Estimating Valley Fill Thickness with a Gravity Survey

Bill Witte
,
University Of Alaska Fairbanks

Summary

We will make a gravity traverse of the Goldstream valley to determine the thickness of the valley fill. The exercise will take ~ 4hrs, working in two teams all students will get to function in each of the survey roles.

Context

Audience:

Typically we use this in a field mapping class.
Designed for a geophysics course
Integrates geophysics into a core course in geology

Skills and concepts that students must have mastered:

Survey design: Is the effect measurable with the tools available and executable in the time available?

How the activity is situated in the course:

Near the end of the class, to supplement more classic mapping meathods.

Goals

Content/concepts goals for this activity:

Students will make the measurements and reduce the data in MS Excel to determine the valley fill thickness given some assumptions.

Higher order thinking skills goals for this activity:

Students will develop and test models. Students are also confronted with the non-uniqueness of gravity modeling.

Other skills goals for this activity:

Description of the activity/assignment

Previous mapping exercises have dealt with well-exposed rocks, but this particular area runs into a problem with a thick valley fill on bedrock. We have some good estimates of the density contrast for the valley fill and bedrock. A prelab exercise asks the students to assign realistic densities to the units. In class we develop a model for the expected anomaly size for different thickness, then we go out and measure the anomaly and estimate the thickness.

Uses online and/or real-time data Has minimal/no quantitative component
Addresses student fear of quantitative aspect and/or inadequate quantitative skills
Uses geophysics to solve problems in other fields

Determining whether students have met the goals

Students must complete the gravity reduction in MSExcel and choose the valley fill model that fits the data best.

More information about assessment tools and techniques.

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