B.9. Concept Of Seafloor Spreading
[Image: The Process of Seafloor Spreading]
Conventional current theory, mapping of the ocean floor, and the concept of Continental drift theory revealed that
- All along the mid-oceanic ridges, volcanic eruptions are common and they bring huge amounts of lava to the surface in this area.
- The rocks equidistant on either side of the crest of mid-oceanic ridges show remarkable similarities in terms of the period of formation, chemical compositions, and magnetic properties.
- Rocks closer to the mid-oceanic ridges have normal polarity and are the youngest. The age of the rocks increases as one moves away from the crest.
- The ocean rock is much younger than the continental rocks.
- The deep trenches have deep-seated earthquake occurrences while in the mid-oceanic ridge areas, the quake foci have shallow depths.
These facts and a detailed analysis of the magnetic properties of the rocks on either side of the mid-oceanic ridge led Hess (1961) to propose his hypothesis, known as the “seafloor spreading”. Hess argued that constant eruptions at the crest of oceanic ridges cause the rupture of the oceanic crust and the new lava wedges into it, pushing the oceanic crust on either side. The ocean floor thus spreads.