Welcome to the “crater” that is not really a crater.
This giant valley atop Mount Haleakala has been called a “crater” since at least the first written mention of it in the early 1800s. In recent years, the National Park Service has emphasized the fact that the great depression at the summit is not a volcanic crater, but the result of erosion. This long-standing name results from early visitors’ attempts to explain how such an enormous valley appeared at the top of the great mountain.
The original settlers of this island had their own explanation of the origin of the valley. Obviously, it was the work of the volcano goddess Pele, famous for creating and destroying land.
When the first Westerners peered down over the rim of this ancient volcano, however, they began to come up with their own theories about the formation of what looked to them like a “crater.” Some visitors in the 1800s seemed to think the gaps had been formed by the rush of flowing lava in an ancient eruption. Some thought the giant depression had been formed when the volcano exploded, blowing off its top, while others believed the top of the mountain had collapsed, creating a caldera like that at the summit of Kilauea. It would be more than a century before someone settled on a scientific answer.
At least one scientist had suggested, in a 1915 paper for the USGS, that “what is commonly called the crater of Haleakala appears to me to be, in some part at least, a result of erosion.” But only when Harold A. Sterns made the first detailed study of the geology of Haleakala did a clear picture appear of the summit valley’s formation. Sterns’ goal was to document Maui’s water resources in a comprehensive survey between 1932 and 1942. Along the way, he found evidence that clarified the origin of the great depression atop Haleakala
Sterns estimated that the mountain might once have been at least a thousand feet taller, until heavy rainfall began to cut away the two valleys of Ke‘anae and Kaupo. Rising sea level filled the lower valleys, widening them and leaving huge deposits of soil along the valley walls. Above, at the head of both valleys, accelerated erosion had carved farther into the summit. A cataclysmic mudflow in Kaupo about 50,000 years ago created the Kaupo Gap, and perhaps something similar happened at Ke‘anae, though Sterns found no geologic sign of such an incident.
Sterns’ explanation is now generally accepted as the explanation of how the great depression at the summit of Haleakala was formed—not by rushing torrents of lava, nor by volcanic explosions, but by the slow, steady, and ultimately very powerful forces of water and time.