More than 5‐million years ago, a hotspot in the earth spewed lava upward to form the volcanic mountain island of Kaua‘i. Nearby Hā‘upu Ridge and Mountain contain some of the oldest geologic formations. The youngest volcanic cones, such as Pu‘uwanawana, produce weathered volcanic material creating rich agricultural plains.
As their name suggests, cinder cones consist of cinders, more properly called scoria. Scoria is very vesicular, low density basalt.
Lava fountains are driven by expanding gas bubbles; the bubbles are trying to expand in all directions but the only way to relieve the pressure is up out the vent so fountains are usually directed relatively vertically.
￼Cinder cones are the simplest type of volcano. They are built from particles and blobs of congealed lava ejected from a single vent. As the gas‐charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone.
￼Most cinder cones have a bowl‐shaped crater at the summit and rarely rise more than a thousand feet ￼or so above their surroundings. Cinder cones are numerous in the various volcanic terrains of the world, ￼including Hawaiʻi.
The circular ridge is the remains of the edge of the cone. The ground drops down inside the ridge into the caldera. The cone and its caldera are covered in tall scrub and cactus. A number of other cinder cones are within the Scenic Byway corridor.