Describe the processes that form volcanoes.

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Volcanoes space a colorful manifestation of key tectonics processes. Volcanoes are usual along convergent and also divergent plate boundaries. Volcanoes are also found in ~ lithospheric plates away from key boundaries. Where mantle is able to melt, volcanoes may be the result.

Figure 1. World map of active volcanoes.

See if girlfriend can provide a geological explanation for the locations of every the volcanoes in figure 1. What is the Pacific Ring that Fire? Why space the Hawaiian volcanoes situated away from any kind of plate boundaries? What is the cause of the volcanoes follow me the mid-Atlantic ridge?

Volcanoes erupt due to the fact that mantle rock melts. This is the very first stage in developing a volcano. Remember indigenous the thing “Rocks” that mantle may melt if temperature rises, push lowers, or water is added. Be certain to think around how melting occurs in every of the following volcanic settings.

What You’ll discover to Do

Describe assorted volcanic processess at plate boundariesUnderstand the development of hotspots and their common locations

Volcanoes in ~ Plate Boundaries

Figure 2. Hiking in the Cascades

Volcanoes are fun (and difficult) come climb. Climbing in the Cascades arrays in difficulty from a non-technical hike, favor on south Sister, to a technical climb on mountain Baker in i m sorry an ice axe, crampons, and experience are needed.

Convergent bowl Boundaries

Converging plates have the right to be oceanic, continental, or among each. If both are continental they will certainly smash together and kind a hill range. If at the very least one is oceanic, it will subduct. A subducting plate create volcanoes. Locations v converging in i m sorry at least one bowl is oceanic in ~ the boundary have volcanoes.


Melting at convergent plate limits has many causes. The subducting key heats up as it sinks right into the mantle. Also, water is combined in through the sediments lied on top of the subducting plate. Together the sediments subduct, the water rises right into the overlying mantle material and lowers its melting point. Melting in the mantle over the subducting plate leads to volcanoes within an island or continent arc.

Why does melting take place at convergent bowl boundaries? The subducting plate heats up as it sinks right into the mantle. Also, water is mixed in v the sediments lie on peak of the subducting plate. This water lowers the melting point of the mantle material, which increases melting. Volcanoes in ~ convergent plate borders are discovered all follow me the Pacific ocean basin, mainly at the edge of the Pacific, Cocos, and Nazca plates. Trenches note subduction zones, although only the Aleutian Trench and the Java Trench appear on the map in figure 3.

Remember her plate tectonics knowledge. Big earthquakes space extremely usual along convergent bowl boundaries. Due to the fact that the Pacific ocean is rimmed through convergent and also transform boundaries, about 80% of every earthquakes strike around the Pacific Ocean basin (the ring the fire). Why space 75% of the world’s volcanoes found approximately the Pacific basin? that course, this volcanoes are led to by the variety of convergent key boundaries approximately the Pacific.

Figure 3. The Cascade variety is formed by volcanoes produced from subduction the oceanic crust beneath the north American continent.

Pacific Rim

The Pacific Ring that Fire is wherein the bulk of the volcanic activity on the planet occurs. A description of the Pacific Ring the Fire along western north America is a description of the bowl boundaries.

Subduction in ~ the center American Trench creates volcanoes in main America.The mountain Andreas error is a change boundary.Subduction of the Juan de Fuca plate beneath the phibìc American plate creates the Cascade volcanoes.Subduction that the Pacific plate beneath the phibìc American key in the north creates the Aleutian archipelago volcanoes.

This incredible explosive eruption of mount Vesuvius in Italy in A.D. 79 is an instance of a composite volcano that forms as the an outcome of a convergent plate boundary:

Volcanoes in ~ convergent plate borders are uncovered all follow me the Pacific ocean basin, mainly at the edge of the Pacific, Cocos, and Nazca plates. Trenches mark subduction zones.

The Cascades are a chain the volcanoes at a convergent boundary wherein an oceanic key is subducting beneath a continental plate. Especially the volcanoes space the result of subduction that the Juan de Fuca, Gorda, and Explorer plates beneath north America. The volcanoes are located just over where the subducting plate is at the right depth in the mantle because that there come be melting (Figure 3).

The Cascades have been active for 27 million years, although the current peaks space no an ext than 2 million year old. The volcanoes space far enough north and are in a region where storms room common, so countless are covered by glaciers.

The Cascades are presented on this interaction map v photos and also descriptions of each of the volcanoes.

Figure 4. Mt. Baker, Washington.

Divergent key boundaries

Figure 5. A volcano eruption at Surtsey, a little island near Iceland.

At divergent plate boundaries hot mantle absent rises into the space where the key are relocating apart. Together the warm mantle absent convects increase it rises higher in the mantle. The absent is under lower pressure; this lowers the melting temperature of the rock and so that melts. Lava erupts through long cracks in the ground, or fissures.

Why does melting occur at divergent bowl boundaries? hot mantle absent rises where the bowl are moving apart. This releases press on the mantle, i beg your pardon lowers its melting temperature. Lava erupts through lengthy cracks in the ground, or fissures.

Volcanoes erupt at mid-ocean ridges, such as the Mid-Atlantic ridge, wherein seafloor dispersing creates new seafloor in the rift valleys. Where a hotspot is located along the ridge, such as at Iceland, volcanoes prosper high sufficient to develop islands (figure 5).

Mid-Ocean Ridges

Figure 6. Mountain Gahinga in the eastern African Rift valley.

Volcanoes erupt in ~ mid-ocean ridges, such as the Mid-Atlantic ridge, whereby seafloor dispersing creates new seafloor in the rift valleys. Wherein a hotspot is situated along the ridge, such together at Iceland, volcanoes thrive high sufficient to create islands.

Continental Rifting

Eruptions are found at divergent plate boundaries as continents break apart. The volcanoes in number 6 are in the east African Rift in between the African and also Arabian plates. Remember from the chapter Plate Tectonics that Baja California is being broken apart native mainland Mexico as another example of continental rifting.


Melting is typical at convergent plate boundaries.Convergent plate boundaries line the Pacific Ocean container so the volcanic arcs line the region.Melting at divergent plate boundaries is because of pressure release.At mid-ocean ridges seafloor is traction apart and new seafloor is created.

Explore More

Use this source to prize the concerns that follow.

(You deserve to stop watching at 11:02.)

What percent the volcanoes and also earthquakes occur on the Pacific Ring the Fire?How long is the arc that volcanoes along the Pacific Rim?How has actually Augustine collected so high? does it have high or low silica?What type of volcanoes are found along the ring of fire? What wake up to the gas in the magma?what kills so numerous people?What go water execute in hot rock below the surface?What walk carbon-12 indicate?What process brings the sediments and water into the mantle?

Volcanoes Hotspots

Figure 7. Diagram showing a cross ar though the Earth’s lithosphere (in yellow) with magma rising from the mantle (in red)

In geology, the places well-known as hotspots or hot spots are volcanic regions thought to it is in fed by underlying mantle that is anomalously hot compared with the surrounding mantle. They might be on, close to to, or much from tectonic bowl boundaries. Currently, there room two hypotheses that attempt to describe their origins. One argues that they are because of hot mantle feather that rise as heat diapirs from the core–mantle boundary. An alternative hypothesis postulates the it is no high temperature that causes the volcanism, however lithospheric extension that permits the passive increasing of melt native shallow depths. This theory considers the term “hotspot” to be a misnomer, asserting the the mantle resource beneath them is, in fact, no anomalously warm at all. Renowned examples incorporate Hawaii and Yellowstone.


The origins of the principle of hotspots lie in the work of J. Tuzo Wilson, that postulated in 1963 that the Hawaiian Islands an outcome from the slow movement of a tectonic plate throughout a hot region beneath the surface. It was later on postulated that hotspots space fed by small streams of warm mantle rising from the Earth’s core–mantle boundary in a structure referred to as a mantle plume. Whether or not such mantle feather exist is currently the topic of a major controversy in earth science. Estimates for the variety of hotspots postulated to be fed through mantle plumes has actually ranged from around 20 to numerous thousands, over the years, with most geologists considering a few tens come exist. Hawaii, Réunion, Yellowstone, Galápagos, and Iceland are few of the right now most active volcanic regions to i beg your pardon the theory is applied.

Figure 8. Schematic diagram reflecting the physical procedures inside the earth that bring about the generation the magma. Partial melt begins above the blend point.

Most hotspot volcanoes space basaltic (e.g., Hawaii, Tahiti). As a result, castle are less explosive 보다 subduction ar volcanoes, in i beg your pardon water is trapped under the overriding plate. Wherein hotspots occur in continental regions, basaltic magma rises with the continent crust, which melts to type rhyolites. This rhyolites can kind violent eruptions. For example, the Yellowstone Caldera was created by several of the most powerful volcanic explosions in geologic history. However, when the rhyolite is fully erupted, it might be followed by eruptions that basaltic magma increasing through the exact same lithospheric fissures (cracks in the lithosphere). An example of this task is theIlgachuz selection in brothers Columbia, which was created by one early facility series of trachyte and rhyolite eruptions, and late extrusion of a sequence of basaltic lava flows.

The hotspot hypothesis is now very closely linked to the mantle plume hypothesis.

Comparison through island arc volcanoes

Hotspot volcanoes are taken into consideration to have actually a fundamentally different origin native island arc volcanoes. The latter form over subduction zones, at converging plate boundaries. As soon as one oceanic plate meets another, the denser plate is forced downward into a deep s trench. This plate, together it is subducted, release water right into the base of the over-riding plate, and this water mixes with the rock, thus transforming its composition bring about some absent to melt and also rise. The is this the fuels a chain the volcanoes, such together the Aleutian Islands, near Alaska.

Hotspot volcano chains

The joint mantle plume/hotspot hypothesis envisages the feeder frameworks to be fixed loved one to one another, with the continents and seafloor drifting overhead. The hypothesis thus predicts that time-progressive chains of volcanoes are arisen on the surface. Instances are Yellowstone, i m sorry lies in ~ the finish of a chain of extinction calderas, which end up being progressively older to the west. Another example is the Hawaiian archipelago, wherein islands end up being progressively enlarge and an ext deeply eroded to the northwest.

Geologists have tried to use hotspot volcanic chains to track the activity of the Earth’s tectonic plates. This effort has to be vexed through the lack of really long chains, by the truth that countless are no time-progressive (e.g. The Galápagos) and by the fact that hotspots execute not appear to be fixed relative to one an additional (e.g. Hawaii and also Iceland).

Figure 9. Over millions of years, the Pacific Plate has actually moved over the Hawaii hotspot, developing a trail of underwater mountains that stretch throughout the Pacific

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