On site you find information about the Trans-Alaska Pipeline System (TAPS) and Permafrost.
Permafrost
Permafrost is soil, rock or sediment that is frozen for more than two consecutive years. In areas not overlain by ice, it exists beneath a layer of soil, rock or sediment, which freezes and thaws annually and is called the "active layer".
This means that permafrost occurs at an annual temperature of 28.4 °F or colder. Active layer thickness varies with the season, but is 0.3 to 4 meters thick.
The extent of permafrost varies with the climate:
In the Northern Hemisphere today, 24% of the ice-free land area, equivalent to 19 million square kilometers, is more or less influenced by permafrost. Of this area slightly more than half is underlain by continuous permafrost, around 20 percent by discontinuous permafrost, and a little less than 30 percent by sporadic permafrost. Beneath the active layer annual temperature swings of permafrost become smaller with depth. The deepest depth of permafrost occurs where geothermal heat maintains a temperature above freezing.
Discontinuous permafrost
Typically, the below-ground temperature varies less from season to season than the air temperature, with mean annual temperatures tending to increase with depth as a result of the geothermal crustal gradient. Thus, if the mean annual air temperature is only slightly below 32 °F, permafrost will form only in spots that are sheltered—usually with a northerly aspect—creating discontinuous permafrost. Usually, permafrost will remain discontinuous in a climate where the mean annual soil surface temperature is between − 23 and 32 °F. Exceptions occur in un-glaciated Siberia and Alaska where the present depth of permafrost is a relic of climatic conditions during glacial ages where winters were up to 20 °F colder than those of today.
Continuous permafrost
At mean annual soil surface temperatures below 23 °F the influence of aspect can never be sufficient to thaw permafrost and a zone of continuous permafrost forms. A line of continuous permafrost in the Northern Hemisphere represents the most southerly border where land is covered by continuous permafrost or glacial ice. The line of continuous permafrost varies around the world northward or southward due to regional climatic changes.
Thaw
The ground can consist of many substrate materials, including bedrock, sediment, organic matter, water or ice. Frozen ground is that which is below the freezing point of water, whether or not water is present in the substrate. Ground ice is not always present, as may be the case with nonporous bedrock, but it frequently occurs and may be present in amounts exceeding the potential hydraulic saturation of the thawed substrate.
By definition, permafrost is ground that remains frozen for two or more years. Since frozen soil, including permafrost, comprises a large percentage of substrate materials other than ice, it thaws rather than melts even as any ice content melts. An analogy is when a freezer door is left open, although the ice in the freezer may change phase to a liquid, the food solids will not experience a phase change. In aggregate, the food thaws but does not melt. Melting implies the phase change of all solids to liquid. One visible sign of permafrost degradation is the random displacement of trees from their vertical orientation in permafrost areas.
Trans-Alaska Pipeline System
The Trans-Alaska Pipeline System (TAPS) includes 11 pump stations, several hundred miles of pipelines, and the Valdez Marine Terminal. TAPS is one of the world's largest pipeline systems.
The pipeline was built between 1974 and 1977, after the 1973 oil crisis caused a sharp rise in oil prices in the United States. This rise made exploration of the Prudhoe Bay oil field economically feasible.
In building the pipeline, engineers faced a wide range of difficulties, stemming mainly from the extreme cold and the difficult, isolated terrain. The construction of the pipeline was one of the first large-scale projects to deal with problems caused by permafrost, and special construction techniques had to be developed to cope with the frozen ground. The pipeline is capable of delivering over 2 million barrels of oil per day but nowadays usually operates at a fraction of maximum capacity. If flow were to stop or throughput were too little, the line could freeze.
This is an EarthCache - without a container or logbook - where you'll document your observations and understanding via email to earn credit for this cache.
Log condition:
Any cacher visiting an EarthCache and answering the tasks via email or message center can immediately log this EarthCache. The EarthCache Guidelines deliberately do not intend to wait for a log release from the owner. Who answers later has the possibility of a "write note".
To complete this earthcache, e-mail the answers of the following questions to cache.baer.
Don't put answers to the questions in your online log!
1. What is permafrost?
2. Where do we find permafrost?
On site you will find further information on how to prevent thawing of the permafrost soil.
3. Special construction techniques where developed to cope with the frozen ground. Which construction is used?
4. Why is it importand to elevate the pipeline in permafrost areas?
5. Add a photo to your log showing you or a note with your geocaching name on the Earthcache (this is a condition for logging the cache, see Earthcache Guidelines §6).
References:
https://en.wikipedia.org/wiki/Permafrost
https://en.wikipedia.org/wiki/Trans-Alaska_Pipeline_System