Which of the following are associated with composite volcanoes? I. They result in explosive eruptions. II. They eject pyroclastic materials. III. Pyroclastic materials and ashes accumulate near the vent, forming layers. Select the correct answer using the code given below.
- A.I and II only
- B.II and III only
- C.I and III only
- D.I, II and III
Correct answer
Explanation
The correct answer is D, I, II and III. All three statements describe composite volcanoes, also called stratovolcanoes. Their lava is cooler and more viscous than basalt, so gas cannot escape easily and pressure builds up until the volcano erupts explosively. Along with lava, large amounts of pyroclastic material, that is, fragments of rock, cinders and ash, are thrown out. This material settles in the vicinity of the vent and builds up in alternating layers with lava flows, which is why these volcanoes are tall, steep-sided cones made of strata. Well-known examples are Mount Fuji in Japan, Mount Vesuvius in Italy and Mount St. Helens in the USA. Shield volcanoes such as those of Hawaii are the contrast: runny basalt lava, gentle eruptions and broad, gently sloping cones. Option A is wrong because it leaves out statement III. Option B is wrong because it leaves out statement I. Option C is wrong because it leaves out statement II. Exam tip: composite volcano = viscous lava, explosive, pyroclastics and ash in layers; shield volcano = fluid basalt, gentle slopes.
Practice Questions
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