Mount Champlain EarthCache

The posted coordinates of this earthcache will bring you to the summit of Mount Champlain on Isle au Haut where you will learn more about the formation of the island, the mountain, and the type of rock it is made up of.  Bicycles are allowed on the island but not on hiking trails.  If there is snow on the ground, it won't be possible to complete this earthcache.

To log this earthcache as found:

• Read the cache page below to learn more about plutonic rocks
• Visit the earthcache site to explore the area
• Send me the answers to the questions at the bottom of the cache description section
• Post a photo of yourself and/or a personal item in front of the summit cairn 

ISLE AU HAUT

Isle au Haut is an island approximately 6 miles long by 2 miles wide in Penobscot Bay, part of the Gulf of Maine and Atlantic Ocean.  Mount Champlain, elevation 540 feet, is the highest point on the island, located on a north-south ridge occupying the island's center.

Isle au Haut is classified as Type III plutons. These are represented by granite, granodiorite, alkali-feldspar granite, and quartz monzonite and generally represented by an assemblage of associated magmas referred to as an igneous complex. Igneous is rock formed by solidification from a molten state.

MOUNT CHAMPLAIN

Mount Champlain is composed of a large mass of granite that has weathered to the surface over time. Its granite core formed within a cooled magma chamber below the earth's surface. When molten magma reaches the surface, it may extrude and flow as lava or violently eject outward under tremendous pressure.  Mount Champlain and the surrounding northern part of the island show signs that the lava flowed whereas in the southern part of the island there are signs of welded tuff which indicate that the lava violently ejected outward. 

The volcanic events are the result of tectonic plate convergence on the earth's surface, a process that forms continents, closes intervening ocean basins and builds mountain ranges. Mount Champlain was created during the plate collisions and mountain-building events of the early Paleozoic era that began raising the Appalachian Mountains.

Type III pluton development is often associated with strike-slip fault zones above slab break-off areas formed during episodes of tectonic plate convergence. The outer part of the earth, consisting of the crust and upper mantle (i.e., lithosphere), is predominantly affected by the formation of a slab window resulting in increased heating of the base of the upper lithosphere.  Also in this case, the uprising magmas are weakening the mantle and the lower crust, which results in strain localization during shearing along the uprising plutons

WHAT ARE PLUTONS?

Plutons are a body of igneous rock formed beneath the surface of the earth by consolidation of melted rock called magma.  A pluton exposed at the Earth's surface has had its overlying rock removed by erosion.  It represents the deep part of a magma chamber that once fed magma to a long-vanished volcano.

There are different shapes to plutons which provide geologists with clues on the origin of the rock.  Some shapes of plutons are:

• Bysmalith: A flat or rounded pluton that forms when magma rises into the earth's crust but doesn't erupt.  
• Diapir: A dome rock formation where a core of rock has moved upward and pierced through the earth's crust.  
• Laccolith: A blister-shaped pluton that raised the overlying rocks into a dome.
• Lopolith: Magma that spilled downward and created a depressed area.  It is similar to laccolith but concave down.  

HOW DO PLUTONS FORM?

Magma is less dense than rock and tends to rise as buoyant bodies called diapirs.  They are a deep-seated intrusion that made its way into pre-existing rocks in a melted form several kilometers underground in the Earth's crust and then solidified. At that depth, the magma cooled and crystallized very slowly, allowing the mineral grains to grow large and tightly interlocked — typical of plutonic rocks.

Plutons may readily melt their way upward in the lower crust, but they have a hard time reaching the surface through the cold, strong upper crust. It appears that they need help from regional tectonics that pulls the crust apart. Thus plutons are typically found in areas where one edge of the crustal plate is forced below the edge of another. 

PLUTONIC ROCK GLOSSARY

Rock	Description	Image
Diorite	Diorite is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar (typically andesine), biotite, hornblende, and/or pyroxene. The chemical composition of diorite is intermediate, between that of mafic gabbro and felsic granite. Diorite is usually grey in color with speckles of white.
Granite	Granite is a coarse-grained intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase.  It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies underground. It is common in the continental crust of Earth, where it is found in igneous intrusions.
Granodiorite	Granodiorite is a plutonic igneous rock, formed by intrusion of silica-rich magma, which cools in batholiths or stocks below the Earth's surface. It is usually only exposed at the surface after uplift and erosion have occurred. It is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar.
Quartz monzonite	Quartz monzonite or adamellite is an intrusive, felsic, igneous rock that has an approximately equal proportion of orthoclase and plagioclase feldspars. It is typically a light colored phaneritic (coarse-grained) to porphyritic granitic rock.

PLUTONIC ROCK MINERAL CONTENT

EARTHCACHE QUESTIONS

1. How was Mount Champlain formed? 
2. What is the approximate longest length of the exposed plutonic rock on the summit?  The easiest way to estimate the length is to measure your stride or foot length and then pace off the length.
3. Why is the plutonic rock on the summit exposed?   
4. What is the name of the shape of the plutonic rock on Mount Champlain? 
5. How did the plutonic rock get that shape?
6. Observe the rock you are standing on at the posted coordinates.  What type of plutonic rock is it?  Explain why.
7. List the minerals you observe in the rock along with the approximate percentage of each of them.
8. Post a photo of yourself and/or a personal item in front of the summit cairn.