XII-3. Natural Disasters (Volcanoes, Earthquakes)

Warm-Up & Vocabulary

Key Vocabulary

• Inference (n.): A logical conclusion drawn from hints, facts, or context clues in a text rather than a direct statement.
• Seismic (adj.): Relating to earthquakes or other vibrations of the earth and its crust.
• Magma Chamber (n.): A large pool of liquid rock beneath the surface of the Earth that feeds a volcano.
• Tectonic Plates (n.): Massive, irregularly shaped slabs of solid rock that compose the Earth’s lithosphere.
• Viscosity (n.): A fluid’s resistance to flow; high viscosity magma flows slowly and often traps gases, leading to explosive volcanic eruptions.

Vocabulary Quiz: Matching

Making Simple Inferences in TOEFL iBT Reading

Inference questions on the TOEFL iBT test your ability to comprehend implied meaning. The passage will not state the answer explicitly; instead, you must connect facts presented in the text to identify what must logically be true.

Recognizing Inference Question Stems

• “Which of the following can be inferred from paragraph X about…?”
• “The author implies that…?”
• “Which of the following is suggested by the passage regarding…?”

Core Strategy: The “Must Be True” Rule

• Use Strict Textual Logic: A valid inference must be supported directly by facts in the passage. Do not use outside knowledge or make wild assumptions.
• Avoid Extreme Statements: Options containing extreme words like always, never, completely, or impossible are usually incorrect unless explicitly backed by the text.
• Identify Clue Words: Look for cause-and-effect indicators (“as a result”, “due to”), conditional structures (“if… then”), or comparative phrasing (“unlike shield volcanoes…”).

Worked Example

Passage Snippet:

“Unlike composite volcanoes, which produce explosive eruptions due to high-viscosity magma trapping pressurized gases, shield volcanoes emit low-viscosity basaltic lava that flows easily across vast distances.”

• Direct Fact: Composite volcanoes trap gas due to thick magma $\rightarrow$ explosive. Shield volcanoes have runny lava $\rightarrow$ non-explosive/flowing.
• Valid Inference: Shield volcanoes are generally less explosive than composite volcanoes because their low-viscosity lava allows trapped gases to escape easily.

Skill Practice

Practice Quiz 1: Fill in the Blank

Practice Quiz 2: True or False

Read the passage snippet and decide whether the inference statement is True or False.

“Seismologists noted that during the major fault rupture, buildings built on loose, water-saturated sediment suffered catastrophic structural failure, whereas nearby structures anchored directly to bedrock remained standing with minor cosmetic damage.”

Practice Quiz 3: Multiple Choice

“Prior to the 1980 eruption of Mount St. Helens, the north flank of the mountain began bulging outward at a rate of up to five feet per day. Authorities established an evacuation zone around the volcano despite heavy protests from local logging companies whose business was halted.”