Heavy mineral compositions of sands from Oregon beaches,
rivers and sea cliffs have been determined in order to examine the
causes of marked along-coast variations in the beach-sand
mineralogy. The study area extends southward from the Columbia
River to the Coquille River in southern Oregon. The heavy-mineral
compositions were determined...
Concern regarding increased coastal erosion has heightened amid growing acceptance of global warming and associated sea-level rise. This study examines shoreline erosion in Flathead Lake, Montana due to five decades of artificially elevated lake levels. It provides a model to investigate coastal erosion associated with sea-level rise. The natural water...
Straight, radial, erosional channels and fan-like deposits of tephra develop around steep-sided cones and composite volcanoes, but are not characteristic features of shield volcanoes. The channels and deposits normally are formed by explosive volcanic density currents which originate as nuées adrentes or base surges. The physical processes of explosive volcanic...
Field observations are made of the formation of backwash ripples
on the beachface, formed by undular hydraulic jumps generated by backwash
down the beach face colliding with wave bores. Measured ripple
wavelengths range from set averages of 48 to 70 cm. Within a particular
set of ripples there is a...
The formation of beach placers primarily involves processes of
waves and currents that selectively sort and concentrate the valuable
minerals according to their densities, sizes and shapes. Black sand
placers are found on the beaches adjacent to the mouth of the Columbia
River. Reviews of historical shoreline changes show that...
Grain-size distributions of gravels transported as bedload in Oak Creek, Oregon,
show systematic variations with changing flow discharges. At low discharges the gravel
distributions are nearly symmetrical and Gaussian. As discharges increase, the
distributions become more skewed and follow the ideal Rosin distribution. The patterns of
variations are established by...
Sea-cliff erosion is a significant problem along the Oregon coast in that many
communities have been built on terraces affected by bluff retreat. There is considerable
coast-wide variability in the rates of cliff erosion. This variability is attributed in part to
tectonic activity that is causing differential interseismic uplift along...