Final answer:
The geology of the Pacific coastal regions of Western North America is characterized by volcanic activity and mountainous terrain, with the area being part of the active Ring of Fire and having plate boundaries that lead to the formation of mountains such as the Cascade Range.
Step-by-step explanation:
The geology of the Pacific coastal regions of Western North America, including Alaska, is best described as volcanic activity and mountainous terrain (option a). This area is part of the Pacific Ocean's Ring of Fire, which is known for its high levels of seismic and volcanic activity. The plate boundaries along the West coast of North America consist of divergent, convergent, and transform faults with significant relative movements.
For example, the Juan de Fuca plate off the coast of Washington and Oregon is subducting beneath the North American plate, leading to the formation of the Cascade Range, including volcanic mountains such as Mt. St. Helens. The ultimate fate of the Juan de Fuca plate is to be completely subducted, causing volcanic activity and contributing to mountain building in this region. In this dynamic geologic setting, you can also find glacial deposits and fjords further north, but the predominant features along the Pacific Coast are related to tectonic activity and the resulting landforms.