Vulcan's Treasure-trove
"Vulcan's Treasure-trove"* is an Earthcache designed to introduce you to spectacular examples of local volcanic rock and help you identify various forms such rock can take. (Watch for other local rock formations, too!) In addition to exploring Dane Park for rock samples in their natural setting, you will be required to do a little outside research, easily done online and by using information included here.
The posted coordinates take you to one of Dane Park's entrances. Finding an entrance to the park is half the battle, so you're well on your way! At this entrance, you will find a paved path that soon branches in various directions. Your task will be to follow whichever path you feel inspired to take and, from that point, begin searching for the required rock formations (most are marked with descriptive plaques for your education and easement). Also note, the park itself is relatively small (17.3 acres), so you will never be far from a new discovery (or a park entrance/exit).
But first, before you set out… a little something about volcanoes!
Volcano
Magma,
Melted, molten rock,
Like soup that boils,
In a crock…
more
Volcanoes
A volcano, generally found where tectonic plates merge and converge, is an opening in the earth's surface or crust which allows escape for molten rock, pyroclastic debris (particles of volcanic rock of difference sizes; see chart in glossary) and gases. The illustration above offers a graphic representation of a volcano's anatomy.
For an interesting slide presentation about volcanoes, with some animation and a sound clip, click here. Warning! Before pressing the sound button on the audio slide, turn down and then adjust your speaker volume.
Some Ancient History: Avalon
By now, you may be wondering where the volcano is! Most of us usually think of volcanoes in the present tense or, if we think about volcanoes no longer active, we perceive they were active in 'recent' recorded history. But what we see in Dane Park goes back more than a bit further than that and actually started off the coast of Africa nearly 600 million years ago. In fact, New England's odd and curious geology is more similar to parts of Europe than to the rest of the US. How is that? Here is a little summary of the rocks' epic journey:
Once located in the Southern Hemisphere and part of the ancient African coast, a volcanic island chain (Avalonia) rifted from its African base. While Avalonia was located off the coast (some six hundred million years ago), the rocks of the Boston Basin** formed upon it. Avalonia (along with the landmass Baltica, later to become parts of Europe) then drifted northward across what was then the Iapetus Ocean, the two softly bumping each other along the way, both eventually colliding with the small continent Laurentia (located at the equator). This collision caused a major mountain-building event and Laurentia became Laurussia, later forming Pangaea after it collided with Gondwana (from which Avalonia rifted in the first place). Whew! The eventual rifting of Pangaea produced the Atlantic Ocean. At that same time, the Boston Basin, a small part of what became the Southeastern New England Avalon Zone (other parts of Avalonia ending up elsewhere), found its home on the coast of eastern North America.
So what is all this saying about the volcanic rock in Dane Park? Optional question below!
Hope you enjoy your journey!
Glossary
BASALT - a type of fine-grained, dark-colored extrusive igneous rock.
GABBRO - a type of coarse-grained (compared to extrusive igneous rock), dark-colored, intrusive igneous rock.
LAPILLI ("little stones" in Latin) – Size classification of pyroclastic debris, i.e., 2mm - 64mm. (See tephra/pyroclastic terminology chart below.)
IGNEOUS ROCK – Formed by the cooling of magma or the accumulation of materials ejected from volcanoes. Intrusive igneous rocks cool slowly within the Earth while extrusive igneous rocks cool when erupted onto Earth’s surface.
LAVA - (you will need to research this one)
MAGMA - (you will need to research this one, too)
MINERAL – A naturally occurring, non-living crystalline solid with a defined chemical composition and defined physical properties.
ROCK – Composed of minerals and classified into three groups (igneous, metamorphic, and sedimentary) based on their formation and composition.
TEPHRA PARTICLE SIZE CLASSIFICATION -
Logging Requirements
Note: Please do not post answers in logs. Please send your answers in a private message. If mobility is a problem, answer all questions that apply to paved trails and substitute question 9 for the one other question that requires navigating a secondary trail. PLEASE AVOID SPOILERS IN YOUR LOGS AND PHOTOS.
1. What is "lapilli ash" and what does it look like in the example seen in Dane Park?
2. In your own words, what is "gabbro magma"?
3. What is the difference between "magma" and "lava"?
4. What is the difference between "lava pillows" and "lava bombs"? What does each look like?
5. True or false. Roxbury Puddingstone can be found in Dane Park. If true, where did you find an example (give coordinates)? If false, why do you think there is none?
6. What is "basalt"? Where in the park do you find the large outcropping of "basalt" (marked with an informational plaque)? Give coordinates.
7. Find the rock pictured below; (it can be seen along the paved trail). How wide is it (longest horizontal measurement)? What kind of rock do you think this is? How do you think it got there?
8. (Optional) Post a photo of yourself, your GPS and/or your alter ego near your favorite volcanic specimen but make sure not to include any spoilers (such as an informational sign or other answers to questions). Why is this your favorite?
9. (Optional) How are Avalon (geological Avalon!) and the volcanic rocks found in Dane Park related?
10. (Optional) What, if anything, from this experience deepened your understanding of and appreciation for volcanic rock specifically and local geology generally?
P.S. There are other caches in the park!
Notes and References
*Vulcan: mythological god of fire, including the fire of volcanoes. Treasure-trove: literally "treasure that has been found."
**The rocks inside the Boston Basin include members of the Cambridge Formation (Cambridge Argillite), Roxbury Formation (Roxbury Puddingstone) and Brighton volcanics (lava and volcanic ash). More information about and examples of Roxbury Puddingstone and Cambridge Argillite can be found by exploring these other local Earthcaches: GC3ECHC, GC3EJ64, GCDEMV and GC2VJW8.
Poem:
Mr. R's World of Math and Science http://sciencepoems.net/sciencepoems/volcano.aspx
Photos and illustrations:
Foragess, Photo Dane Park rock formation
Town of Brookline, Photo Dane Park entrance http://www.brooklinema.gov/index.php?option=com_content&view=article&id=752%3Apaos-pp-dane-park&catid=647%3Apaos-park-pages&Itemid=965
Enchanted Learning, Volcano Illustration http://www.enchantedlearning.com/subjects/volcano/
Volcanoes:
Geology.com - http://geology.com/
Enchanted Learning, http://www.enchantedlearning.com/subjects/volcano/
J.R. Blueford, Ph.D. and Doris Raia, Volcanoes (slide presentation), http://msnucleus.org/membership/slideshows/volcano.swf Individual Wikipedia pages.
Avalon and the Boston Basin:
Dr. George Ehrenfried, "The Old Land of Cambridge," Distributed by the Cambridge Conservation Commission, April 1991
Foragess, Plums in the Pudding I: Mission Hill (earthcache) http://www.geocaching.com/seek/cache_details.aspx?guid=e3672e68-82c5-4904-8d62-31709b2f90d4
Glossary:
Museum of Science rock garden exhibit and publication: http://www.mos.org/media/docs/MOS_Rock_Garden_Map.pdf
bostongeology.com
Geology.com - http://geology.com/rocks/igneous-rocks.shtml
Carefully reviewed individual Wikipedia pages.
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Congratulations to gw0143 for being FTF (first to meet logging requirements)!