Big Four Ice Caves
The Big Four ice cave trail #723 has several opportunities to view geology. For the first .03 of a mile you walk on boardwalks over a montane wetland, meaning a highland wetland that is below the tree line. In physical geography, a wetland is an environment "at the interface between truly terrestrial ecosystems and aquatic systems making them inherently different from each other yet highly dependent on both" (Mitsch & Gosselink, 1986). In essence, wetlands are transition area between two adjacent ecological communities.
At about .04 you arrive at the South Fork of the Stillaguamish River. When the water is low you can see the bedload of boulders, which are moved downstream during high water and flood conditions. Just a bit further, a bridge crosses over a tributary stream where the bedload of boulders are bigger yet, even though the stream is much smaller. Streams flowing down steeper slopes have higher velocities, and thus more energy to move larger size sediments.
As the trail starts to rise from the valley, you will see clays with fine layering and lack of pebbles and boulders of till deposits that make them lake deposits. There are 2 theories about how this lake formed. The first is that a large landslide downstream working as a dam, blocked the flow of the South Stillaguamish. The second is that the Puget Lobe of the Cordilleran Ice Sheet pushing up the Stillaguamish Valley from the Puget Lowland.
After hiking 1 mile you will see what you came for.. The Big Four Ice Caves! The ice caves are not glaciers but rather a debris field. During the winter months, huge snow avalanches fall down a vertical 4,000 foot rock wall of the Big Four Mountain to accumulate at the base of the slope. Much more snow builds up in the winter than melts in the summer, so the deposits at the base are under constant pressure from the weight of the snow above causing metamorphic recrystallization from snow to ice. This is a similar process forming glacial ice, except the Big Four ice does not flow downslope. Instead during the summer months most of the overlying snow disappears and meltwater streams cut a pathway through the base of the ice. These tunnels are enlarged by warm air flowing through, at the end of the summer they are tens of feet high and wide. The ice caves provide a natural air conditioning system as meltwater and cold air flow through them. The cool downdrafts minimize vegetation on the rocky plateau and allow subalpine wildflowers to grow at an unusually low altitude. The ice walls show a characteristic blue color caused by the fact that ice molecules absorb all of the frequencies of sunlight except the blue band, which escapes to reach your eyes.
To log this cache please provide a current photo of yourself at the caves, (will take foreheads if you can’t get your face in the shot if you are caching alone) also email me why the caves are extremely dangerous to enter. (hint it has to do with how they are formed). Sign can be found here N 48 03.391 W 121 31.089. Don't wait for for a confirmation email from me to log this cache. Go ahead and log (with your photo posted), but if I don't receive your email in one week I will have to delete your log. Earthcaches have a unique set of guidelines for the cache write up, and logging that must be met. Most importantly have fun!!
Sources: Hiking Washington’s Geology by Scott Babcock and Bob Carson
Wikipedia Ice Cave
Wikipedia Big Four Ice Caves
Glacier National Park
Congrats Logbear on FTF!! He gets and A+!