ASBOG Study Guide 2026

A river's longitudinal profile plots elevation against distance downstream; a knickpoint is an abrupt steepening or waterfall that disrupts the smooth concave-up graded profile, typically due to base level change or resistant rock.

The Rule of V's states that a dipping formation crossing a valley forms a V-shaped pattern pointing in the updip direction if dipping downstream, or pointing upstream if dipping in the same direction as stream flow but at a dip angle less than the stream gradient.

The Mohorovičić discontinuity, or Moho, is defined by a sharp increase in the velocity of seismic waves (both P-waves and S-waves). This velocity change marks the transition from the lower-density crustal rocks to the higher-density mantle rocks (peridotite).

Residence time reflects how long an element remains dissolved in seawater before removal; elements with long residence times (e.g., Na) are well-mixed, while those with short times (e.g., Al) are highly reactive.

In the Strahler system, unbranched headwater streams are order 1; when two order-1 streams join, they form order 2; when two streams of the same order n join, they form order n+1; junction of streams of different orders retains the higher order.

Induced seismicity refers to earthquakes triggered by human activities; deep-well injection of wastewater (primarily produced water from oil and gas operations) into crystalline basement aquifers in the central US has been responsible for a dramatic increase in earthquake rates, including M5+ events in Oklahoma, Kansas, and Ohio.