earth science

Stratovolcano

Stratovolcano is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Stratovolcano rather than just read about it. In short: A stratovolcano, also known as a composite volcano, is a typically conical volcano built up by many alternating layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and explosive eruptions.

Key takeaways

Stratovolcano belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Stratovolcano to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Stratovolcano from memory before moving on to harder problems.

Reference excerpt

A stratovolcano, also known as a composite volcano, is a typically conical volcano built up by many alternating layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and explosive eruptions. Some have collapsed summit craters called calderas. The lava flowing from stratovolcanoes typically cools and solidifies before spreading far, due to high viscosity. The magma forming this lava is often felsic, having high to intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less viscous mafic magma. Extensive felsic lava flows are uncommon, but can travel as far as 8 kilometres (5 miles). The term composite volcano is used because strata are usually mixed and uneven instead of neat layers. They are among the most common types of volcanoes; more than 700 stratovolcanoes have erupted lava during the Holocene Epoch (the last 11,700 years), and many older, now extinct, stratovolcanoes erupted lava as far back as Archean times. Stratovolcanoes are typically found in subduction zones but they also occur in other geological settings. Two examples of stratovolcanoes famous for catastrophic eruptions are Krakatoa in Indonesia (which erupted in 1883 claiming 36,000 lives) and Mount Vesuvius in Italy (which erupted in 79 A.D killing an estimated 2,000 people). In modern times, Mount St. Helens (1980) in Washington State, US, and Mount Pinatubo (1991) in the Philippines have erupted catastrophically, but with fewer deaths. The existence of stratovolcanoes on other bodies of the Solar System has not been conclusively demonstrated. Zephyria Tholus is one of two mountains in the Aeolis region of Mars that have been proposed as possible stratovolcanoes.

Distribution

Stratovolcanoes are common at subduction zones, forming chains and clusters along plate tectonic boundaries where an oceanic crust plate is drawn under a continental crust plate (continental arc volcanism, e.g. Cascade Range, Andes, Campania) or another oceanic crust plate (island arc volcanism, e.g. Japan, Philippines, Aleutian Islands). Stratovolcanoes also occur in some other geological settings, for example as a result of intraplate volcanism on oceanic islands far from plate boundaries. Examples are Teide in the Canary Islands, and Pico do Fogo in Cape Verde. Stratovolcanoes have formed in continental rifts. Examples in the East African Rift are Ol Doinyo Lengai in Tanzania, and Longonot in Kenya.

Formation Subduction zone volcanoes form when hydrous minerals are pulled down into the mantle on the slab. These hydrous minerals, such as chlorite and serpentine, release their water into the mantle which decreases its melting point by 60 to 100 °C (110 to 180 °F). The release of water from hydrated minerals is termed "dewatering", and occurs at specific pressures and temperatures for each mineral, as the plate descends to greater depths. This allows the mantle to partially melt and generate magma. This is called flux melting. The magma then rises through the crust, incorporating silica-rich crustal rock, leading to a final intermediate composition. When the magma nears the top surface, it pools in a magma chamber within the crust below the stratovolcano. The processes that trigger the final eruption remain a question for further research. Possible mechanisms include:

Magma differentiation, in which the lightest, most silica-rich magma and volatiles such as water, halogens, and sulfur dioxide accumulate in the uppermost part of the magma chamber. This can dramatically increase pressures. Fractional crystallization of the magma. When anhydrous minerals such as feldspar crystallize out of the magma, this concentrates volatiles in the remaining liquid, which can lead to a second boiling that causes a gas phase (carbon dioxide or water) to separate from the liquid magma and raise magma chamber pressures. Injection of fresh magma into the magma chamber, which mixes and heats the cooler magma already present. This could force volatiles out of solution and lower the density of the cooler magma, both of which increase pressure. There is considerable evidence for magma mixing just before many eruptions, including magnesium-rich olivine crystals in freshly erupted silicic lava that show no reaction rim. This is possible only if the lava erupted immediately after mixing since olivine rapidly reacts with silicic magma to form a rim of pyroxene. Progressive melting of the surrounding country rock. These internal triggers may be modified by external triggers such as sector collapse, earthquakes, or interactions with groundwater. Some of these triggers operate only under limited conditions. For example, sector collapse (where part of the flank of a volcano collapses in a massive landslide) can only trigger the eruption of a very shallow magma chamber. Magma differentiation and thermal expansion also are ineffective as triggers for eruptions from deep magma chambers.

Hazards

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Stratovolcano

Start with the simplest possible case. Write down what Stratovolcano claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Stratovolcano before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Stratovolcano ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Stratovolcano

In research: Stratovolcano appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Stratovolcano in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Stratovolcano is common in secondary-school and first-year university syllabi. It links to neighbouring topics Stratovolcanoes, Volcanic landforms, so understanding it makes those chapters shorter.
In everyday life: Look for Stratovolcano outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Stratovolcano in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Stratovolcano means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Stratovolcano out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Stratovolcano in simple terms?

Why does Stratovolcano matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Stratovolcano?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Stratovolcano.