Please note - there is NO guaranteed cell phone reception at this cache site. Know the requirements for this earthcache before arriving.
Important things to know to avoid log deletion:
- if your answers will be sent at a later time, state when I will receive them in your found log.
- required photo must be personalized in some way so that I know you were truly there.
If I delete your found log due to lack of following instructions, you can re-log your find when you are able to comply.
This entrance to Mount Rainier National Park is generally open from about mid-June to mid-September. There is an entrance fee, good for 7 days, for each vehicle entering the entire park unless you have a special pass such as an annual pass or a Golden Eagle Pass. Information about these passes can be obtained at the entry points to the park. Please park only in designated parking spots and do not leave the trails/sidewalks during your explorations.
This is an earthcache, and as such, there is no physical container at the stated coordinates. Instead, there are questions to be answered to "find" this cache.
A few notes:
- a pass or fee is required to visit Mount Rainier National Park - more information may be found at Fees & Passes - Mount Rainier National Park.
- remember to stay on maintained trails at all times for the protection of the fragile subalpine meadows.
Equipment needed for this earthcache:
- binoculars
- a copy of the text and the questions to be answered
Why are there glaciers on Mount Rainier?
A glacier forms wherever snowfall repeatedly exceeds melting over a period of years. Above 6,500-7,000 feet on Mount Rainier, more than 50 feet of snow falls each winter, and not all of it melts before the next winter. The survival of this snow from one year to the next depends both on the cooler temperatures at the higher altitudes, and on the depth of the snowfalls there. If these same conditions exist in flat areas such as Antarctica and Greenland, ice caps or ice sheets rather than glaciers will be formed.
From Sunrise
How is glacial ice formed?
When temperatures remain below freezing following a snowfall, the accumulation of fluffy snowflakes soon changes. As air moves in the spaces between the flakes, their extremities evaporate, and the resulting water vapor condenses near the centers of the flakes. The snowflakes become smaller, thicker, and more spherical and air is forced out. What was once light and fluffy snow is recrystallized into a much denser mass of small grains having the consistency of coarse sand. This granular recrystallized snow is called firn.
As more snow is added, the pressure on the lower layers increases, compacting the ice grains at depth. Once the thickness exceeds 165 feet, the weight fuses firn into a solid mass of interlocking ice crystals. Glacial ice has now been formed.
The rate at which the transformation from firn to glacial ice occurs varies. In regions where the annual snow accumulation is great, burial is relatively rapid and snow may turn to glacial ice in a matter of a decade or less. Where the yearly addition of snow is less abundant, burial is slow and the transformation of snow to glacial ice may take hundreds of years.
Glaciers form when the amount of snowfall gained (in the accumulation zone) during a winter season surpasses the amount of snow that melts (in the ablation zone) in the warmer seasons. To be considered an official glacier, a body of ice must be moving. Signs of movement, which differentiate glaciers from ice sheets and ice caps, include things such as crevasses and ice flow lines.
How do glaciers move?
The movement of solid glacial ice is referred to as flow. There are two ways in which glacial ice flows.
The first is plastic flow, involving movement within the ice. Ice acts like a brittle solid until under the weight (pressure) of about 165 feet of ice above it. Once that load is surpassed, ice behaves as a plastic material, and internal plastic deformation begins. This causes slippage of ice layers within the glacier and the glacier moves downhill, moving like a deck of cards with the top layers moving more quickly than the bottom layers. Friction causes slower movement at the base and along other areas of the glacier coming into contact with solid objects.
A second and equally important mechanism of glacial movement is basal sliding, where the entire glacier moves as a single unit. Pressure at the base of the glacier decreases the melting point of water, and combined with geothermal heat from Earth's interior, a thin layer of meltwater is created, causing the entire ice mass to slip along the ground.
The 165 feet or so of a glacier in the uppermost zone moves only as a result of being carried along "piggyback" style by the ice below it. It is brittle and referred to as the zone of fracture. When the glacier moves over irregular terrain, the zone of fracture is subjected to tension, resulting in cracks called crevasses. Crevasses tend to form where the glacier flows over obstacles or around bends in valleys. They are no deeper than 100 to 165 feet as the ice pressure from the plastic flow seals them beneath that depth.
Glacial movement is not obvious, nor does all of the glacier move down valley at an equal rate. Friction with the bedrock floor and the valley walls slows down movement, so the flow is greatest in the center of the glacier. Some glaciers move so slowly that trees and other vegetation become established in the debris that has accumulated on the glacier's surface. Others may move at rates of up to several meters per day. Occasionally a glacier may suddenly speed up and advance large distances in a short period of time. This is known as surging.
Whether a glacier is advancing, retreating, or in balance, the ice within the glacier continues to flow forward and move down the slope due to the weight of the ice.
The glacial budget
Snow is the raw material from which glacial ice originates; therefore, glaciers form in areas when more snow falls in winter than melts in summer. Glaciers constantly gain ice due to accumulation and lose it as a result of ablation. The balance between the two, whether positive or negative, is referred to as the glacier mass balance.
All glaciers have accumulation and ablation zones. The boundary between these two zones, the equilibrium line, is the transition where accumulation equals ablation.
As explained above, the accumulation zone has three major layers. The top layer is the snow that thickens with each additional snowfall. The middle layer is the firn, a transitional form between the snow and solid ice below. The bottom layer is the glacial ice. The addition of snow thickens the glacier, making it heavier, and promoting glacial movement due to the pull of gravity.
Thickening of the glacier only happens high up on the glacier when there is increased accumulation. Then it will be a matter of years before that thickened section of the glacier flows its way down to the terminus. When that thickened part of the glacier reaches the terminus, it takes longer to melt, meaning that the glacier can slide and flow farther down the mountain before the melting is complete. As a result, the glacial terminus advances. The results of a heavy snow pack one year cause a net gain to the glacier, although that won't be evident at the toe of the glacier for five to ten years.
The ice of the ablation zone (zone of wastage) is covered with snow during winter. This snow melts completely in summer along with some of the glacial ice, causing a net loss to the glacier.
Whether the margin of a glacier is advancing, retreating, or remaining stationary depends on the budget of the glacier. The glacial budget is the balance, or lack of balance, between accumulation at the upper end of the glacier and ablation at the lower end.
When ice accumulation and ablation are equal and in balance, the terminus of the glacier is stationary. When there is more accumulation than ablation, the terminus advances over time and the glacier mass balance is said to be positive. When accumulation is less than ablation, the terminus retreats over time and the glacier mass balance is said to be negative.
What things affect glaciers?
Climate determines how much snow a glacier receives and how fast it melts. During a cold and wet year, glaciers will gain more snow than they lose, causing the glacier to advance over time. During warmer or drier years, more snow and ice melts than is formed, causing them to retreat. Changes in glacier size (accumulation/advance and ablation/retreat) depend on the climate including air temperature and snowfall.
Also affecting glacial change are the glacier's size, orientation, elevation and thickness. In general, glaciers that are smaller, or lower in elevation, or facing south, or less thick are more susceptible to changes in climate.
Carbon Glacier is the lowest-elevation glacier on Mount Rainier and in the contiguous United States. However, it is also the thickest at 700 feet, the longest at 5.7 miles, and has the greatest volume at 0.2 cubic miles. As a result it has exhibited the least amount of retreat/ablation of all the glaciers on the mountain.
Another determination is rock/debris cover. In 1963, Emmons Glacier experienced a rockfall from Little Tahoma Peak. This debris now insulates the ablation zone from sun and warmth, reducing melting, lessening the retreat of this glacier. Close up, glaciers can look very dirty as a result of rockfalls and other debris and sediments. Moraines form at the terminus of glaciers where the rock and debris are dropped as the toe melts.
Over the last century all Mount Rainer glaciers have retreated significantly. While the response of each glacier depends on its local conditions, currently overall glacier loss seems to be largely the result of a regional tendency toward warmer weather, resulting in less snowfall and higher rates of ablation. The recent retreat of the Mount Rainier glaciers during the late 1980's and the 1990's is primarily caused by warmer than average summer temperatures and drier winters. Prior to the late 1980's the glaciers were advancing because of wetter winters and cooler summers. These two factors are the primary driving force behind glacier changes.
Glaciers are very accurate climate thermometers; they respond to changes in climate over time. The fact that all of our nearby glaciers are retreating is clear and irrefutable evidence that local climate is warming. The fact that this pattern is happening by and large all over the world is clear evidence that global climate is experiencing a warming trend. For more information about climate changes, start by looking up Pacific Multidecadal Oscillation.
Some trivia
- there are 25 named glaciers on Mount Rainier.
- Mount Rainier has the largest number of glaciers on a single peak in the contiguous United States.
- five glaciers start at the summit: Emmons, Nisqually, Winthrop, Tahoma and Ingraham.
- Carbon Glacier is the longest (5.7 miles) and the thickest (700 feet) and its terminus is the lowest (3,500 feet) of any glacier in the United States.
- Emmons Glacier has the largest surface area (4.3 square miles) of any glacier in the contiguous United States.
- Nisqually Glacier has the fastest measured movement downhill (29 inches a day) for a Mount Rainier glacier.
How to claim a find for this earthcache:
To get credit for this earthcache, send the answers to the questions to me. Please log your find as soon as you send answers - do not wait for my response. I will contact you promptly with approval or let you know if I need additional information from you. I may also send additional information to you if appropriate. If answers are not received in a timely manner, found logs will be deleted. Cut and paste the following into your response with the answers, preferably through the message center. (My responses to you will be sent through the message center.)
Cut, paste, and add the answers using both the text and your observations:
Glaciers Anatomy and Physiology earthcache questions: (Please use the cache description in conjunction with your observations in order to answer questions correctly.)
1: For which cache are you sending answers? (if you click on the CO name on the cache page to go to the message center, this will be automatic)
2. What three things are necessary for alpine glaciers (mountain glaciers as opposed to continental glaciers) to form?
3. Which two of the three things in #2 determine glacial accumulation and ablation?
4. What are the three layers of a glacier in the accumulation zone?
5. Name 6 things that can affect the accumulation/advance or ablation/retreat of a glacier.
6. Emmons Glacier is 3.9 miles long. If it theoretically were to move at the rate of 1 foot a day and there is a heavy snowpack in 2020, when would you anticipate seeing an advance of the glacier's terminus?
7. Using your binoculars, look at the glacier. What do you see other than white snow? Rockfall? Crevasses? Plant growth?
8. Required to keep your found log in place - a photo of you (name tag or name on a piece of paper accepted) at the cache coordinates posted with your found log.
Sources:
Essentials of Geology - Lutgens, Tarbuck & Tasa
USGS publications