Ocean-ridge volcanoes in particular have been observed to follow a certain pattern in terms of eruptive activity, first observed with Hawaiian seamounts but now shown to be the process followed by all seamounts of the ocean-ridge type. During the first stage the volcano erupts basalt of various types, caused by various degrees of mantle melting. In the second, most active stage of its life, ocean-ridge volcanoes erupt tholeiitic to mildly alkalic basalt as a result of a larger area melting in the mantle. This is finally capped by alkalic flows late in its eruptive history, as the link between the seamount and its source of volcanism is cut by crustal movement. Some seamounts also experience a brief "rejuvenated" period after a hiatus of 1.5 to 10 million years, the flows of which are highly alkalic and produce many xenoliths.
Ocean-ridge volcanoes in particular have been observed to follow a certain pattern in terms of eruptive activity first observed with Hawaiian seamounts but now shown to be the process followed by all seamounts of the ocean-ridge type During the first stage the volcano erupts basalt of various types caused by various degrees of mantle melting In the second most active stage of its life ocean-ridge volcanoes erupt tholeiitic to mildly alkalic basalt as a result of a larger area melting in the mantle This is finally capped by alkalic flows late in its eruptive history as the link between the seamount and its source of volcanism is cut by crustal movement Some seamounts also experience a brief "rejuvenated" period after a hiatus of 15 to 10 million years the flows of which are highly alkalic and produce many xenoliths