Essentials of Oceanography

Activity 3


Hotspots and Ocean Floor Morphology

Hotspot tracks on the ocean floor were one of the first smoking guns for the theory of plate tectonics, and they were also one of the conundrums. Early evidence showed that hotspots were more or less fixed in space; they did not seem to move relative to one another. This led to the idea that they originated at great depth. But how could a narrow plume of heat, or low viscosity material, rise through the convecting mantle without being offset? Early researchers pointed to the analogy of smoke rising through the atmosphere: on a windy day, the smoke plume was offset, and when the wind changed direction, so did the plume.

The images below shows a basic idea of how hotspots and linear island chains work.

basic idea of how hotspots and linear island chains work
Source: USGS

Activity 3


  1. Read each of these short papers:
  2. Post your responses to the following questions in the discussion area on Canvas for Lesson 2 Activity 3.
    • Why do hotspots form distinct volcanic islands, rather than a continuous linear axis?
    • What major change occurred recently in our thinking about Hotspots, and what were the data that led people to rethink the way hotspots work?
    • Many textbooks say that the change in trend of the Hawaiian Islands and the Emperor Seamounts represented a major shift in the direction of the Pacific plate motion ~ 43 Ma. Is that still thought to be true?
  3. Read the postings made by other EARTH 540 students.
  4. Respond to at least two other postings, per question, by asking for clarification, asking a follow-up question, expanding on what has already been said, etc. You should have at least six responses to other postings.

Submitting your work

  • I have begun this discussion activity by posting each of the 3 questions to the discussion on Canvas. Please click on the "reply" link that follows each question in order to post your response. To respond to another student's posting, use the "reply" link that follows their posting.

Grading criteria

You will be graded on the quality of your participation. See the grading rubric for specifics on how this assignment will be graded.