The Floating Lithosphere - Isostasy

Initial Publication Date: September 5, 2006 | Reviewed: November 1, 2012


This activity lays the mathematical underpinning for studying isostasy in the Earth. Students numerically and then analytically determine the relations governing the depth of compensation in a variety of situations including a block of ice floating in water. Students recreate spreadsheets shown in the PowerPoint module on their own with formulas that answer various pieces of the overall question. This modules is the first in a set of three exploring isostacy.

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Learning Goals

  • Gain conceptual understanding by exploring the analogy of ice floating in water.
  • Numerically determine the difference in floating levels between oceanic and continental crust.
  • Analytically derive this difference in floating levels.

Context for Use

This module was designed to be used in an undergraduate mathematical geology class where students are asked to look at geological questions mathematically and may spend more time on the math than on the geology.

Description and Teaching Materials

This module is one of several developed by Dr. Vacher. The module presentation can be found at

The Powerpoint file is considered to be the student version. There is also an instructor's version that has active spreadsheets in it. There are instructions for requesting this version on the website.

Teaching Notes and Tips

These modules were developed as essentially self-paced, take-home lab assignments. Students are supposed to work through the modules, slide by slide, building their own worksheets as they go along, taking note of instructions and prompts, hints, and queries.

Students must have access to computers equipped with a spreadsheet program such as Excel.


The easiest way to test student work on this module is to ask students to hand in a copy of their worksheets starting with a different set of input data. The module also ends with homework assignment questions.

References and Resources