File Name: plate tectonics and volcanoes .zip
Thursday, October 30, Acids can corrode some natural materials. Acids have pH levels lower than 7. Also called a scoria cone. Also called an extensional boundary.
Plate tectonics is the fundamental mechanism that drives geological processes in the geosphere. Plate tectonic theory is based on an understanding of the Earth's internal structure, the different types of tectonic plates and plate boundaries, and the driving forces of plate movements.
The occurrence of earthquakes and volcanoes, the distribution of different rock types, and the Rock Cycle, as well as the processes of mountain building, continental rifting and seafloor spreading, can be concisely explained by plate tectonic processes.
The Earth is an irregular sphere, with a radius that varies between 6, and 6, kilometres. This solid sphere is chemically divided into layers that become less dense from the centre towards the surface. Three main layers are recognised: the core which comprises an Inner Core and an Outer Core , the mantle , and the crust. Each layer has a distinctive chemical composition, and a different density Figure 1. Scientists infer that the dense core is primarily composed of the heavy elements iron and nickel.
The outer core is made of molten iron, which produces the Earth's magnetic field. Surrounding the core is the less-dense mantle, which extends to a depth of about 2, kilometres.
The mantle is rich in iron- and magnesium-bearing silicate minerals. The outer layer of the Earth is termed the crust, which is divided into oceanic crust and continental crust.
Overall, continental crust is richer in the element silica, and is less dense, than oceanic crust. The crust and upper part of the mantle of the Earth is further subdivided into the lithosphere and the asthenosphere Figure 2.
The slow movement of the lithospheric plates over the mobile asthenosphere is known as plate tectonics, a process that maintains the surface of the Earth in a dynamic and active state. Plate tectonics is driven by the internal heat energy of the Earth. This comprises the heat left over from the initial formation of the Earth, combined with heat from the decay of radioactive minerals contained in the rocks.
Heat from the Earth's lower mantle rises as plumes towards the upper mantle where cooling occurs. The plumes spread out, then sink back into the interior Figure 3. This process is known as mantle convection. These convection currents propel the motion of plates.
Although heat drives mantle convection and the motion of plates, the mantle is mostly solid. The rock forming the mantle, however, behaves in a semi-plastic manner, which enables the slow transfer of materials. There are three types of plate boundary: convergent , divergent , and transform plate boundaries.
Figure 4a: Generalised structure of a divergent plate boundary. Figure 4a : occur where two lithospheric plates move away from each other, driven by magma rising from deep within the mantle. Volcanic activity at a divergent plate boundary creates new lithosphere along what is known as a spreading ridge. Figure 4b: Generalised structure of a convergent plate boundary. Figure 4b : occur where two lithospheric plates move towards each other, with one plate overriding the other.
The overridden plate is driven back into the mantle, and is subsequently destroyed along what is known as a subduction zone. During this process, earthquakes and volcanic activity are generated in the overriding plate.
Figure 4c: Generalised structure of a transform plate boundary. Figure 4c : occur where two lithospheric plates slide laterally past each other. Earthquakes are generated along this type of plate boundary. Importantly, lithosphere is preserved along transform boundaries, it is not created or destroyed as it is at divergent and convergent plate boundaries.
Plate tectonics is a process that maintains the surface of the Earth in a dynamic and active state. Consequently, it drives such processes as:. Within regions of continuous continental crust, the process of mantle upwelling leads to thinning of the crust and to the development of rift valleys. Figure 5: Seismic waves generated by movement along a fault deep underground. Figure 6: Creation of a volcanic mountain chain along a convergent plate boundary.
Figure 7: Development of a back-arc rift zone behind a chain of volcanoes adjacent to a convergent plate boundary. Magma is derived from deep within the Earth by partial melting of the upper mantle or lower crust.
It is composed of a high temperature mixture of silicate material magmatic liquid , water, and dissolved gases. Magma may also contain crystals that formed during cooling of the magma, and rock fragments incorporated into the magma during its ascent towards the Earth's surface.
Magmatism is the process by which molten rock magma rises to the upper crust where it may:. Solid mantle material rises close to the Earth's surface at divergent plate boundaries Figure 8. This process is accompanied by a decrease of pressure, which lowers the melting temperature of the mantle material. Thus, when the solid mantle reaches a certain level, it begins to partially melt to form a magmatic liquid.
Buoyancy causes the magmatic liquid to rise towards the Earth's surface, away from the zone of melting, leaving behind unmelted solid material. Partial melting, caused by the reduction in pressure associated with the upward movement of mantle, is termed decompression melting. Decompression melting is also responsible for the production of magma at hotspots Figure 8. A hotspot is a location where an active convection system occurs within the mantle.
At these locations, the solid mantle materials are hotter and less dense, and are moving upwards towards the crust in plumes. At convergent plate boundaries, the subducting plate is heated as it descends, releasing hydrous fluids into the plate above Figure 8. The injection of these fluids into the overlying lithospheric mantle causes a lowering of the melting point of the mantle materials, which partially melt to form magma. These magmas rise to the surface through the crust, feeding the volcanoes that occur in both island arc and continental margin arc settings.
Magma erupted from a volcano is generally a mixture of three main components, crystals, magmatic liquid, and dissolved gases mostly water vapour. Different types of volcanoes occurring in contrasting plate tectonic settings will exhibit varying degrees of explosivity depending upon the composition of the erupting magma, in particular the dissolved gas content.
When a magma is erupted at the surface, any dissolved gas comes out of solution and is released in the form of gas bubbles. Around the world, a complete spectrum of magma compositions can be found. These range from magmas rich in magnesium and iron aluminium silicate minerals basalt , to those rich in sodium, potassium, and calcium aluminium silicate minerals rhyolite , with a range of intermediate magmas occurring in between e.
The magma in basaltic volcanoes is relatively hot, and flows easily. This allows any gas bubbles to escape, resulting in largely non-explosive eruptions. In contrast, the magma in rhyolitic volcanoes is relatively cooler and more viscous. Any gas bubbles in the rhyolitic magma have great difficulty escaping, and are explosively released, shattering the magma.
Thus, rhyolitic volcanoes are more explosive than basaltic volcanoes, producing greater quantities of ash. Three common types of volcanoes that occur in different tectonic settings are shield volcanoes, stratovolcanoes , and caldera volcanoes. Most basaltic eruptions in intraplate or mid-ocean spreading centre settings form low surface slope shield volcanoes.
Typically, lava fountains from the vent in these eruptions Figure Large volumes of low viscosity basaltic magma pour out as rivers of lava. This style of eruption is characteristic of Hawaiian-type volcanoes. Volcanoes associated with continental margin arc or island arc tectonic settings are dominantly andesitic or rhyolitic in composition.
These volcanoes typically form stratovolcanoes composite volcanoes , and the eruption style is generally more explosive than Hawaiian-type volcanoes. A typical stratovolcano has a steep cone shape, made up of alternating layers of ash and lava Figure Depending upon the amount of dissolved gas contained in the erupting magma, the eruptions at stratovolcanoes may vary from minimally explosive Strombolian-type to highly explosive Plinian-type.
The greater the dissolved gas content, the more explosive an eruption will be, and the larger the volume of erupted volcanic ash. Rhyolitic volcanoes in convergent boundary tectonic settings may form caldera volcanoes. Caldera volcanoes are ones in which the top part of the volcano has been explosively destroyed following collapse into an underlying drained magma chamber Figure Caldera volcanoes are the result of very violent eruptions.
The volcanic rocks that occur in Hong Kong are predominantly of rhyolitic composition, consisting mainly of ash. These rocks were formed by violent eruptions of ash from caldera-type volcanoes.
Ash clouds from caldera-type volcanoes are commonly so large, that they collapse under gravity and flow over the landscape like a fiery fluid. Hazards created by volcanoes can be divided into those that are produced directly from volcanic activity primary hazards , and those that are produced indirectly from volcanic activity secondary hazards Figure Primary hazards include: lava flows, pyroclastic flows, ash-falls, and gas emissions. Secondary hazards include: lahars mud flows , floods, fires, and tsunami large sea waves.
Earthquakes are associated with all types of plate boundary. They result from the sudden release of energy that occurs when the stress that builds up between two adjacent, moving tectonic plates finally overcomes the friction that holds the two plates together Figure At transform plate boundaries , such as the San Andreas Fault in California, lateral displacement between two adjacent plates may occur in sudden catastrophic movements that leads to splitting of the Earth's crust at the surface.
These ruptures in rock are known as faults. At divergent or convergent plate boundaries , the movement between the tectonic plates may occur at any depth below the Earth's surface.
However, some earthquakes that occur in subduction zones may be associated with faults that reach the surface. In some cases, these can result in catastrophic vertical movements of the ground and the generation of tsunamis, such as the one that occurred following the December Indian Ocean earthquake.
Home 1. Minerals and Rocks - Geological Building Blocks 2. Surveying the Landscape - Introduction to Geological Mapping 4. History of Geological Studies of Hong Kong 6. Geological History and Hong Kong Rocks 7.
Structural Geology 8. Plate Tectonics - Formidable Forces Plate tectonics is the fundamental mechanism that drives geological processes in the geosphere.
German meteorologist Alfred Wegener is often credited as the first to develop a theory of plate tectonics, in the form of continental drift. Scientists discovered later that Pangea fragmented early in the Jurassic Period. The heat source is thought to be the decay of radioactive elements. How this convection propels the plates is poorly understood. Some geologists argue that upwelling magma at spreading centres pushes the plates, whereas others argue that the weight of a portion of a subducting plate one that is forced beneath another may pull the rest of the plate along. The Ring of Fire is a long horseshoe-shaped earthquake-prone belt of volcanoes and tectonic plate boundaries that fringes the Pacific Ocean basin.
Magma I. Composite stratovolcano cone A volcano that consists of alternating layers of lava and ash. High viscosity magma. Most violent I.
Thus far volcanoes have been discussed in terms of the kinds of volcanic mountains they form, the materials they produce, and the style of eruption they have. All of these characteristics can be tied together into a big picture by considering the plate tectonic settings in which magma forms Figure The vast majority of volcanoes are present along plate tectonic boundaries. At an ocean spreading ridge centre of Figure
Countries located along plate boundaries, such as the Eastern Caribbean islands, Japan, Chile and the USA California are likely to experience earthquakes.
Students model Earth's tectonic plate movement and explore the relationship between these movements and different types of volcanoes. Much of the content is the same. The full original lesson can be found here. Show students pieces of a jigsaw puzzle or have them think of what puzzle pieces look like.
Volcanism or volcanicity is the phenomenon of eruption of molten rock magma onto the surface of the Earth or a solid-surface planet or moon, where lava , pyroclastics and volcanic gases erupt through a break in the surface called a vent. Magma from the mantle or lower crust rises through its crust towards the surface. If magma reaches the surface, its behavior depends on the viscosity of the molten constituent rock. Viscous thick magma produces volcanoes characterised by explosive eruptions , while non-viscous runny magma produce volcanoes characterised by effusive eruptions pouring large amounts of lava onto the surface. In some cases, rising magma can cool and solidify without reaching the surface. Instead, the cooled and solidified igneous mass crystallises within the crust to form an igneous intrusion. As magma cools the chemicals in the crystals formed are effectively removed from the main mix of the magma by a process known as fractional crystallization , so the chemical content of the remaining magma evolves as it solidifies slowly.
This is a lesson where learners explore plate movement and the relationship between plate tectonics and volcanoes. The lesson models scientific inquiry using the 5E instructional model and includes teacher notes, prerequisite concepts, common misconceptions, student journal and reading. This is lesson five in the Astro-Venture Geology Training Unit that was developed to increase students' awareness of and interest in astrobiology and the many career opportunities that utilize science, math and technology skills. The lessons are designed for educators to use with the Astro-Venture multimedia modules. First Name:.
Plate tectonics is the fundamental mechanism that drives geological processes in the geosphere. Plate tectonic theory is based on an understanding of the Earth's internal structure, the different types of tectonic plates and plate boundaries, and the driving forces of plate movements. The occurrence of earthquakes and volcanoes, the distribution of different rock types, and the Rock Cycle, as well as the processes of mountain building, continental rifting and seafloor spreading, can be concisely explained by plate tectonic processes.
Students are able to explain the relationships between earthquakes, volcanoes, and plate boundaries in the western United States and Alaska.