3. Dips and Contours

Strike

The direction where there is no tilt in a plane, is perpendicular to dip direction

Dip

The maximum tilt in a plane (steepest angle)

Dip Direction

The specific compass bearing of that steepest downward slope

Right-Hand Rule

A convention for determining the orientation of a tilted rock layer by pointing the fingers of your right hand down the dip direction and your extended thumb to the strike direction

Azimuth Convention

Defines direction as an angle measured in degrees clockwise from a reference point, most commonly North, on a 360-degree circle, where 0° is North, 90° is East, 180° is South, and 270° is West

Quadrant Method

A way to describe directions and the orientation of geological features using a compass, where directions are given as an angle (0-90°) measured from either North or South, followed by the direction East or West

Clar Notation

A method for recording the orientation of geological planes using a compass to measure the strike and dip simultaneously, noting that the dip direction is 90 degrees clockwise from the strike

Plunge Direction (Trend)

The direction of line in the horizontal plane

Plunge

The vertical angle between the horizontal plane and the line

Grading

The sorting/settling of geological sediments by size, which can indicate things such as the direction of flow

Turbidity Current

A dense, sediment-laden underwater current that moves rapidly down a slope due to gravity

Cross-Bedding

A sedimentary structure where layers within a larger bed are angled relative to the main horizontal bedding plane

Younging Direction

Indicates the upward direction of deposition in sedimentary or volcanic sequences

Outcrop

A visible exposure of bedrock

Subcrop

A boulder from an outcrop that hasn't moved far from its original location

Lithological Contact

The contact between two different rock types

Contour Lines

Lines that show equal areas of elevation projected onto a horizontal surface to make a structure contour map

Outcrop Patterns

The visible surface shapes of rock layers, faults, or folds on the Earth's surface, formed by the intersection of these geological features with topography

Rule of V's

By looking at the map view pattern of the contact and the contour lines, one can determine the dip direction of the contact

True Dip

The maximum angle at which a geological layer is inclined from the horizontal, measured in a vertical plane perpendicular to the strike; the maximum dip of a plane

Apparent Dip

The maximum dip that we can see and measure; any observed dip in a different direction and it is always less than the true dip

Obliquity Angle

The angle between dip direction and cross-section showing the apparent dip

Three-Point Problem

Allows you to find the orientation (strike and dip) of a plane using three points; you only need the spatial location of three points to define a plane

Structure Contour

A line that connects points of equal elevation of a geological structure