Composite cones have steep slopes and experience ________ eruptions because they are composed of ________ magma.

Question

BlackTom AI · Accepted Answer

Composite (stratovolcano) cones have steep slopes and experience violent eruptions because they are composed of felsic (or intermediate-to-felsic) magma.

Relevant concepts: magma composition controls viscosity and gas retention; silica-rich magmas (felsic: high SiO2) are viscous and trap volatiles, promoting explosive eruptions. Volcano morphology reflects eruption style: viscous lava solidifies near the vent producing steep slopes and alternating layers of lava and pyroclastic debris form composite cones.

Step-by-step reasoning:
1. Identify the volcano type: composite (stratovolcano) cones are tall, steep-sided mountains built from alternating layers of lava flows, ash, and tephra.
2. Link form to magma behavior: steep slopes occur because lava that is viscous does not travel far from the vent before solidifying, piling up and building steep slopes.
3. Connect viscosity to composition: felsic magmas (rhyolite, dacite, and andesite toward intermediate) have higher silica content than mafic magmas, making them much more viscous.
4. Relate viscosity to explosivity: viscous felsic magmas trap dissolved gases; as pressure decreases, gas expansion leads to fragmentation of magma and violent explosive eruptions (pyroclastic flows, ash columns).
5. Synthesize: composite cones therefore typically erupt violently and are fed by felsic/intermediate magmas.

Why the correct answer is correct: “violent; felsic” directly matches the physical cause—felsic composition yields high viscosity and gas trapping, producing violent eruptions and the steep, layered structure of composite cones (examples: Mount St. Helens, Mount Fuji).

Why the other options are incorrect:
- “violent; mafic”: mafic magma is low in silica, low viscosity, and typically produces effusive (mild) eruptions, not violent ones.
- “mild; felsic”: felsic magmas cause explosive, not mild, eruptions.
- “mild; mafic”: describes shield volcanoes, not composite cones.

Conclusion: The correct choice is violent; felsic, which matches the provided answer.

Composite cones have steep slopes and experience eruptions because they are composed of magma.单项选择题

类似问题

Which of the following structures represents chitin?

In solution, glucose exists in

According to Xenophanes, what should be avoided at a symposium?

What is "kottabos"?

Why are there so many naked figures in vase iconography?

Why was it necessary to have a "hydria" as part of the ceramic vessels used at a symposium?

For what uses other than sympotic were Greek ceramic vessels used?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单

Composite cones have steep slopes and experience ________ eruptions because they are composed of ________ magma.单项选择题