There is no physical cache container to find; to log this EarthCache, you will need to message or email us the answers to the five questions below (see Logging Requirements in the text below).
The upper portion of Mount Washington above 5200 feet is known as "The Rock Pile" because of the felsenmeer (German for "sea of rocks") on the upper reaches of the mountain. Standing at the cache coordinates and looking towards the actual summit you can see why the summit has been given that name. You would see it even more dramatically as you made your way up whether you hiked up, or drove up, or took the Cog Railway up to the summit.
The White Mountain landscape was impacted by a few types of glacial action, continental ice sheet and alpine glaciers, as well as weathering:
Impact: Continental Ice Sheet
The continental Pleistocene "Ice Age" glaciers impacted the mountain with the most recent one being the Laurentide Ice Sheet which started as smaller ice sheets in Canada that expanded and merged to make one large continental ice sheet covering much of Canada and part of the northern United States. The ice sheet spread across New England about 30,000 years ago and withdrew from the White Mountains completely about 13,000 or so years ago. The glacier acted like a giant machine that eroded and pulverized large amounts of rock and carried what it had captured for miles. The ice sheets had tremendous weight and tended to scour the bedrock as they moved over it removing loose rocks and sediments that had formed over millions of years of erosion from the weather and water. Glaciers would sweep up anything that was loose and as the glacier moved the rocks embedded in it would scar bedrock and other rocks over which it passed leaving behind striations or a series of parallel marks to show the direction the glacier was moving at that location. A glacier moving directly south would leave striations oriented north and south at that point. In the White Mountains valleys that are U shaped indicated that the glacier moved through that valley like Crawford or Franconia Notch.
Rocks carried by the glacier and then left behind once the glacier retreated are known as erratics if they are big enough and are left somewhat randomly. Collections of smaller rocks and gravel can be moraines at the end of a glacial lobe and there can be eskers which can look like rock snakes that are left as a glacial retreats and smaller rocks and pebbles are left by a stream under the glacier.
Impact: Alpine Glaciers
The second type of glacier impacting the mountain were alpine glaciers during periods when the large ice sheets were not in place. Alpine glaciers created large rock-walled basins known as cirques that were created by alpine glacier erosion. Tuckerman Ravine which is on the south side of the summit is one of these cirques along with Huntington Ravine, Franklin Gulf, and Oakes Gulf among others. None of these cirques retained active glacial ice following the continental glaciation but the ice in them was still able to sculpt the cirques while they were active.
Impact: Weathering
Weathering has also had an impact on the White Mountains with different rock types weathering at different rates with metamorphic rocks taking longer to weather than the granite igneous rocks.
What Happened When?
On the summit of Mount Washington cosmogenic nuclide exposure dating (which looks at isotopes in the rocks to date them) showed dates roughly around 14,000 years for some granitic rocks which one would expect if the summit had been overrun by the Laurentide Ice Sheet and some traveling rocks from the northwest were dropped off. However other boulders on the summit showed ages in the range of 30,000 years to 120,000 years suggesting that they had been in place and had been weathered for a much longer period, from before the last ice sheet. At lower elevations below 5200 feet the exposure age of boulders was in the 12,000 to 16,000 years old which also would suggest they were deposited at the same time the ice sheet started to retreat leaving the rocks behind.
Why Are Weathered and Less Weathered Rocks Mixed Together?
That begs the question of why does the summit have a majority of older weathered rocks along with a scattering of less weathered rocks among them if the ice sheet covered Mount Washington. Wouldn't the ice sheet have scraped all the old loose boulders away and then left behind only the newer less weathered rocks?
There are a number of theories to explain why there is such a strange mix of differing weathered and aged rocks on the summit:
Theory A) The earliest researchers proposed that there was no glaciation above 5200 feet or very light glaciation above 5200 feet which left existing weathered rocks in place.
Theory B) Goldthwait and Thompson disagreed with Theory A and suggested that the features were a result of the harsh climate that followed glaciation with much worse weathering below 5200 feet than above.
Theory C) Fowler suggests that it doesn't explain why 5200 feet would be such a clear dividing line in climate impact and it doesn't explain why lightly weathered granitic erratics coexist with the much more weathered metamorphic boulders. since they both would have been exposed to the same weather since the last ice sheet. In fact the granite of the erratics typically weathers much more quickly than the metamorphic boulders. Fowler's theory is that at the onset of the last glaciation the existing boulder field was infiltrated by precipitation which froze forming a solid frozen layer that was then overridden by the locally thin Laurentide Ice Sheet above 5200 feet. The ice sheet would not have removed the existing boulder field but the granitic erratics brought from the northwest would have been deposited among the heavily weathered rocks of the existing boulder field.
Logging Requirements
To log this earthcache, message or email us and copy and paste these questions, along with your answers. Please do not post the answers in your log, even if encrypted. There's no need to wait for confirmation from us before you log, but we will email you back if you include your email address in the message. Group answers are fine; just let us know who was with you.
- How long ago in years did the continental ice sheet withdraw from the Mount Washington area?
- What was the age range for the boulders below 5200 feet elevation?
- What were the two ages of the boulders found on the summit?
- From where you stand at the GZ walk around a bit and look closely at the rocks between you and the summit. Are the rocks all roughly weathered the same or can you see some more weathered than others?
- Which of the three theories in the text above (Theory A, Theory B, or Theory C) do you think best explains why the summit has a mixture of old and new rocks with varied weathering and why do you think that theory makes the most sense?
If you would like please take a picture of a portion of the "The Rock Pile" and attach to your log, but a picture isn't required to log a find.
Note that you can hike up for free to find the EarthCache or, depending upon the time of the year, pay to take the cog railway up or come up the auto road.
A lot of the information for this cache was taken from the excellent and fascinating book "The Geology of New Hampshire's White Mountains",Eusden,Thompson,Fowler,Davis,Bothner,Boisvert, Creasy. 2013 Durand Press.