1.1C: Intra-Plate Stuff
The causes of intra-plate earthquakes, and volcanoes associated with hot spots from mantle plumes.
Intra-Plate Earthquakes
Earthquakes can occur in mid-plate settings, usually associated with major ancient fault lines being re-activated by tectonic stresses. For instance, the New Madrid Seismic Zone on the Mississippi River generates earthquakes up to magnitude 7.5, but is thousands of miles from the nearest plate boundary.
Hotspot Volcanoes
Some volcanic eruptions are 'intra-plate' meaning there are distant from a plate boundary at locations called mid-plate hotspots, such as Hawaii and the Galapagos Islands.
At these locations:
Mantle plumes are concentrated areas of heat convection. At plate boundaries they are sheet-like, whereas at hot spots they are column like.
At these locations:
- Isolated plumes of convecting heat, called mantle plumes, rise towards the surface, generating basaltic volcanoes that tend to erupt continuously.
- A mantle plume is stationary, but the tectonic plate above moves slowly over it.
- Over millennia, this produces a chain of volcanic islands, with extinct ones most distant from the plume's location.
Mantle plumes are concentrated areas of heat convection. At plate boundaries they are sheet-like, whereas at hot spots they are column like.