The Triton


Sea Science: Altered coastlines may require an alternate route


Sea Science: by Jordanna Sheermohamed

Navigating a yacht requires advanced knowledge of the intended transit route, either via previous experience or access to the most up-to-date information for planning purposes.

As recently witnessed with the sudden emergence of “Shelley Island” in the Diamond Shoals area off of Cape Hatteras, the coastline can literally change overnight. It’s obvious to see how this would pose a dangerous problem for a yacht in the vicinity of the altered region if the captain were unaware of these changes while in transit.

When questioned about who was tasked with charting these changes, the NOAA Office of Coast Surveys relayed that “hydrography is not charted for Diamond Shoals due to the changeable nature of the area. Navigation in the area is extremely hazardous to all types of craft.” Furthermore, a caution note was already charted for the region because of its volatile nature, so the Office of Coast Survey would not have issued a separate Notice to Mariners (NTM) about Shelley Island.

However, the U.S. Coast Guard did reference the emergence of the island in its weekly Local Notice to Mariners (LNM), specifically within the May 27 release. The exact coordinates of the new island were also provided so that extra caution could be exercised.

The NOAA Navigation Services relayed that changes to the shoreline are generally charted more frequently when a higher traffic area is affected, and that multiple offices work in tandem to gather this information. But these changes may disappear as fast as they appear, and sometimes this happens between surveys. Depending on the location and frequency of navigation in the altered area, digital charts may be updated as early as three weeks, or may take as long as four to five months. Meanwhile, the changes would not be included in a vessel’s current arsenal of printed navigation charts.

The Shelly Island phenomenon is one of many stories of navigable waters changing in a short time. This can happen for a number of reasons. For instance, an impending storm system may approach from an anomalous direction, which can potentially relocate massive amounts of sand or rock sediments quickly.

Geological activity such as volcanoes can also instigate rapid land alterations by shifting ocean flooring or producing lava, which cools into an igneous rock when it reaches the water. The former scenario was observed when a 7.7 earthquake in northwest Pakistan indirectly produced a pocket of methane gas off the coast. Two days later, this pocket erupted and thrusted ocean floor mud upward. The newly formed island lasted about a year before the ocean crust eventually compressed, and the land mass retreated into the sea.

Land masses that are backed up against a major water basin can be subjected to relentless wind and wave activity, which can steadily etch away at a coastline. Eventually a counteraction may occur when a tipping point is reached, which acts to balance the newly shifted load. This was thought to be the case in the rapid appearance of the northern Japanese island Hokkaido, which on April 24, 2015, rose nearly 33 feet out of the water overnight along the east coast.

Even with as much advanced planning as possible, additional equipment and watchful eyes may be necessary to account for these rapid changes. It’s important to consider that, while notification of alternating coastlines may fall under the jurisdiction of the multiple entities, the safety of actually navigating changing waters falls on the shoulders of yacht captains themselves. This underlines why every captain needs to be familiar with the intended route and its capacity to change.

Jordanna Sheermohamed is president and lead meteorologist of Weather Forecast Solutions, a private weather-forecasting company (  Comments are welcome below.

About Jordanna Sheermohamed

Jordanna Sheermohamed is president and lead meteorologist of Weather Forecast Solutions, a private weather-forecasting company ( Comments are welcome at

View all posts by Jordanna Sheermohamed →

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