Glacial Hazards in Prince William Sound
The massive tidewater glaciers of northern and western Prince William Sound are among its most spectacular attractions. However, operating a vessel near active glaciers and through floating ice fields presents unique, serious risks. Standard navigation rules do not account for the dynamic, unstable nature of glacial ice.
Key Hazards for Mariners
1. Tidewater Glacier Calving & Waves
Tidewater glaciers (glaciers that flow directly into the sea) are highly active. They continuously drop colossal slabs of ice into the ocean—a process called calving.
- Calving Wave Hazard: The sudden impact of millions of tons of ice hitting the water generates massive, highly energetic waves. These displacement waves behave like sudden tsunamis, traveling rapidly outward and growing steep as they reach shallow shorelines or narrow channel walls.
- The Threat: These waves can easily swamp, capsize, or throw vessels onto rocky shores, and can completely crush kayaks and small powerboats.
- Action: Maintain a minimum safe distance of 1/2 mile (approx. 1,000 yards) from the face of any active tidewater glacier. Never enter the narrow shoals near glacier faces.
2. Unstable Icebergs & The Rolling Hazard
Icebergs floating in the Sound are melting and shifting their center of gravity continuously.
- The Roll Hazard: As an iceberg melts, it becomes highly unstable and can roll over violently without a moment’s warning. The rolling motion creates turbulent water currents, severe waves, and drops tons of submerged ice upward.
- The Submerged Mass: Only a tiny fraction (typically 10% to 15%) of an iceberg’s total volume is visible above the surface. The remaining 85% to 90% extends far outward and downward beneath the water.
- Action: Never approach closely, tie your vessel to, or attempt to climb on any floating iceberg. Give all icebergs a wide berth, as you may strike their massive, invisible underwater shelves.
3. Iceberg Fields & Growlers
Glacial ice fields are filled with “growlers” (dull, dark ice chunks about the size of a car that float nearly fully submerged) and “bergy bits” (medium-sized ice blocks).
- The Collision Hazard: Growlers are extremely dense and hard. Striking a growler at speed can tear a hole in a fiberglass hull, destroy outboard propellers, or crush a kayak’s hull. Dark or clear ice is exceptionally difficult to spot in low-light, rain, or fog.
- Action: When transiting through ice fields, reduce speed to minimum maneuvering speed. Station a dedicated lookout at the bow to scan specifically for low-floating growlers. Turn off autopilot and steer manually.
Operating Rules in Ice Fields
- Never Attempt to Outrun Calving Wave: If you observe a calving event, immediately steer your bow directly into the oncoming wave. Keep passengers low and secured in the center of the vessel.
- Avoid Dense Ice Fields: If the ice coverage is tight enough that you must push chunks aside, do not proceed. Turn back or seek an alternative route. Glacial winds and tides can shift ice fields rapidly, trapping a vessel within minutes.
- Listen for Sound Warnings: Calving is preceded by loud, thunderous cracking sounds. If you hear deep rumbling, immediately scan the glacier face and prepare for waves.