Restless Seamounts

While the spectacular Mauna Loa lava flows have been getting all the attention in the last couple of weeks, another volcano is making noise 3,800 miles west of Hawaii. Ahyi, a submarine volcano in the US territory of the Northern Mariana Islands, began erupting underwater in mid-October. Hydroacoustic sensors on Wake Island, 1400 miles away, were the first to pick up the sounds of activity, and data from seismic stations on Guam and a Japanese island confirmed the location. Ahyi has continued to rumble and belch sulfur, discoloring the seawater several hundred feet above and leading to an “Advisory” volcano alert level and a Code Yellow aviation warning. Ahyi doesn’t have the visual excitement of bright red lava oozing across the landscape but is a reminder that our earth continues to build and change in its own time.

The Pacific Ocean has thousands of seamounts that build from the ocean floor as hotspots of upwelling lava erupt beneath the crust. Lava begins to pile up in a conical shape on the ocean floor and over eons repeated volcanic eruptions push the cone upward, ever restless, ever building. The submarine volcano is called a seamount when it rises more than 3000 feet from its base and when it breaks the surface of the sea, it becomes an oceanic island. Industrious corals then colonize and encircle the top, building a fringing reef. That’s the long story of Wake Island, the ”slender stem” of which reaches two miles to the ocean floor.. I will never forget diving on Wake’s gorgeous fringing reef and peering over the edge into the deep blue.

Unlike isolated Wake, Ahyi lies along a string of about sixty active submarine volcanoes in the Marianas Volcanic Arc, just eleven miles from its neighboring volcanic island of Uracas. The Arc is six hundred miles west of and parallel to the Mariana Trench, which is the world’s deepest zone at about 36,000 feet. In recent decades scientists have gained more accurate data on depths using long-range side scan sonar and multi-beam technology. A 2003 NOAA expedition studied the “Ring of Fire” region of the Pacific and determined that the Marianas Volcanic Arc seamounts average 1.7 miles to the ocean floor. Two years after Ahyi last erupted in 2014 divers on a NOAA Deepwater Exploration team observed a new crater near the summit and a new landslide down the southern flank. Likely that view is changing as we speak.

Over millions of years the Pacific’s young, restless seamounts like Ahyi will build toward the surface and older volcanic islands – including Wake – will erode, subside, and sink back down to the ocean floor. This week as we honor the anniversary of the attacks on Pearl Harbor, Wake Island, and other targets across the Pacific, consider what a small dot human history is in the grand sweep of things on this planet.