Stage 1 is the initial stage of development. Fissures or small vents open on
the sea floor and produce pillow lava.
The volcano grows by adding layer upon layer of new pillow lava. Calderas
are possible. Lava is alkalic in composition, with higher abundances of sodium
and potassium relative to the tholeiitic basalts of the shield-building stage. Photograph of pillow lava by Gordon Tribble,
U.S. Geological Survey.