Turnagain Arm Tidal Bore Earthcache
In Alaska, United States
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Large Tidal Bores are only found in the United States in upper Cook Inlet on Alaska’s southcentral coast. Turnagain Arm (just south of Anchorage) experiences the largest in North America, at times generating a wave up to six feet in height moving as fast as 15 - 20 mph. This cache introduces you to how the unique combination of topography and tidal range in Turnagain Arm produces this regularly observable event, seen nowhere else in the USA.
To log this cache, position yourself to observe the tidal bore using the information below, and post a photo of the wave with your GPS in view. EFFECTIVE OCT 16, 2005 - IN ORDER TO MEET NEW EARTHCACHE GUIDELINES - Your log MUST include the time of your discovery, your coordinates along Turnagain Arm (posted as a waypoint with your photo), and an estimate of tidal bore wave height and speed. Could you outwalk or outrun the wave?
View the 2016 Bird Point and Beluga Point Bore Tide Schedule - courtesy of Alaska.org
A tidal bore is a wave generated by a sudden influx of water rushing in to an estuary following low tide. The prime ingredient for a tidal bore is a coastal tide range in excess of twelve feet. Turnagain Arm’s extreme tides are over 39 feet, the second largest range in the world after the Bay of Fundy in Nova Scotia. The length of Turnagain Arm contributes to the large wave height, as the ‘slosh’ or resonance of the water flowing into the relatively shallow arm coincides almost exactly with the nearly twelve-hour frequency of tidal movement. The largest wave occurs during the periods of lowest tides. After low tide in Anchorage, the tidal bore should reach Beluga Point 1 1/4 hours later and Bird Point 2 1/4 hours later – give yourself plenty of time to get in place and ready yourself to witness a dramatic sign of the changing tide.
The terrain resembles Scandinavian fjords with mountains rising up dramatically from the edge of the water. However, water depth is actually quite shallow at high tide, with large silty mudflats exposed at low tide. Do not venture out on the mudflats! The silty mud is deceptive – it can trap you and hold you in place with no time for rescue before the swiftly-advancing tidewaters drown you. Locals have story after story of persons who’ve discounted the danger of the mudflats, and have paid the ultimate price for their carelessness. See the awesome streaming video link in Moun10Bike's 9/20/05 post as part of his visit to Alaska during the Great Alaska Cache'N'Dash (thanks, Moun10Bike!)
(Anchorage Daily News photograph by Scott Moran)
A State Trooper helicopter prepares to rescue a kayaker (in the water to the right of the helicopter) who was separated from his kayak in Turnagain Arm near Bird Flats July 29, 2007. The rapidly shifting tides propelled a wall of water called a bore tide his way, catapulting him from his boat in currents so strong they sucked the clothes off his body. The Trooper helicopter happened to be nearby on another call and retrieved the kayaker before he was swept all the way to Portage.
The currents here are not as benign as they look - stay off the water!
Turnagain Arm is bordered directly by the Seward Highway on Anchorage’s south side, a designated National Scenic Byway with spacious pullouts positioned to provide dramatic vistas of the valley. This roadway makes possible a ‘chase’ of the tidal bore’s wave from pullout to pullout as it flows into the arm from west to east. A large and well-furnished wayside is at the promontory known as Bird Point. From here, it’s possible to see (and hear) the wave approaching from the west, and track its progress as it sweeps eastward into the upper reaches of the Arm. This accessible location is equipped with clean and spacious bathrooms, good parking for large vehicles, interpretive signs and exhibits detailing both the Tidal Bore and the beluga whale (commonly seen in Turnagain Arm during the summer months), and an excellent walkway out to an observation point with telescopes. As this is a part of Chugach State Park, there is a $5 parking fee to be paid within thirty minutes of your arrival. Bird Point is named for the flood of raptors and other travelers seen here during spring at this funnel point on the migratory flyway to the state’s Arctic region. This is listed as the cache location, but there are many other outstanding viewpoints along the Arm offering close looks at the Tidal Bore.
These recommended pullouts are in order from Anchorage towards Girdwood:
• Beluga Point – N61 00.395 W149 41.870 - This large turnout is a popular spot for sunset photography year-round and as a spotting site for beluga whales and Dall sheep. (No facilities)
• Windy Corner – N60 59.059 W149 36.608 - During the summer months windsurfers are sometimes seen here challenging chilly waters to take advantage of the steady wind. (No facilities)
• Bird Point – entrance to wayside at N60 55.825 W149 21.395 with best viewing at N60 55.688 W149 21.395. A paved pathway from here climbs up on the mountainside several hundred feet following the old roadway towards Girdwood, offering an easy hike with stunning views. Primary cache point with excellent facilities.
View the 2016 Bird Point Bore Tide Schedule
• Pullout – N60 56.205 W149 16.135 – This parking area is within feet of the water, and is my personal favorite for getting action shots of the kayakers and surfers who choose to challenge the Tidal Bore’s wave. A relatively deep but narrow channel close inshore that’s easy to reach draws these local extremists to this and several other pullouts between Bird Point and Girdwood in the summer months. Reserved Handicap Parking spots, good clear viewpoints close to the water and no parking fee makes this an excellent choice relative to Bird Point - but there's no bathroom facilities here!
Visit this site to learn more about the EarthCache concept (and how to earn the EarthCache Master Pin!):
The Geological Society of America (GSA) EarthCache Project
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Last Updated: on 1/23/2017 4:57:28 PM (UTC-08:00) Pacific Time (US & Canada) (12:57 AM GMT)
Coordinates are in the WGS84 datum