Geoscience for Central Vancouver Island Communities
Our Dynamic Coastline
Topics on this page:
Sedimentary Coasts
Coastal Challenges
Weird Weathering
Sedimentary Coasts
Fantastic Beaches Vancouver Island's famed beaches, including those at Parksville and Qualicum Beach on the east coast and in Pacific Rim National Park on the west coast, occur where waves erode sand and gravel from cliffs of glacial deposits or from river-mouth deltas. During winter, many beaches shrink as storms move sand offshore. The sand is carried back to the beaches by smaller waves and currents in summer.
Resistant metamorphic rocks form rocky headlands while soft glacial deposits erode into sandy beaches, Long Beach, Pacific Rim National Park.
Beaches and coastal cliffs can be eroded, threatening nearby structures. Harbours may 'silt up', requiring periodic dredging to maintain navigable waters. Earthquakes may trigger submarine landslides or tsunamis that damage docks and other coastal structures.
Sandstone shorelines can weather into strange forms. Examples in the Nanaimo area include the cave-like 'Malaspina galleries' and honeycomb weathering along the shores of the Gulf Islands.
The cause of the strange shapes is related to variation in the mineral cement that holds sandstone together. Cemented sandstone is more resistant to erosion and forms ridges, 'lips', and cannonball-like 'concretions', whereas sandstone that is only partially cemented will erode more easily, resulting in depressions and caves.
