USGS Geology in the Parks
Green Sand Beach, Hawai'i
The architecture of the cinder cone, as can be seen in the layers
of erosion-resistent cliff-formers, represents individual ash and
cinder eruption events. When the volcano erupts, the ashes are tossed
into the air and fall on the slopes of the volcano. Sometimes these
ashes and cinders are still hot enough to meld together, forming
cohesive layers which are more difficult for the ocean to erode.
From this view it is possible to not only see the internal structure
of the cinder cone, but also the profile of the beach. This is not
a wide, barely sloping expanse of sand, but a narrow, steep slope.
The same wave energy that causes the olivines to be left behind
shapes the beach into a steep slope.