogeneity of Earth materials disturbs this regularity.
• The magnetic anomalies detected using magnetometers are a good indicator of metal deposits.
• Ferromagnesian minerals (e.g., basalt) record the orientation of the geomagnetic field. They only record the magnetic orientation when temperatures drop to the Curie point (temperature above which a magnetic mineral loses its magnetism).
• Method associated with magmatic rocks.
• Normal polarity: when the rock has the same magnetism as the present magnetic field. The magnetic north coincides with geographic north.
• Reverse polarity: the magnetic north coincides with the geographic south.

Geothermal Gradient

• Main source of heat – radioactive decay of elements found in rocks (uranium, potassium, thorium).
• Internal thermal energy from the Earth’s formation.
• Through measurements and drilling conducted in mines – the temperature increases with depth.
• Geothermal gradient: the amount of temperature variation with depth – temperature increase per km depth.
• In general: every 33 or 34 meters deep, the temperature rises 1°C.
• Geothermal degree: the number of meters it is necessary to descend to increase the temperature by 1°C.
• The variation of the geothermal gradient does not occur uniformly:
  • If this happened, the Earth would reach internal temperatures of thousands of degrees, which would cause the melting of all materials.
  • It is assumed that the variation of the geothermal gradient ( ) decreases with depth.
  • Implies the existence of different types of materials that make up the Earth.
• The dissipation of heat to the surface is called the Heat Flow.
• The amount of heat energy released per unit area and per unit time is:

Geoelectricity

• Geoelectrical methods are considered a good indirect method because they give us information about the Earth’s interior based on the electrical properties of rocks. Thus, by introducing an electric current into the ground, we can determine the conductivity/resistivity of the material, i.e., the ability of the material to allow the current to pass through it. One factor that contributes most to the increase in the conductivity of materials is the presence of water in the strata.

Geobaric Gradient

• There is a constant value, although not as irregular as the geothermal gradient. This inconsistency results from the heterogeneity of the composition of the Earth’s interior, as suggested by the density variations revealed by seismic data.
• When superimposed, the graph of the geobaric gradient and the geothermal gradient do not have anything in common. The only similarity is that pressure and temperature increase with depth.

Theme 5: Volcanism

Volcanology: the science of volcanoes and the phenomena associated with them.

Volcanism: Geological constant manifestation of the dynamics that constitute the central mechanism of evolution of our planet.

• Volcano types:
  • • Volcanism primary
      • Volcano eruption
    • Volcanism secondary
      • Volcanism residual

• Volcanism Primary:

It is characterized by the occurrence of volcanic eruptions in which they are issued outside the Geosphere volcanic materials in solid, liquid and gas – “issued by volcanic apparatus.

• It is divided into:
  • • Volcanism central
      • Volcano: opening the land surface, establishing communication between the interior and exterior of the globe, bringing to the surface large amounts of matter and energy.
        • Volcanic cone: a conical shape in elevation, resulting from the accumulation of material released during one or more eruptions.
        • Vent: channel inside the volcanic apparatus that establishes communication between the magma chamber and the outside.
        • Volcanic crater: the opening of the volcanic cone, funnel-shaped, which sits on top of the vent.
        • Magma chamber, located a few Kms from the surface where magma accumulates.

• 

  Structure of a Volcano:

  • • • Difference between Magma and Lava:
        • Lava: volcanic material has solidified or fluid (degassed magma molten igneous), expelled from the interior of a volcano.
        • Magma: rocky material of deep origin, consists essentially of fused silica at high temperatures and dissolved gases.

• Formation of Power:
  • • • • The evacuation of all or part of the magma chamber becomes unstable volcanic unit (for lack of support from the cone), leading to its reduction.
        • They have a diameter not less than, 1.5 km in diameter.

• Fissure volcanism:
  • • • Eruptions occur along fractures in the Earth’s surface

• Material ejected by volcanoes:
  • • • During volcanic eruptions, are released several product types, including:

Tephra:

• Gases:
  • • • • • Among the gases released during a volcanic eruption, predominantly:
            • Water vapor – “H2O (g)
            • Carbon monoxide – »CO
            • Hydrogen – ‘H2
            • Nitrogen – »N2
            • Hydrochloric acid – ‘HCl
            • Sulphur compounds – ‘SOx

• Burning clouds:
  • • • • • • Made up of fragments of various sizes (mostly gray) involved in high temperature gases that displace the slopes of volcanoes, all before calcining.
        • Lava:
          • Different Classifications:

            • 

              Types of lava under the% SiO2:

• The amount of silica, ie the compound of formula SiO2, is an important parameter for the classification of lava, which allows dividing them into basic lavas, intermediate or acidic.
  • • • • • • Viscosity:

              • 

                The viscosity of lava depends on several factors:

                • Temperature
                • Amount of silica

• Types of lava second viscosity:

• Types of solidification of the lava:
  • • Fluid lava

• Viscous lava

• Types of Eruption
  • Explosive:
    • Highly viscous lavas
    • Violent outbursts
    • Formation of domes or needles
    • Cones and accented by high accumulation of tephra
    • Formation of fiery clouds
  • Effusive:
    • Fluid lava
    • Robes and lava flows
    • Low cone, formed by layers of solidified lava
    • The lava spreads over large areas
  • Mixed:
    • Alternation of phases with effusive explosive phases (mild violence)
    • Cone mixed, resulting from the accumulation of lava interspersed with pyroclastic rocks
    • Explosive eruptions caused by incoming water by volcanic

• Volcanism residual
  • Occur after the volcanic eruptions have ended
  • Manifest themselves in a less spectacular and violent, including the release of gases and / or water at elevated temperatures
    • Residual manifestations of volcanism
      • Fumaroles:
        • Rise to the surface of water at high temperatures that cause emission of water vapor.
        • There is no mixing of these waters with cooler waters underground
        • Depending on the gases that predominate, mixed with water vapor, given different designations:
          • Sulfated (sulfur)
          • Mofet (carbon dioxide)
      • Springs:
        • Groundwater overheated, mixed with groundwater that flow to the surface at temperatures lower than its boiling point
      • Geysers
        • Discontinuous emissions of water and water vapor through cracks

• Economic use of the Volcanism attenuated
  • Direct use as source (spa, spas, greenhouses, food preparation, …)
  • Conversion of heat into electricity
    • In the Azores, the water vapor pressure is captured and taken to a central location, where drives turbines that produce electricity

• Volcanism and Tectonics

  • 

    Distribution of Volcanoes:

• Zones:

• Hot Spots:
• Plumas thermal form (portions of hot material, derived from the mantle, which amount to the lithosphere, resulting in a magma source that feeds a volcano on the surface and is always still the hot spot, which moves the plate where it is located)

• Environmental Hazards:
• Volcanism is one of the factors that influence the Earth’s climate.
• Volcanoes emit into the atmosphere about 110 million tons of CO2 annually
• It is known that:
• Volcanoes emit gases and ash (especially SO2), block sunlight, causing acid rain and can aggravate the greenhouse effect
• Eruptions affect climate over short periods of time, but that may influence long-term changes
• Therefore, environmental damage is inevitable

• Personal risks:
• Over the past 300 years, approximately, 27 volcanic eruptions have caused deaths of an estimated 250 000 people
• It is impossible to avoid an eruption, but you can anticipate when it occurs
• The volcanology has progressed to the point where, today, we know how many are active volcanoes on Earth and which have a higher risk for humans
• How can the human minimize personal risks associated with a volcanic eruption?
• Step 1 – Study the behavior of a volcano:
• Active
• Extinct
• Asleep
• Step 2 – Monitoring:
• Detection of the deformation of the volcanic cone
• Registration of seismic activity
• Temperature variations in the secondary volcanism
• Variations in soil temperature
• Collection and analysis of gases
• Detection of the variation of the gravitational force (gravity anomaly)
• Step 3 – construction of maps of risk areas:
• Construction of maps which can predict the future behavior of the volcano, based on historical data from past eruptions and geological studies of the area around the mountain

• Step 4 – prevention:
• Awareness and education of populations at risk (the inhabitants of the areas included in the risk map
• In short:
• The prediction of volcanic eruptions can minimize personal injury, especially the loss of human lives
• It is important to know whether the volcano is active, dormant or extinct
• Today, through the use of many different technologies, it is possible to predict a volcanic eruption, and we construct maps showing the risk areas.

Theme 6:

• Seismology

Earthquake: movement of the earth’s crust, sharp and short-lived, existing from motions within the Earth.

• Microseconds: low-intensity earthquakes, little violent, that go unnoticed to our senses. Just logged on seismographs.
• Macross: also called earth tremors, high strength and capable of causing numerous changes and disasters. Earthquakes are felt by people.

• Origin of earthquakes:
• Currently seismologists – scientists who are dedicated to the study of earthquakes – these are scientific explanations for natural events

• 

  Inside the earth there are forces acting on the rocks. When these forces exceed the capacity of the rock gives resistance to rupture, forming a fault. The movement along the fault causes earthquakes.

• 

  Types of Faults:

Failover:

• Compressive forces
• Block rocky climbs
• Convergent boundaries

Normal fault:

• Force relaxation
• Block rocky drops ¯
• Divergent boundaries

Fault Slip:

• Force slide
• The farm bloc in others ·
• Borders tangential

• Elastic Rebound Theory:

Enunciated by HF Reid, in 1911, tries to explain the origin of earthquakes. According to this theory, the rocks undergo elastic deformation due to the action of forces. The rocks, as they are being subjected to the action of forces, accumulating power of the forces and will be deformed. However, if the forces fail to act, the rocks recover its original shape, releasing the stored energy (earthquake). If the forces continue to act, may be exceeding the limit of plasticity of the material, fracture, releasing the energy released (earthquake) and an emerging fault. The material, after formation of the failure, recovers the initial form, ie, no longer deformed.

• Types of earthquakes:
• Natural earthquakes:
• Tectonic earthquakes: movement along faults
• Earthquakes collapse: a landslide in a cave or underground to the surface can cause a microsomal
• Volcanic earthquakes: the pressure within a magma chamber can cause earthquakes in volcanic regions
• Artificial earthquakes: those created by man. Always provoke microseconds. Ex: explosions in quarries

• Seismicity in Portugal:

Portugal is located in a relatively unstable (200 km from the border with the African plate), being a country of moderate seismic risk

• Areas of highest seismic risk:
  • Algarve
  • Coastal zone south of Figueira da Foz, including the lower valley of the River Tagus
  • The metropolitan area of ​​Lisbon
  • Azores: zone of the Portuguese territory with great seismic activity due to its location on the boundary of tectonic plates (Eurasian, American and African, forming a triple point with limits of rift and transform faults)

• Consequences of earthquakes

Depending on the intensity and location of the epicenter, earthquakes can:

• Cause changes in topography, soil cracks can open up, the rivers may dry, change your route, or change in water composition
• Cause avalanches, landslides when they occur or snow in mountainous areas
• Tsunamis cause: when the epicenter of an earthquake is located offshore, forming very destructive tidal waves

• Seismic waves:
• Before the main earthquake: aftershocks premonitory or primary
• After the main quake, aftershocks
• Earthquake Principal:

• The epicenter is the area located on the surface vertical to the earthquake focus, which is affected primarily by the effects of earthquakes
  • The hypocenter or focus is the site of origin of an earthquake, located at variable depth (either deep, superficial or intermediate)

• Types of seismic waves
  • Deep waves
    • P waves, primary
      • The particles are moving in the direction of wave propagation (parallel to the direction of propagation)
      • The propagation is carried out through a series of alternating compressions and strains, which changes only the volume of rocks
      • They are the first wave to be recorded by seismographs, and therefore the fastest
      • Propagate through solids, liquids and gases, their spread can be compared to the airwaves
      • Some of the energy transmitted by the P waves can be transmitted to the atmosphere in the form of sound waves, causing noise
      • Known for longitudinal waves of compression, primary or P
    • S waves, secondary
      • The particles are moving perpendicular to the displacement of the wave and therefore are called transverse waves
      • Are slower than P waves, so that come late in relation to P waves at seismograph stations. For this reason are called secondary or S waves
      • Cause only changes in the way of material
      • Only propagate in solid media
  • Surface Waves
    • Love waves, L
      • Love waves involve lateral movement of the particles, resulting in interference between the waves S
      • The particles vibrate horizontally, making the direction of vibration at right angles to the direction of propagation
      • Just moving to the surface in solid media
      • Are the most destructive
    • Rayleigh waves, R
      • R waves cause displacement of soil particles, similar to heavy seas, following an elliptical trajectory in a plane perpendicular to the direction of propagation
      • Waves are slower
      • They move about the Earth’s surface, liquid and solid media

P waves

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S waves

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L waves

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R waves

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• Detection of earthquakes:
  • Seismograph to record the vertical component
  • Seismograph to record the horizontal component (NS; EO)

• Seismogram:

• Measuring earthquakes:
  • Modified Mercalli Scale:

Measures the intensity of the earthquake, based on descriptions of people, these reports will serve to make the letters of isoseismal lines.

Grade I – people do not feel anything

Grade II – the vibrations are felt by people on upper floors of buildings

Grade III – the lamps swaying, the vibration is comparable to that caused by the passage of a small truck

Grade IV – the dishes, cutlery and the windows vibrate, the vibration is comparable to the passage of a 15 ton truck

Phase V – wake up people to sleep, dishes and windows break

Grade VI – the chimneys fall, furniture moves

Grade VII – the walls and buildings fall weak structure

Grade VIII – general alarm; ruin of weak buildings

Grade IX – panic; foundations of buildings affected, burst pipes, cracks in the ground

Grade X – large ruin; rails fold; bridges fall; soil strongly affected

Grade XI – few structures resist; large cracks in the soil

Grade XII – total destruction of the landscape

• Richter scale
  • • Measures the magnitude of an earthquake
    • Usually it is considered that this scale is graduated from 0 to 10, although, properly, one must say that it is an open range (ie, unlimited)
    • Quantitative scale, because it measures the amount of energy released

• Letter of isoseismal lines
  • Corresponds to the set of isoseismal lines, an earthquake on X, covering the region where the earthquake was felt
  • An isoseismal lines, in turn, corresponds to a curved line that delimits regions with the same seismic intensity

• Earthquakes and plate tectonics:
  • Converging areas:
    • Zones of seismicity and largest earthquakes with magnitude greater
    • If convergence is between two continental plates can form mountain ranges
    • If convergence is between oceanic and continental plates, there is the formation of an ocean trench, where subduction occurs oceanic plate (more dense) than the continental plate
  • Divergent Zones
    • Earthquakes associated with zones of mid-ocean ridges
    • Located in the rift parallel faults
    • Earthquakes of magnitude lower than the earthquakes in convergent zones
  • Conservative limits:
    • Earthquakes at transform faults together
    • Horizontal movement of plates in opposite directions
      • In short, these three earthquakes seismic regions because they coincide with the boundaries between several tectonic plates, earthquakes are considered interplate and represent about 95% of the total current earthquakes. The earthquakes that occur within the plate tectonics, earthquakes represent 5% of current and are called intraplate earthquakes.
      • Minimization of seismic risk
        • Prevention:
          • Geological studies of the land: the construction of buildings or infrastructure, should not be performed on active fault
          • Earthquake-resistant buildings: buildings must comply with rules on anti-seismic
          • Training staff: there must be evacuation plans
          • Evacuation plans, should be common knowledge of the population, simulations should be made
          • Education: people should know the emergency plans
        • Behavior to have during an earthquake:
          • Before:
            • Study sites more protection inside and outside the house
            • Blame the adults in the home for a child and explain – you do the procedures
            • Secure cabinets, gas cylinders and materials which may release
            • Have: flashlight, extra batteries, radio, fire extinguisher, first aid kit, canned food and bottled water
          • During:
            • Avoid panic
            • Not to rush to the exits
            • Use the stairs instead of elevator
            • Moving away from sharp objects (eg windows)
            • Protect yourself under a doorway in the corner of a room or under a table or bed
            • If you’re on the road, moving away from tall buildings or isolated
          • Then:
            • Remain calm and avoid panic
            • Not to rush to the exits or stairs
            • Do not light matches or lighters. Use a flashlight
            • Do not turn the electricity or gas
            • Shut off water, gas and electricity as soon as you can
            • Check for fires, if any, call the fire department
            • Check for injuries, if any, call the emergency services
            • Releasing domestic animals
            • Move away from beaches and rivers because of the possibility of tsunamis
            • Calm children and elderly
            • Not circulate through the streets to observe the damage

• Theme 7:
  • Structure and dynamics of the Geosphere
    • Internal discontinuities in the Geosphere:
      • The study of propagation of seismic waves revealed the following conclusions:
        • If the earth were homogeneous, the seismic waves recorded at seismograph stations distant from the epicenter, have arrived in a shorter time than expected
        • The greater the epicentral distance, the greater the difference between the arrival time of seismic waves and the expected time for arrival
        • The greater the epicentral distance, the deeper the dive and seismic waves, the greater its speed, so that we conclude that the speed of seismic waves increases with depth
        • S the waves do not propagate in media stiffness zero (liquid medium), while the P decrease its speed
        • The speed of the waves decreases with increasing density
        • The speed of the waves increases with depth, so that the stiffness with depth, increases more than the density
        • Seismic waves can be skewed during their journey or be absorbed, which reveals the existence of media of different composition, ie, the Earth is heterogeneous
        • There are surfaces of discontinuity revealed by modifying the behavior of the waves

      • 

        

        Existing discontinuities:

• Gutenberg discontinuity: it is located at 2900 km depth separates the lower mantle and outer core. There is the disappearance of S waves and a relaxation of P waves This discontinuity explains the existence of a shadow land
• Lehmann discontinuity: the 5150 km, the Lehmann discontinuity, separates the outer core (liquid) from the inner (solid). There is an increase in shear wave velocities, which shows an increase in stiffness. The inner core is solid due to the immense pressure forces that are felt, the temperature factor is put in the background.

• Gray areas:
  • Area of ​​the surface at a distance between 11,500 and 15,900 km from the epicenter of an earthquake, which are not received by the seismograph stations any P or S waves

• Terrestrial Models:
  • Model chemical (rock composition):
    • Crust:
      • Continental (granite)
      • Oceanic (basalt)
    • Mantle:
      • Superior (peridotite)
      • Bottom (peridotite)
    • Nucleus.
      • External (Fe-Ni liquid)
      • Internal (Fe-Ni solid)
  • Physical Model (stiffness / density):
    • Lithosphere
    • Asthenosphere
    • Mesosphere
    • Endosfera

The Bagacina is a term used only in the Azores