What Does the Mean Mean? Describing Eruptions at Riverside Geyser, Yellowstone National Park

Module by: Tom Juster, University of South Florida

Cover Page by: Len Vacher and Denise Davis, University of South Florida

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This material was originally developed by Spreadsheets Across the Curriculum as part of its collaboration with the SERC Pedagogic Service.


In this Spreadsheets Across the Curriculum activity, students build on their work with the frequency (histogram) of eruption intervals of Old Faithful ("Just How Faithful is Old Faithful?") by exploring 2007 and 2008 data from Riverside Geyser, which turns out to have a bimodal distribution. The module assumes the students can build a histogram from tabulated data and can easily move around in a large spreadsheet, skills presented in the Old Faithful module. The module repeats all the introductory material on Yellowstone, the workings of geysers, and the reasons for monitoring eruption intervals, so that the module can stand alone if students are proficient in Excel. The new material of this module concerns the measures of central tendency of a frequency distribution (mean, median and mode). The histogram shows that mean (or median) value occurs very infrequently in this example using real data.

This material is based upon work supported by the National Science Foundation under Grant Number NSF DUE-0836566. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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Learning Goals


Students will:

  • Have the opportunity to review or catch up on background information on geysers at Yellowstone and how geysers work.
  • Practice what they learned in the Old Faithful module about making a histogram in Excel by plotting 2007 and 2008 eruption interval data at Riverside Geyser.
  • Calculate the mean, median, and mode.
  • Consider what the mean means in a bimodal distribution.

In the process the students will:

  • Burrow more deeply into the subject of frequency distribution.
  • Learn that not all distributions are the nice, symmetric, bell-shaped curves one sees in many diagrams.
  • Learn of a real-world case where the mean value hardly occurs at all.Gain a practical appreciation of the benefits of seeing a distribution in a histogram.

Context for Use


This module is designed for potential use in the Geology of National Parks service course at USF. The course is offered as an online course every semester. It includes readings from Parks and Plates, weekly quizzes based on that textbook, and weekly student activities designed to align the course with the University's general education requirements. This module is intended to be one of those activities, with the specific goal of meeting the gen-ed quantitative literacy dimension.

This module is one of four on Yellowstone NP, one of three on hydrothermal features, and one of two specifically on geysers. From least to most challenging, and most general to most specific, the order of the four modules is: (1) "Yellowstone! A National Park on a Hot Spot," (2) "A Percentage Stroll through Norris Basin," (3) "Don't Mess with Old Faithful" and (4) this module. Much of the introductory material in this module repeats the introductory material in the Old Faithful module, so these last two can be used individually or in succession.

Description and Teaching Materials


The module is a PowerPoint presentation with embedded spreadsheets. Click on the link below to download a copy of the module.

Optimal results are achieved with Microsoft Office 2007 or later; the module will function in earlier versions with slight cosmetic compromises. If the embedded spreadsheets are not visible, save the PowerPoint file to disk and open it from there.

The above PowerPoint presentation file is the student version of the module. It includes a template for students to use to complete the spreadsheet(s) and answer the end-of-module questions, and then turn in for grading.

An instructor version is available by request. The instructor version includes the completed spreadsheet. Send your request to Len Vacher (vacher@usf.edu) by filling out and submitting the Instructor Module Request Form.

Teaching Notes and Tips

The module is constructed to be a stand-alone resource. It can be used as a homework assignment, lab activity, or as the basis of an interactive classroom activity. The Old Faithful and Riverside Geyser pair of modules was used as an out-of-class activity in Computational Geology (a QL course for geology majors) midway through the semester in Fall 2010 and Fall 2011 after the students had worked through a few other modules. The students considered these modules to be at an average level of difficulty, well in line with their expectations, and they appreciated the practice with constructing the histograms. The modules have not been implemented in the introductory-level Geology of National Parks course.


There is a slide at the end of the presentation that contains end-of-module questions. The end-of-module questions can be used to examine student understanding and learning gains from the module. Pre/post test, pre/post test answer key, and answer key for end-of-module questions are at the end of the instructor version of the module.

References and Resources

The Geyser Observation and Study Association (GOSA)

Riverside Geyser

  • gosa.org/geyser.aspx?pGeyserNo=RIVERSIDE (link unavailable)

Town area: Look under Geography and weather: Topography for total city area.

US National Park Service (NPS)