Final answer:
The majority of Earth's volcanic activity, estimated to be around 70% to 90%, takes place on the seafloor due to seafloor spreading along active rift zones measuring about 60,000 kilometers in length.
Step-by-step explanation:
The question focuses on Earth's volcanic activity, specifically the amount that occurs on the seafloor. This topic falls under the subject of Geography, as it pertains to the geographical and geological features of the Earth's oceans. To determine the percent of volcanic activity on the seafloor each year, we can examine data related to seafloor spreading. It is known that about 60,000 kilometers of active rifts have been identified, which contribute to the creation of new oceanic crust at an average separation rate of about 4 to 5 centimeters per year, creating around 2 square kilometers of new area annually. This process, associated with volcanic activity at mid-ocean ridges, represents the majority of the Earth's volcanic activity.
Considering the extensive network of mid-ocean ridges and the consistent rate of seafloor spreading, it is estimated that the vast majority of Earth's volcanic activity, around 70% to 90%, occurs underwater along these rift zones. This percentage signifies the dominance of submarine volcanic activity in contrast to the volcanic activity visible on land. In summary, the seafloor is a highly active volcanic region due to the continuous process of seafloor spreading, which renews the entire oceanic crust over geological timescales.