Aialik and Holgate Glaciers both drain into Aialik Bay from the Harding Icefield. Aialik is the larger of the two and is located at the far north end of Aialik Bay, while Holgate is located in a western arm about halfway up the bay.
You will need a boat to access this Earthcache (although I suppose it could be possible to fly up the bay to get the answers!). If you don't have access to your own boat there are several charter services in Seward that take tours up Aialik Bay to view the glaciers. Typically these tours will visit only one of these two glaciers. The one they choose depends on the conditions at the time. Therefore you only need to visit one of the glaciers to qualify for this Earthcache. The cache page coordinates are set at the point where the routes to the two glaciers diverge.
What is a Glacier?
Glaciers form because snowfall in the high mountains exceeds snowmelt. Imagine a place high in the mountains that catches a vast amount of falling snow every year. This place is so high and so cold that none of the snow melts even in the summer. Over time, that snow pack builds. Soon the weight of the snowflakes in the upper layers of the snow pack presses down deforming the snowflakes beneath. The snowflakes in the pack first change to granular snow – round ice grains – and eventually morph into solid ice.
Glacier ice is different from the ice in your refrigerator. The ice crystals form slowly under pressure and individual crystals can grow to be the size of a football. Air trapped between the snowflakes is also frozen into the ice at pressure. Ice near the bottom of the glacier is under tremendous pressure, which allows it to flow almost like a plastic over the bedrock beneath. Friction between the glacier and the bedrock produces meltwater which further lubricates the bedrock allowing the ice to slide.
Tidewater Glaciers
If a glacier is fed by enough snow to flow out of the mountains and down to the sea, it is called a "tidewater" glacier - the type many people come to Kenai Fjords to see. These types of glaciers will break off or "calve" into saltwater at sea level. Tidewater glaciers are naturally dynamic, advancing and retreating in response to local climatic and fjord conditions. The show can be spectacular. As water undermines some ice fronts, great blocks of ice up to 200 feet high break loose and crash into the water.
When tidewater glaciers calve into the marine environment, the icebergs, bergy bits, and growlers serve as pupping and molting habitat for some of the largest seasonal aggregations of harbor seals in Alaska. Seals are frequently seen sunning themselves on the ice floes in the bay.
Icebergs:chunks of ice the size of a small house or larger (5 meters of ice above the water). Bergy bits: chunks of ice between the size of a small house and a minivan. Growlers: chunks of ice smaller than a minivan.
Tidewater Glacier Cycle
Unlike other glaciers, tidewater glaciers undergo a four phase cycle of advance and retreat that may take centuries to complete a single cycle. These cycles occur independent of climate changes, although a changing climate does exert varying degrees of influence during the different phases. The phases are Advancing; Stable Extended; Drastically Retreating; Stable retracted.
Characteristics of each phase:
Advancing: Moderate ice calving, the glacier has built up a terminal shoal of sediment and begins pushing it out into the water. If the shoal get pushed up above the water calving may completely cease for a time. The shoal protects the underside of the glacier from warm seawater and wave action, and slows the flow of the glacier itself. The glacier is not very sensitive to climate change during this phase.
Stable-Extended: The maximum extended position of the glacier. The terminal shoal supports the end of the glacier and protects the shelf behind it from wave action and warmer currents. The glacier will thin during this period. The glacier is sensitive to climate change during this phase.
Drastically Retreating: Once the glacier has thinned enough to lift the tongue of the glacier off the terminal shoal, the bottom of the glacier becomes exposed to ocean water, currents and motion and rapid melting on the underside of the glacier occurs. This weakens the ice shelf and ice calving occurs rapidly. The water body the glacier calves into may be filled with the icebergs that have broken off. Glacier flow may accelerate during this phase as the terminal shoal no longer holds it back. The glacier itself is comparatively insensitive to climate change during this phase, although it is possible that the retreat to new equilibrium conditions may be far more extensive than the next advance stage may gain.
Stable-Retracted: The glacier has reached a point where calving is reduced and the glacier begins to build a new terminal shoal. Full-sized icebergs are likely to be rare, although bergy bits and growlers are common.
To claim this Earthcache complete the following tasks:
1) Send a message or email to the cache owner and include the following:
- What phase of the Tidewater Glacier Cycle does the glacier appear to be in?
- Describe what you see that brings you to that conclusion.
2) In your log tell us:
- Which glacier you visited, Holgate or Aialik (or both!).
- About any ice falling from the face of the glacier during your visit.
- Whether seals were present on the ice floes in the bay.
- Pictures are not required, but always appreciated!
Information for this cache page derived from National Park Service; UAFairbanks; Hoover-Miller and Armato 2017; and Post and Motyka 1995.