Ancient ahu dot the summit slopes of Mauna Kea. These stone shrines or altars are primarily found on the southern plateau near the adze quarry. There are dozens of sites scattered across the slopes, usually atop prominent rock outcroppings. The most typical structure is a stone pile or platform with a large upright stone at the center. A few sites have multiple uprights. The uprights are clearly carefully chosen, usually a long narrow pohaku.
These ancient ahu are usually modest constructions, none exhibiting the fine stonework visible in the heiau and other religious sites across the islands. The harsh weather of Mauna Kea has taken its toll, often the stones are scattered, the upright has fallen.
There is one modern ahu that has been around for a while, sometimes. At the very summit of the mountain an ahu can usually be found. Apparently there is some disagreement about the presence of this ahu. I have seen the stones scattered, I have seen the ahu reappear. When I first began working on Mauna Kea the summit this ahu had a lele, a simple wooden platform built over the ahu.
The current attention focused on Mauna Kea has seen a resurgence in the building of ahu as an act of protest. At least five have been built that I am aware of. Two at the TMT site, two in the middle of the gravel portion of the summit road, one alongside the summit road about halfway up the switchbacks.
These are typically much more substantial structures than the ancient sites. Actually quite well built, sometimes with local rock, at least one is built with rounded stream boulders brought from far below the summit. Unlike the ancient sites these new ahu are fairly standardized, a rock platform around 10-20 square feet in size with a single large upright at the center.
What is the status of these sites? What about an ahu built in the middle of a road?
I think it is pretty clear that an ahu erected with ill intent is not sacred. The entire question of sacred or not sacred is a question of intent. Setting an ahu in the middle of the road is simply not pono. Whatever motive the builder may have, creation of such a structure it is still a malicious act, a serious risk to any who use the road. The builders knew this as they stacked the stones. An ahu like this should be removed, preferably by those who erected it.
The two ahu have been removed from the summit road. A third still exists, the one built on a level area beside one of the switchbacks above Hale Pohaku, not in the road. As far as I am aware the two built on the TMT site still exist, both in the roadway. Whether they are dismantled or allowed to remain is still an open question.