Question 77·Medium·Rhetorical Synthesis
While researching a topic, a student has taken the following notes:
- Mauna Loa (Hawaii) is a shield volcano with broad, gently sloping sides.
- Its low-viscosity basaltic lava allows gases to escape easily, so eruptions are generally non-explosive.
- Mount St. Helens (Washington) is a stratovolcano with steep sides.
- Its thicker andesitic–rhyolitic lava traps gases, leading to highly explosive eruptions.
- Shield volcanoes and stratovolcanoes thus differ markedly in eruption style.
The student wants to highlight the difference in eruption style between the two volcano types. Which choice most effectively uses relevant information from the notes to accomplish this goal?
For rhetorical synthesis questions based on notes, first underline the stated goal in the prompt (here, “difference in eruption style”). Then, quickly scan the notes to find the bullets that relate directly to that goal and ignore other details. Next, eliminate any answer choices that focus on the wrong aspect (such as shape, location, or structure) or add information not clearly supported by the notes. Finally, choose the option that uses the most relevant notes and directly achieves the stated purpose in a single clear sentence.
Hints
Restate the task in your own words
Ask yourself: What exactly does the question say the student wants to highlight—shape, location, or how they erupt?
Match the goal to the notes
Look for the bullets in the notes that talk about what the eruptions are like (for example, whether they are gentle or explosive, and why).
Scan answer choices for that specific contrast
Eliminate any option that doesn’t clearly describe how each type of volcano erupts or doesn’t set up a direct comparison between the two types.
Step-by-step Explanation
Identify the student’s goal
The question states that the student wants to highlight the difference in eruption style between shield volcanoes and stratovolcanoes. So the correct answer must clearly contrast how they erupt (for example, gentle vs. explosive), not just where they are or what they look like.
Find relevant information in the notes
Look back at the notes and underline anything about eruptions:
- Mauna Loa: "Its low-viscosity basaltic lava allows gases to escape easily, so eruptions are generally non-explosive."
- Mount St. Helens: "Its thicker andesitic–rhyolitic lava traps gases, leading to highly explosive eruptions."
- Summary note: "Shield volcanoes and stratovolcanoes thus differ markedly in eruption style."
These points are the key facts the correct choice should use.
Eliminate choices that don’t focus on eruption style
Check each option and ask: Does this describe and contrast how they erupt?
- A talks about broad vs. steep sides (shape), not eruption style.
- C mentions that they are in the United States and different categories, not how they erupt.
- D talks about layers of ash and lava vs. basaltic flows (structure and composition), but not eruption style.
Those three choices fail to highlight the eruption style difference the prompt asks for, so they can be eliminated.
Confirm the remaining choice matches the notes and goal
The remaining option directly contrasts gentle vs. explosive eruptions and correctly explains that low-viscosity basaltic lava lets gas escape (gentle eruptions) while thicker andesitic or rhyolitic lava traps gas (explosive eruptions), which is exactly what the notes say and exactly the contrast in eruption style the student wants to highlight. Therefore, the correct answer is:
Unlike shield volcanoes such as Mauna Loa, whose low-viscosity basaltic lava produces relatively gentle eruptions, stratovolcanoes like Mount St. Helens erupt explosively because their thicker andesitic or rhyolitic lava traps more gas.