Geologic Processes on the Earth's Surface
Geologic Processes on the Earth's Surface
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Weathering, erosion, mass-wasting, and depositional processes occur at or near the Earth's surface and alter the landscape, influencing surface and subsurface topography and landform development.
Weathering
Weathering
Weathering is the gradual destruction of rock at the surface. Weathering can be caused by physical processes (known as mechanical weathering) or by chemical activity (called chemical weathering). Biological activity can also cause weathering, which can be mechanical, chemical, or both. It can begin long before rocks are exposed on the surface. This is true in most areas of the earth's surface where rocky outcrops (bedrock) are not visible. Furthermore, weathering and erosion can occur concurrently, perhaps most visibly in situations such as rivers in flood or waves crashing on a beach.
Effects of Physical and Chemical Conditions on Weathering
Effects of Physical and Chemical Conditions on Weathering
Particle size effects - The greater the surface area in a uniform volume of sediment, the smaller the particle.
Oxidation-Reduction effects - The availability of oxygen governs mineral stability and solubility; metal oxides precipitate in oxidizing conditions; and reducing environments are acidic.
Acid-Base effects - In basic water, silica dissolves; in acidic water, it precipitates; In acidic water, calcite dissolves and precipitates; in basic water, it dissolves and precipitates.
Color - The majority of color in rocks and sediments is caused by iron oxidation states. Oxygenated sediments are typically brightly colored - red, orange, yellow, and brown. Reduced (acidic) environments are typically green, blue-gray, or black in color.
Erosion
Erosion
The mechanical processes of wearing or grinding away materials on a landscape by the action of wind, flowing water, or glacial ice are referred to as erosion. Erosion also includes the downward movement of materials under the influence of gravity, which is referred to as mass wasting. Erosion rates differ greatly between regions due to climate factors, weather patterns, and bedrock conditions.
As subsurface weathering continues, spheroidal rounded boulders of unaltered bedrock (granite in this case) are surrounded by deeply weathered rock (saprolite).
Weathered material erodes faster, leaving piles of boulders in some places that cover the landscape. This spheroidal boulder-covered landscape can be found in California's Joshua Tree National Park.
Erosion occurs both on land and on the seafloor.
A mile of rock has been eroded away by the Colorado River where it crosses the Kaibab Plateau in the Grand Canyon.
Depicts the eroded roots of a volcanic arc region in Idaho's City of Rocks National Preserve.
In many parts of the world, human activity has become a dominant force of erosion. Mining operations, highway construction, and urban construction have moved more materials in some places than natural erosion has moved in millions of years.
Mass Wasting
Mass Wasting
Mass wasting is a rapid form of erosion that is primarily caused by gravity in conjunction with other erosional agents. Mass wasting occurs quickly and can result in either small or large-scale changes to the landscape, depending on the type of event — rock falls, landslides, debris/mud flows, slumps, and creep.
Landslides are extremely dangerous. Estimates vary, but it is currently believed that landslides kill thousands to tens of thousands of people each year, most often in conjunction with storms in mountainous terrain and areas with poor land-use planning and building codes. Landslides caused by large volcanic eruptions can cause even more damage.
The Blackhawk Landslide in California is one of the largest known landslides in North America. It is situated in the Lucerne Valley (east of LA). The Blackhawk slide is about 5 miles long, 2 miles wide, and 30-100 feet thick. Because of the dry climate, the landslide occurred in prehistoric times but has been well preserved. It serves as a sobering reminder of the dangers of living in landslide-prone areas.
Sedimentation
Sedimentation
The deposition of a solid material from a state of suspension or solution in a fluid is known as sedimentation (usually air or water). It also includes glacial ice deposits and materials collected solely by gravity, such as talus deposits or rock debris accumulations at cliff bases.
It is easy to argue that humans have become a major, if not the primary, force of erosion on the planet. Cities, highways, agriculture, dams, levees, and massive mining operations for metals, building materials, coal, and other resources are now changing the planet's surface faster than all-natural landscape-changing forces combined. That is, for the most part, in most years. Some of that construction is done to try to prevent natural disasters from destroying developments, with varying degrees of success.
Geologic Processes within the Earth
Geologic Processes within the Earth
Geological processes are phenomena that take place across geological timescales ranging from millions of years to hundreds of meters to thousands of kilometers.
Natural disasters are caused by a range of phenomena that occur on and within the Earth.
Melting is responsible for the formation of magmas, which result in volcanism.
Deformation is the cause of earthquakes, volcanism, landslides, and subsidence.
Isostatic adjustment caused by buoyancy causes earthquakes, landslides, and subsidence.
Weathering is the cause of landslides and subsidence.
Erosion is responsible for landslides, subsidence, and flooding.
Hurricanes, tornadoes, and floods are all caused by atmospheric circulation.
Why is the core layer hot?
Why is the core layer hot?
The Earth is divided into three layers: the crust (the outermost layer), the mantle (the middle layer), and the core (the innermost layer).
The crust is made up of minerals and solid rocks. It contains all known life forms on Earth.
The mantle is largely made up of solid rocks and minerals, although it also contains pockets of semi-solid magma.
The core is constructed of dense metals such as nickel and iron. It is also regarded as the Earth's core and the hottest region.
Mantle Convection
Mantle Convection
Mantle convection is the movement of the mantle as heat is transferred from the core to the crust. The temperature of the mantle fluctuates depending on whether it is close to the crust or close to the core's boundary. The decay of radioactive elements and the heat of the liquid outer core, which solidifies towards the inner core, are the primary sources to the core's heat.
Earth's Heat Budget
Earth's Heat Budget
Earth’s heat budget drives most of the geological processes on Earth. This measures the flow of thermal energy coming from the core, passing through the mantle, and up to the atmosphere, which is mainly due to the mantle convection. This, however, is counteracted by the solar radiation.
Folding and Faulting of Rocks
Folding and Faulting of Rocks
Rocks that were originally deposited in horizontal layers can subsequently deform by tectonic forces into folds and faults. Folds constitute the twists and bends in rocks. Faults are planes of detachment resulting when rocks on either side of the displacement slip past one another.
Types of Folds
Types of Folds
Anticlines are layered rocks folded into arches
Synclines are layered rock folded into throughs
Monoclines only have one limb
Types of Faults
Types of Faults
Normal Fault occurs when when tensional force slips the hanging wall downward relative to the footwall
Reverse Fault occurs when compressional forces push the hanging wall upward relative to the footwall
Strike-slip Fault occurs when shear forces move past one block horizontally
The Internal Structure of the Earth
The Internal Structure of the Earth
Earth's interior is generally divided into three major layers: the crust, the mantle, and the core
Crust
Crust
The Earth's lightest, most buoyant rock layer made of solid rocks and minerals.
Continental Crust is formed at convergent plate boundaries, where tectonic plates crash into each other
Oceanic Crust is constantly formed at mid-ocean ridges, where tectonic plates are tearing apart from each other.
Mantle
Mantle
It is the viscous layer that makes up more than half of Earth's
volume. The mantle is about 2,900 kilometers (1,802
miles) thick, and makes up a whopping 84% of Earth’s total volume.
Upper Mantle
Upper Mantle
The upper mantle extends from the crust to a depth of about 410 kilometers (255 miles). The upper mantle is mostly solid, but its more malleable regions contribute to tectonic activity.
Two parts of the upper mantle are often recognized as distinct regions in Earth’s interior: the lithosphere and the asthenosphere.
Lithosphere is both the coolest and the most rigid of Earth’s layers
Asthenosphere is the denser, weaker layer beneath the lithospheric mantle
Core
Core
Earth’s core is the very hot, very dense center of our planet. It is is found about 2,900 kilometers (1,802 miles) below Earth’s surface, and has a radius of about 3,485 kilometers (2,165 miles).
Earth’s core is the furnace of the geothermal gradient. The geothermal gradient measures the increase of heat and pressure in Earth’s interior. The primary contributors to heat in the core are the decay of radioactive elements, leftover heat from planetary formation, and heat released as the liquid outer core solidifies near its boundary with the inner core.
Outer Core
Outer Core
The outer core, about 2,200 kilometers (1,367 miles) thick, is mostly composed of liquid iron and nickel.
Inner Core
Inner Core
The inner core is a hot, dense ball of (mostly) iron. It has a radius of about 1,220 kilometers (758 miles).
Continental Drift
Continental Drift
The continental drift hypothesis was developed in the early part of the 20th century, mostly by Alfred Wegener. It describes one of the earliest ways geologists thought continents moved over time.
Continental Drift
Continental Drift
According to Alfred Wegener, continents move around on Earth’s surface and that they were once joined together as a single supercontinent. He proposed that the continents were once united into a single supercontinent named Pangaea, meaning all earth in ancient Greek. He also suggested that Pangaea broke up long ago and that the continents then moved to their current positions. He called his hypothesis continental drift.
Wegener describe Pangaea and continental drift. For example, fossils of the ancient reptile Mesosaurus are only found in southern Africa and South America. Mesosaurus, a freshwater reptile only one meter (3.3 feet) long, could not have swum the Atlantic Ocean. The presence of Mesosaurus suggests a single habitat with many lakes and rivers.
Seafloor Spreading
Seafloor Spreading
Sea floor spreading is the geologic phenomena of new sea floor being created through mid-ocean ridges.
Seafloor Spreading
Seafloor Spreading
It occurs at divergent plate boundaries. As tectonic plates slowly move away from each other, heat from the mantle’s convection currents makes the crust more plastic and less dense. The less-dense material rises, often forming a mountain or elevated area of the seafloor. Eventually, the crust cracks. Hot magma fueled by mantle convection bubbles up to fill these fractures and spills onto the crust. This bubbled-up magma is cooled by frigid seawater to form igneous rock. This rock (basalt) becomes a new part of Earth’s crust.
Seafloor spreading disproves an early part of the theory of continental drift. Supporters of continental drift originally theorized that the continents moved (drifted) through unmoving oceans. Seafloor spreading proves that the ocean itself is a site of tectonic activity.
Continental Drift & Seafloor Spreading
Continental Drift & Seafloor Spreading
Similar to Wegener’s theory that continents do in fact move, Harry Hess’ seafloor spreading contradicted Wegener’s continental drift in that it involved the ocean sea floor moving as it expanded—instead of continents ploughing through the sea.
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