Examkin

Question

Difficulty: MediumIdentifying Points of Disagreement

### Hotspot Volcanism

Hotspot volcanism refers to volcanic activity that occurs away from tectonic plate boundaries, such as the Hawaiian Islands. Two scientists discuss the mechanism responsible for this phenomenon.

Scientist 1
Hotspot volcanism is driven by deep mantle plumes—narrow columns of hot, solid mantle rock that rise from the core-mantle boundary (approximately 2,900 km2,900\text{ km} deep). Because these plumes originate from deep within the Earth, their locations remain stationary relative to the moving lithospheric plates above. As a tectonic plate slides over a stationary plume, a linear chain of volcanoes is formed, with volcano age increasing progressively with distance from the active hotspot. The high temperature of the plume causes localized melting of the lithosphere.

Scientist 2
Hotspot volcanism is a passive process caused by cracks and tension in the tectonic plates themselves. Stress within a plate causes the lithosphere to stretch and fracture. This fracturing allows magma from the shallow upper mantle (less than 200 km200\text{ km} deep) to escape to the surface. These hotspots are not stationary; rather, their locations migrate along with the stress patterns of the plates. The linear chains of volcanoes result from the propagation of lithospheric cracks over time, meaning the age progression is determined by crack propagation velocity, not plate velocity.

Based on the passage, match each point of disagreement between Scientist 1 and Scientist 2 to the correct pair of contrasting viewpoints.

  • The depth of origin for hotspot magmaDeep core-mantle boundary (2,900 km2,900\text{ km}) vs. shallow upper mantle (less than 200 km200\text{ km})
  • The mobility of the hotspot sourceStationary vs. migrating with plate stress patterns
  • The factor determining the rate of age progression in a volcanic chainTectonic plate velocity vs. lithospheric crack propagation velocity

Answer

The depth of origin matches deep core-mantle boundary vs. shallow upper mantle; the mobility of the hotspot source matches stationary vs. migrating with plate stress patterns; and the factor determining the rate of age progression matches tectonic plate velocity vs. lithospheric crack propagation velocity.
The correct matches represent the direct points of disagreement outlined in the passage: magma depth (deep core-mantle boundary vs. shallow upper mantle), mobility (stationary vs. migrating), and age progression driver (plate velocity vs. crack propagation velocity).

Step-by-Step Solution

1
Analyze Scientist 1 and Scientist 2's views on the origin of hotspot magma.
Scientist 1 places the origin at the core-mantle boundary (2,900 km2,900\text{ km}), while Scientist 2 places it in the shallow upper mantle (<200 km< 200\text{ km}). This matches the depth of origin to the first contrasting pair.
To identify the point of disagreement regarding magma depth.
2
Analyze Scientist 1 and Scientist 2's views on the mobility of hotspots.
Scientist 1 states that the plume is stationary relative to the plates, while Scientist 2 states that the hotspot location is not stationary and migrates with stress patterns. This matches the mobility of the hotspot source to the second contrasting pair.
To identify the point of disagreement regarding hotspot mobility.
3
Analyze Scientist 1 and Scientist 2's views on what determines the rate of volcanic age progression.
Scientist 1 links the age progression to tectonic plate velocity, while Scientist 2 links it to the velocity of crack propagation. This matches the age progression factor to the third contrasting pair.
To identify the point of disagreement regarding volcanic chain age progression.

Key Concept

Identifying Points of Disagreement
Rate this question

Topics

Identifying Points of Disagreement

More questions from this topic