Dikes

Dikes, in geology, are tabular igneous intrusions that cut across existing rock formations. They form when magma intrudes fractures and conduits in the surrounding rock and crystallizes. Dikes are discordant with the host strata, typically vertical or steeply inclined, and can extend from meters to kilometers. They differ from sills, which are parallel to layering. Dikes vary in mineralogy from mafic to felsic and often display chilled margins where cooling is rapid. Their study helps reveal magma transport directions, the timing of magmatic events, and the tectonic history of a region.

Outside geology, the term dike (often spelled dyke) also refers to flood-management embankments built along coasts, rivers, or lakes to prevent flooding from high water. In the Netherlands and other delta regions, dikes are part of long-term water-management systems, reinforced with earth, rock, concrete, drainage, and pumping facilities. Dikes require ongoing maintenance to address seepage, erosion, overtopping, and foundation settlement, and are affected by climate change and extreme weather.

Spelling varies by region: dike, dyke, and dijk (in Dutch) reflect regional usage. In scientific literature, dike is the common spelling in American English; dyke is common in other varieties of English.