Seamount

November 14, 2022

Hidden in the back section of today’s local newspaper was a story of the likely eruption of a volcano deep beneath the Pacific Ocean in the US Commonwealth of the Northern Mariana Islands.  The Northern Marianas are about 3,800 miles (6,115 km) west of Honolulu.  This is “likely” as scientists do not know for sure as the area is so inaccessible.  All indications are the Ahyi Seamount began erupting in mid-October, the US Geological Survey said Monday.  Ahyi seamount is a large conical submarine volcano.  Its highest point is 259 feet (79 m) below the surface of the ocean.  It is located about 11 miles (18 km) southeast of the island of Farallon de Pajaros, known as Uracas.  Scientists are checking satellite data to see if there’s discolored water, which could suggest material is coming out of the volcano, or if the activity is just shallow earthquakes.  Matt Haney, a USGS research geophysicist, said, “There’s nothing right now that suggests that this eruption will intensify and become a large eruption.  Still, mariners would want to avoid the immediate area.”  Ya think?   

When I looked online, I found a seamount is a large geologic landform that rises from the ocean floor but does not reach the water’s surface (sea level).  It is not an island, islet, or cliff-rock.  Seamounts are typically formed by extinct volcanoes that rise from the seafloor to 3,300–13,100 feet (1,000–4,000 m) in height.  They are defined by oceanographers as “independent features that rise to at least 3,281 feet (1,000 m) above the seafloor” and are characteristically of conical form.  The peaks are often hundreds to thousands of meters below the surface and are considered within the deep sea.  When forming the largest seamounts may breach the surface where wave action erodes the summit to form a flat surface.  After they subside below the surface these flat-top seamounts are called “guyots” or “tablemounts”.  The Earth’s oceans contain more than 14,500 identified seamounts of which 9,951 seamounts and 283 guyots have been mapped, but only a few have been studied in detail.  Seamounts are most abundant in the North Pacific Ocean and follow an evolutionary pattern of eruption, build-up, subsidence, and erosion.  In recent years, several active seamounts have been observed, including Kamaʻehuakanaloa (formerly Lōʻihi) in the Hawaiian Islands.

Seamounts are one of the most common marine ecosystems in the world.  Interaction between the seamount and underwater currents and their elevated position in the water attract plankton, corals, fish, and marine mammals.  Their attraction has been noted by the commercial fishing industry, and many seamounts support extensive fisheries.  There are ongoing concerns on the negative impact of fishing on seamount ecosystems, and well-documented cases of fish stock decline, for example with the orange roughy (Hoplostethus atlanticus).  Most (95%) ecological damage is done by bottom trawling, which scrapes whole ecosystems off the seamount and weakens the formation.  While naval vessels have collided with uncharted seamounts, the greatest danger is from flank collapse.  As the seamount gets older, outside material can seep into the seamount and put pressure on the sides, eventually causing a landslide with the potential to generate a massive tsunami. 

THOUGHTS:  I recall driving across the Bay Bridge and then along the Bay Causeway as a predicted tsunami was scheduled to arrive.  I did not pay too much attention, until I realized I had several miles of flat coast to drive before any possibility of exit.  While the predicted wave did not arrive, others have not been so fortunate.  The 100 foot (30 m) high tsunami wave that hit the Indian Ocean in 2004 killed an estimated 227,898 people in 14 countries and prompted a humanitarian response totaling more than US$14 billion.  When we identify and map a seamount, we can predict future problems.  When we destroy the ecosystems they create, we make the seamount weaker and risk greater damage.  Act for all.  Change is coming and it starts with you.