Kayakers drawn to the legendary sea caves along the Apostle Islands National Lakeshore have been able to explore them in recent years without being caught off-guard by potentially deadly waves - thanks to a real-time wave observation system developed by the University of Wisconsin-Madison.

High waves that can flip a paddler into cold water may swell in and near the caves during certain weather conditions. Most kayakers launch near Cornucopia at Meyers Beach, about a mile southwest of where the sea caves begin. The beach may be deceptively calm because water behaves differently there than against the sheer cliffs that envelop the sea caves, said Bob Krumenaker, superintendent of the national lakeshore.

The Apostle Islands are considered one of the best areas for day-use sea kayaking in the world. They attract more than 20,000 paddlers a year to explore the vaulted chambers and honeycombed passageways of the caves carved by nature into the red sandstone cliffs. The sea caves have blossomed in popularity in recent years.

The area also has been the scene of several deaths or close calls involving paddlers who overestimated their skills, were unprepared for Lake Superior’s bone-chilling water or were caught by waves in and near the caves.

When storm systems approach, large waves not conducive to kayaking generate plumes of spray and thunderous explosions as they bounce off the cliff walls and surge into the sea caves. Four kayakers died of hypothermia and a group of 31 kayakers had to be rescued in the seven years before the wave observation system was in place.

There have been no deaths since the real-time wave observation system developed by experts at UW-Madison and the University of Wisconsin Sea Grant Institute was installed a few years ago at the west end of the sea caves, closest to the beach, Krumenaker said.

The system enhances visitor safety by providing current information on wave conditions at the sea caves, plus wave trends during the past several hours.

Camera shows waves

With real-time information, kayakers may change their minds and wait until conditions are safe, said Gene Clark, a coastal engineering specialist with the UW Sea Grant Institute headquartered at UW-Madison.

A camera installed on top of the southern sea caves provides photographs of wave conditions and posts them at the website SeaCavesWatch.org. A wave sensor in the water that can measure a 100-square-foot area continuously records current wave height, water temperature and wind speed, and transmits it via a cellphone tower to the website, which gets 96,000 visits a year.

Kayakers can either go to the website on their smartphones before they head to the beach or access it from a special kiosk with a directional receiver at the Meyers Beach boat launch, Clark said. Cellphone access is spotty in the area, he said.

“We hear from the park ranger at Meyers Beach that kayakers really like having the kiosk,” Clark said.

The idea of the wave observation system surfaced several years ago when a summer class of coastal engineering students traveled to the Apostle Islands for a week with Clark and Chin Wu, a UW-Madison professor of civil and environmental engineering.

They were there to learn about measuring waves and currents. When they stopped by the National Park Service office, Krumenaker posed the question: Would it be possible to measure waves 15 miles away from the Park Service office at the sea caves and make that information available in real time to anyone with a vested interest in safety?

“It was difficult for park rangers to know wave conditions at the sea caves,” Clark said.

Several kayak outfitters were involved in fine-tuning the website to make sure it was a quick read and didn’t go too far into the weeds with information only a scientist could understand.

Hypothermia is a killer

Kayakers sometimes fail to choose an appropriate kayak for Lake Superior. Kayaks with enclosed cockpits and sealed bulkheads are recommended for paddlers in cold water, Clark said.

If paddlers are dumped in the cold water near the caves and can’t get back in their kayaks, the sheer cliffs make it impossible for them to get out of the water because there’s no accessible shoreline for a mile, Clark said.

The water at the surface may be 70 degrees, but below the surface the temperature may be as low as 45 degrees, Krumenaker said. Paddlers are advised to use wetsuits or drysuits. Wearing a life jacket doesn’t ensure survival, but it can extend survival time in cold water.

Ninety-five percent of the time, the water near the Apostle Islands sea caves is fine. It’s the 5 percent of the time when it’s not that experts worry about.

In the years before the observation system was launched:

In June 2011, a kayaking trip by four Winona State College friends turned tragic when waves put two paddlers in the water and one of them died of hypothermia. They were paddling the two miles from Little Sand Bay to Sand Island and encountered 4-foot waves outside the bay, which had been calm. The 20-year-old Minnesota man who died was wearing a life jacket and the bottom half of a wetsuit.

In September 2010, a kayaker died of hypothermia after he was dumped in cold water in Justice Bay off Sand Island.

In June 2007, two kayakers capsized between Meyers Beach and the mainland sea caves. One man died and the other was rescued and treated for hypothermia.

There was a dramatic rescue in July 2005, when 31 kayakers - girls from a Minnesota camp along with four camp counselors and four guides - encountered a line of intense thunderstorms.

And in August 2004, another man died of hypothermia after his kayak capsized in the caves near Meyers Beach.

Other uses

The camera at the top of a cliff overlooking the sea caves has turned out to be useful in the winter, too, so rangers could check ice conditions before people walked out to see ice formations in the caves. The ice often shifts in winter.

Thousands of tourists are attracted to the arctic landscape during the winter. By February, an ice bridge typically connects Sand Island to the mainland. Pillars of ice extend to the cliff tops, and icicles await tourists inside the sea caves. The formations change from chamber to chamber and from day to day.

Centuries of wave action, freezing and thawing sculpted the shorelines throughout the Apostle Islands National Lakeshore. The sea caves are on the north shore of Devils Island, Swallow Point on Sand Island, and along the mainland near the national lakeshore’s western boundary.

The wave observation system also has helped UW-Madison’s Wu to begin developing methods for detecting and forecasting rip currents elsewhere along Wisconsin’s Great Lakes shoreline, including a real-time warning system he developed for Port Washington along Lake Michigan.

SeaCavesWatch.org originally was launched by the National Oceanic and Atmospheric Administration, the Wisconsin Coastal Management Program and the Friends of the Apostle Islands, with support from the city of Bayfield and the National Park Service.

Under a new agreement, Wisconsin Sea Grant will continue to provide coastal engineering expertise and outreach assistance as needed for the next five years.