“No stratigraphic or constructural evidence was found to support the hypothesis that Haleakala Crater is a true caldera, that it was formed by renting, or that Keanae and Kaupo valleys tapping this depression are grabens. Instead, detailed mapping and the examination of water tunnels show that Haleakala dome has been eroded by a number of great valleys. The hypothesis is presented that the so-called “crater” of Haleakala is chiefly, if not entirely, the result of the coalescence of the amphitheater heads of Kaupo and Keanae valleys and that renewed volcanic activity has partly masked their former divide and partly filled these valleys with lava flows.”
Haleakala rises above the belt of warm trade winds into the cold, dry climate of the Alpine Zone. Temperatures at night may drop below freezing even in the warmer part of the year; the growing season is short and life is severe. The sparse plants that can live here crouch closely to the ground, diffusing or forming compact rosettes. All they have in which to grow are porous rocks and loose cinders that cannot hold moisture, lack organic matter, and do not yield a firm base for rooting. Species extending to lower elevations are here depauperate from wind and cold, although elsewhere they may attain a sturdy stature, even tree-size. Few seedlings are seen; individuals whose life span has finished remain conspicuous in death. Neither trees nor mats of shrubs are seen, but mosses and lichens find this Alpine desert to their liking. Oddly enough, one looks in vain for brilliant blossoms, such as one has come to expect in the high Sierra and the Rockies. The summit is a biological island on an oceanic island which, geological evidence indicates, never was part of a continent. The Hawaiian Chain was never near land of appreciable height and size.
How the Alpine plants came to Hawaii is uncertain since they have descended from ancestors so remote that past relationships are vague. The great Swedish botanist, Carl Skottsberg, believes that they are derived from a flora that grew on summits higher than any that exist today. Such assumption adds to the problem, as little else leads one to believe that elevations ever significantly exceeded 14,000 feet, i.e., the highest that exist today. In a report for the Fifth International Botanical Congress (Proceedings, pp. 91-97, Cambridge, 1931), Skottsberg listed 13 species found exclusively in the Alpine Zone, all of which are endemic, native to no other place than Hawaii’s highest volcanoes. Three other species listed as occurring in the Alpine Zone extend their range downward into the next lower Subalpine Zone, for which he has listed a total of 23 species, 20 of which he labels endemic. These adjoining zones are not sharply delimited, but blend into each other at 9,000 feet.