Sunday, December 8, 2013

The Outcrop in the Crystal

It's my 20th post!  This blog post is the first of several that will highlight an outcrop that drove my interest in Maine geology.  If you're looking for the outcrop it's on Rte. 115 on the Gray/ Windham border.  Or check it out on the Sphere app.  

The outcrop told the story of Maine.  The white rock, a granite, bubbled up when Africa's coast collided with our own 450 million years ago, sealing Maine into the Pangeaic interior.  The black basalt resulted from one of the volcanoes that once again cleaved the supercontinent in two when Pangea split.  The glittery schist told the tale of a muddy ocean bottom that predated both two igneous rocks.  But how did the green rock get there?

There were obvious clues.  The parallel stripes of white, green, and sometimes even gray told tales of piling layers.  The fact that these layers took turns with schist, a mudstone altered by heat and pressure, as one scanned the outcrop from left to right suggested that it, too, formed in that muddy sea.  Other facts didn't add up.  The tough rock scored glass.  Most of the usual sedimentary suspects wouldn't do that; unmetamorphosed mudstone and limestone were just too soft.  Their metamorphic progeny, schist and marble would have crumbled as well.  Sandstone, and its postbear quartzite, would do the job, but the look wasn't right.  The rock lacked the granularity of sandstone, and the sugariness of quartzite.

The truth became clearer as I began to research Silurian time, a period between 416 and 444 million years ago, in which the green rock formed.  The ocean bottom that it gathered in was flanked on three sides.  To the north lie North America, to the south, a hunk of land that would become Maine's coast. To the east, Western Europe plugged another opening preventing the flow of currents.  The phlegmatic basin, just south of the equator, became poor in oxygen, but rich in life.  Lacking our usual breath of life, the creatures of the sea resorted to extreme measures - consuming sulfur.  

The chemistry of this bounded sea played an important role in the green rock's formation.  As a coral reef, in an aerated ocean, degrades, it forms limestone, which is composed of the elements calcium, carbon and oxygen.  Our sluggish sea would have produced a similar product, with one small difference: the sulfur consumption exchanges some of the sediment's calcium for a new element - magnesium.  The rock it forms goes by a different name: dolomite.

Even dolomite doesn't have the strength to scratch glass.  The rock would require one final transformation.  As plates moved, the basin grew smaller, and then disappeared.  The formation of Pangea spurred an influx of fluids: some large, like the bulb of magma that formed the white granite, some less immense, like the infusion of quartz and water that flowed through the ancient ocean bottom.  This liquid sought out any channel it could access, including spaces in the schist, and the dolomite.  The schist proved passable, but inert.  The dolomite was reactive.  The heat and chemicals in the flowing fluid released carbon and oxygen from the dolomite (as carbon dioxide).  Some of the quartz stuck around, providing the white layers of the rock.  The green crystals, a mineral called diopside, kept the calcium and magnesium of the dolomite and replaced the CO2 with silicon and oxygen from the quartz.  

The outcrop is a testament of Maine's geological history.  It documented the marine roots and the accordion push-pull of continents.  The green diopside crystal, a fractal of that outcrop, records the deoxygenated ocean bottom in its calcium and magnesium.  It further tells the tale of the pushing and pulling continents in its silicon and oxygen.  The green crystal, a mere fragment of the outcrop, tells the outcrop's entire story.

Bickle, M. J. , H. J. Chapman, J. M. Ferry, D. Rumble, and A. E. Fallick. "Fluid Flow and Diffusion in the Waterville Limestone, South—Central Maine: Constraints from Strontium, Oxygen and Carbon Isotope Profiles." Journal of Petrology 38.11 (1997): 1489-1512. Print.

Ferry, J. M.. "A Comparative Geochemical Study Of Pelitic Schists And Metamorphosed Carbonate Rocks From South-central Maine, USA." Contributions to Mineralogy and Petrology 80.1 (1982): 59-72. Print.

Fischer, Dan , Tammy (Yue) Liu, Emily Yip, and Korsen Yu. "The Silurian Period."The Silurian Period. University of California Museum of Paleontology, 5 July 2011. Web. 6 Dec. 2013. <http://www.ucmp.berkeley.edu/silurian/silurian.php>.

Hussey, Arthur M., II, 1996, Bedrock geology of the North Windham 7.5' quadrangle, Maine; Maine Geological Survey (Department of Conservation), Open-File Report 96-16, 6 p.

Helmholtz Centre for Ocean Research Kiel (GEOMAR) (2012, June 7). How does dolomite form?. ScienceDaily. Retrieved December 8, 2013, from http://www.sciencedaily.com/releases/2012/06/120607105815.htm

Wilde, Pat , William Berry, and Mary Quinby-Hunt. "Silurian Oceanography."Marine Sciences Group. University of California, Berkeley, n.d. Web. 8 Dec. 2013. <http://www.marscigrp.org/sil91.html>.


Monday, November 11, 2013

Beyond Pangea: The Chain Lakes' Long History

Every middle schooler hears about Pangea.  You look at the world map and envision the ocean closing and that land before time re-forming.  And that's the end.  You don't think about what happened before because no one ever told you that there was a before.  Well, I am here to set you straight.

Don't get me wrong.  Pangea is old.  When Pangea was THE place to be, dinosaurs had not yet set foot on this Earth.  In fact, the dry center of the giant continent set the stage for water loving amphibians to evolve into drought tolerant reptiles.  Later, these reptiles gave birth to the generations that would become the feared lizards we call dinosaurs.  Here in Maine, however, you will find no trace of dinosaurs, because nearly every rock was formed before the oceans that collapsed to make way for Pangea produced their parting waves.

What's important to realize is that the formation of whole Earth continents, like Pangea, is a cycle.  These so-called supercontinents occur occasionally throughout Earth history.    Six hundred million years ago, the supercontinent of the day, one that we call Pannotia, would have filled much of the space taken up by the modern day western Pacific Ocean, and a large hunk of Antarctica, too.  About 1.3 billion years ago, Rodinia was gathering all the Earth's land masses at the equator.  This is the point at which we will begin our journey back to the future.

The Chain Lakes Massif, an elevated hunk of land just north of Sugarloaf, may be the best perch from which to watch the story unfold.  A supercontinent is formed when an ocean closes.  The weighty seafloor rock descends into the Earth beneath the lighter continental shoreline. The diving rock melts, and then reascends, forming a chain of volcanoes, not unlike the modern Andes.  The larger the colliding continents, the larger the mountain chain - and Rodinia was big!  The billion year old mountain chain is now the core of North America, running the 3000 miles from Newfoundland, Canada to Veracruz, Mexico.  Big mountains fall fast, and as rain and ice dragged sediment from the peaks it dropped it into the closing ocean.  Some scientists think it was this sediment that would become the Massif.  As the ocean closed, the sediment may have changed from mud to stone.

A billion years ago Rodinia was formed, but this, too, must pass.  The mega-continent shattered.  While the 3000 mile backbone, called the Grenville Province, stayed intact, the sedimentary shorelines drifted away.  While the cycle continued, the sedimentary island moved along the Earth's surface, but 400 million years after it started its journey, the Massif came home.  As its ocean closed, and Pannotia gathered, the piece of land that would become the Chain Lakes became nestled in the heart of the new supercontinent.  Nestled may be an understatement, because the crushing force of the continent forming squeezed, buried, and roasted the rock, altering it from a simple sedimentary rock to a banded metamorphic one called gneiss.

Pannotia didn't last long, and when the proto-Pangea split, the Massif hung on to what would become North America.  In fact at that time it would have been coastal property, but that would change as oceans closed one more time.  The Iapetus Ocean (Iapetus was the father of Atlas, and the Iapetus was the predecessor of the Atlantic) closed in stages.  The first impact was a set of Carribean-like islands, the next a small continent called Avalon.  Each collision provided more heat and more pressure, driving the gneissic metamorphism of the once sedimentary rock even further; and making the geologic puzzle harder to solve.

The final crunch came as Africa found its place in the Pangeaic landscape.  The world, different than the one in which we now reside, would at least be familiar to our geographic sensibilities.  South America cuddled up with western Africa, and northern Africa spooned by New England.  Pangea may be the first chapter in our middle school geology texts, but it was one of the last in this corner of Maine.

DiPietro, Joseph A. Landscape Evolution in the United States: An Introduction to the Geography, Geology, and Natural History. Burlington, MA: Elsevier, 2013. Print.

Landing, Ed. "Vestiges of Rodinia: Adirondack and Hudson Highlands." New York State Geological Survey. New York State Museum, n.d. Web. 11 Nov. 2013. <http://www.nysm.nysed.gov/nysgs/nygeology/tectonic/02.html>.

Meert, Joseph . "A History and Preview of Supercontinents through Time." Gondwana Research. N.p., n.d. Web. 11 Nov. 2013. <http://gondwanaresearch.com/hp/supercon.pdf>.

Monday, October 14, 2013

A Piece of Deer Isle: Rapakivi Fingerprints


When I first started learning about rocks I remember being impressed that each rock formation was unique.  The reddish color of a brownstone cobble in Finlayson, Minnesota informed me that the rock had made the 50 mile trip from the iron rich shores of Lake Superior.  I've started to look for fingerprints in rocks, and there is none more common in Maine than the rapakivi crystals of Deer Isle granite.
Deer Isle Stonework in Falmouth, Maine

While the formation has its home on its namesake island downeast, Deer Isle granite is everywhere.  You can hardly take a step in the L.L. Bean flagship store without resting your sole on a slab. I've noted its presence in kitchen counters, cutting boards, and outdoor stonework.  It even secreted itself into the foundation of Yankee Stadium, a long trip for a stone from Red Sox territory.  In any of these locations the rock would be instantly recognizable by its round pink crystals wrapped in a ring of white.


Close up of Deer Isle granite.  Notice the rounded pink crystal
in the center, and the white rim surrounding it.
The ring not only gives up the source location, it tells a story.  The pink mineral, microcline feldspar, is not normally round. When it developed deep under the surface it would have taken the form of a prismatic rod with regular angles. But this was under pressure.  Where the microcline first solidified may have been 10 miles under the surface. That means 10 miles of rock weight are pressing down on our magma stream like the grasp of Superman.  Just like the hero's clutch could turn coal into diamond, the added pressure that comes with this weight turned liquid rock into solid.  But the crystal had formed before its time.

As this slurry of magma and loose crystals rose up toward the surface, the weight pressing on it subsided.  Without the added pressure, the geometric crystals began to melt, leaving only their rounded centers behind. As the ooze ascended, crystal formation conditions changed.  The microcline, more stable in the deeper conditions, would now be replaced by a different mineral, white plagioclase feldspar.  Because the two minerals are very similar, the plagioclase quickly continues the pattern disrupted by the pressure drop.

Conditions must be just so to create this pattern. A cooler magma channel, the white mineral never forms.  The pressure drops too quickly and the pink feldspar melts altogether. Deer Isle granite's unmistakeable fingerprint is a result of its unique story of formation, dissolution, and restoration. This distinctness may be one trait that makes the stone desirable, but it is certainly one that makes it recognizable.

Eklund, O., and A.D. Shebanov. "The origin of rapakivi texture by sub-isothermal decompression." Precambrian Research 95.1-2 (1999): 129-146. Print.

Hooke, Roger Leb.. "A Geologic History of Deer Isle, Maine." College of the Atlantic, Serpentine Ecology Conference. July 2007. Web. 14 Oct. 2013. <www.coacommunity.net/downloads/serpentine08

Nekvasil, Hanna. "Ascent of Felsic Minerals and Formation of Rapakivi." American Mineralogist 76 (1991): 1279-1290. Print.

Prinz, Martin. Rocks and Minerals Simon & Schuster's Guide to Rocks and Minerals.. New York, NY: Simon and Schuster, 1978. Print.

Sunday, September 29, 2013

9 Stories from my Stone Pile

1. The Layers
The layers in this rock suggest that it accumulated over time as sediment piled up somewhere. In the case of this rock it most likely occurred at the bottom of an ocean.







2. The Metamorphosis 
The layered rock was exposed to intense heat and pressure. Though not hot enough to melt the rock the heat and pressure were sufficient to cause minerals to migrate through the solid rock toward one another. This migration fused microscopic clay particles into visible shards of mica pictured here.

3. The Mixing
The dark gray rock in the picture above has a composition similar to the rock above. When Africa collided with North America the magma that formed the white rock rose from below the ocean bottom. Hunks of ocean bottom floated in the molten rock like ice cubes as the liquid rock hardened into the light colored rock.

4. The Crystals 
As the light colored magma cooled, similar minerals were drawn toward one another. Because cooling happened deep underground minerals could move freely through the warm liquid. The pockets of quartz (clear), hornblende (black), and feldspar (white) grew larger and larger until they froze into solid crystals.

5. The Big Crystals 
As the mass of crystals from the picture above solidified, they may have shrunk or cracked leaving space for water and more magma to pulse through the spaces. The water allowed the crystals to grow even larger than regular granite, making a rock called pegmatite.

6. The Splitting

As we all know Pangaea was not a permanent fixture. When it split it was not a clean break. Many places in Maine cracked, creating fractures throughout the coastal region. These joints provided space for new rocks, like the black one above to get up close and personal with older rocks.






7. The Black Rock 
Earlier, I mentioned that the light colored magma came when Pangaea formed. Less dense granite tends to form when continents collide, while dark basalt, pictured above is a sign of splitting. As the two hunks of massive continent diverged, magma that formed through this black rock spilled through every crack it could find.  This dark rock is Pangaea's swan song. 

8. The Ice
Bedrock tends to break off at relatively sharp angles.  Streams tend to form rounded rocks.  These stones fall somewhere in the middle.  They have softened edges, but flat faces.  A mile of ice covered this spot several thousand years ago.  The glacier scraped every type of bedrock in Maine, plucking off chunks as it went.  The glacier broke away hard edges, and sanded off flat facets as rocks were dragged across the ground.

9.The Pile 
The glacier grabbed everything it could, from clay to boulders, and everything in between.  Farmers could plough through the small stuff, but these stones got in the way.  As the freeze-thaw cycle of Maine's weather brought stones to the surface, farmers fought back by flinging them to the edges of fields.  Here lie the remains of decades of farm labor and hundreds of millions of years of geologic history.









Sunday, September 15, 2013

Unfolding the Camden Hills


Two weeks ago my friend Colin and I climbed Mount Megunticook.  I was bending his ear about a particular rock, or piece of geologic history when he asked me the question: so how did the Camden Hills get here?  The question haunted me.  It's certainly a question I'd pondered.  I just hadn't made any headway.  I'd researched it too; the answers were either non-existent, or just didn't add up. Glaciers? But, ice sheets scoured the whole state.  Why leave peaks here?  Granite? There may be occasional injections of the light colored rock, but no more than other, lower regions of the state.  Over the intervening weeks I revisited both and decided that perhaps the answer lies in the the shattered infrastructure of the region.

I've mentioned in a previous post that this region was ground zero for a major collision between plates, and the impact is still visible on a relief map.  The ridges to the north and west of the Camden Hills look like ripples in a carpet pushed up by slid furniture.  If Africa was a couch, and Maine an area rug, this isn't too far from the truth.  When Pangea formed, Maine's rock needed to take up less space.  Like the carpet, part went up, and the rest stayed down.  The difference is, rock is not so good at bending.  Instead, a wedge of rock cracks off along a fault, and slides up the face of the piece next to it.  This crack-slide scenario occurred twice, with state geologic maps showing thrust faults not far from two ridges: one that includes Levenseller Mountain, Moody Mountain and Philbrick Mountain and another that features Hatchett Mountain and Coggans and Clarry Hills.

If collision shoves rock skyward, extension drops it down.  When Africa moonwalked its way out of Pangea, it stretched Maine behind it.  Certain blocks of Earth dropped down, filling would be holes with wedges of rock.  To the southeast of the Camden Hills, the land quickly plunges to ocean. The state maps once again show a fault and a cross section makes it look as though the fault block  descended with extending crust.

Where does this leave us?  Three hunks of rock stacked up piggy-back and a piece of ocean dropped into a hole left by a departing Africa.  The Camden Hills, with Megunticook the highest mountains on the Atlantic coast south of Acadia, are the top piggy with the drop to the ocean providing stunning views.  Of course, the once neat blocks have been intruded by magma, and worn down by glaciers and time.  But, I believe, these small giants, are more a tribute to the tug of war between continents than the ice and granite.

Bloom, Arthur. Geomorphology: A Systematic Analysis of Late Cenozoic Landforms. Upper Saddle River, New Jersey: Prentice Hall, 1991. Print.

"Facing Hatchet Mountain." Hope Historical Society. Hope Historical Society, n.d. Web. 15 Sept. 2013. <www.hopehist.com/Himages/HD402.html>.

Flanders . "Mount Megunticook : Climbing, Hiking & Mountaineering : SummitPost."Climbing, Hiking, Mountaineering : SummitPost. SummitPost.org, 12 Oct. 2013. Web. 15 Sept. 2006. <http://www.summitpost.org/mount-megunticook/234387>.

Osberg, Philip H., Hussey, Arthur M., II, and Boone, Gary M. (editors), 1985, Bedrock geologic map of Maine; Maine Geological Survey (Department of Conservation), scale 1:500,000

Saturday, August 31, 2013

The Ocean Bottom on the Mountain

Ernest Hemingway is rumored to have won a bet by telling the world's shortest story: "For Sale: Baby shoes, never worn."  As I sat on the side of Dorr Mountain, waxing geologically to my brother-in-law, he pointed out to me that the story I was telling was really much shorter than the words I was using.  Perhaps a shorter telling would have gone something like this: "Ocean bottom found on a mountaintop."

Hemingway's story was all about what it implied.  So what is implied by a four-foot boulder of ocean bottom rock?  Time.  Ignoring that this rock was part of a much larger formation, we can conclude that these four feet must have piled up over time.  One resource suggests that clay, likely once a major component of this chunk of sea floor, gathers at 10mm every thousand years.  This isn't a rock; this is a time lapse of 1.2 million years of arduously slow settling of clay.

So what about the mountain itself? The depths at which granite is formed are measured in miles (kilometers really, but this is America, right?).  That means that the bulb of granite that makes up most of Mount Desert Island once rested deep under the Earth's surface; now Dorr Mountain stands nearly a quarter mile above sea level.  Over the hundreds of millions of years since that deep magma cooled, wind, water and ice have excavated the remains of an ancient collision between North America and the ancient land mass on which MDI rests.

A look at the sea bottom rock implies something more. Several flat faces, on many planes, give evidence of glaciers. The glacier that plucked that rock from its original bed dragged the behemoth across the Earth's surface like cheese across a grater. The chaotic innards of the glacier occasionally flipped the mighty stone, smoothing yet another face.  The glacier, perhaps a mile tall, would have both ripped at Dorr, and been slowed by it. As the ice layed the mountain low, it may have slowed sufficiently to drop some of its load - seafloor included.

Hundreds of thousands of years of piling clay, miles of erosion, and an ice sheet a mile thick, all whispered in the language of rocks.  Scenes like this, like the glacier that came before them, cover Maine. Millions of shorts stories, implying so much more.


Ansley, J. E. 2000. The Teacher-Friendly Guide to the Geology of the Northeastern U.S. Paleontological Research Institution, Ithaca, NY.  

Hardcastle, Tim . "Pelagic clay ." Historical Geology- Wikibooks. Wikibooks, n.d. Web. 1 Sept. 2013. <http://en.wikibooks.org/wiki/Historical_Geology/

Miller, Robert B. , Scott R. Paterson, and Jennifer P. Matzel. "Plutonism at different crustal levels: Insights from the ~5–40 km (paleodepth) North Cascades crustal section, Washington." The Geological Society of America Special Paper 456 (2009)


Petford, N. , A. R. Cruden, K. J. W. McCaffrey, and J.-L. Vigneresse. "Granite magma formation, transport and emplacement in the Earth's crust." Nature408 (2000): 669-673. Print.

"Dorr Mountain : Climbing, Hiking & Mountaineering : SummitPost." Climbing, Hiking, Mountaineering : SummitPost. N.p., n.d. Web. 1 Sept. 2013. <http://www.summitpost.org/dorr-mountain/416282>.



Wednesday, August 14, 2013

A Piece of Ira: Unwrapping Turbidites

The first mistake many potential geology nerds make is to assume that any given rock doesn't have an interesting story.  If they didn't make that mistake I would be sitting here reading their blogs rather than writing my own.  What makes this error so common is that many of these stories are hidden, or written in languages that we can't read.  My friend Jenn brought me a wonderful story from Ira Mountain in a flat sparkly package.

Aww...Schist.  The sparkly covering on this rock is
ancient ocean bottom heated in a continent colliding oven.
Nothing wraps a rock in sparkles cheaper than mica.  Gold and Silver requires hot magma to transport heavy metals from deep within the Earth, where denser metals tend to reside.  Mica is a working man's sparkle.  It's the mud under your fingernails, or more likely the mud at the bottom of the ocean.  Fine-grained particles, like crushed up mica, drift through water under the power of the slightest current. They settle only when wave power is nearly nil.  In other words the deep dark ocean.  This mud is composed of a few things, but mica contributes heavily to the mix.  Of course, you'd never know it because the particles are so small.  Finishing the shiny package means burying the rock and crushing it between a continent, say North America, and a microcontinent, perhaps a prehistoric piece of land that now makes up shoreline on Maine, Greenland, the United Kingdom and Scandinavia called Avalonia. The heat and pressure caused small particles to migrate toward one another creating the large sparkles we now see.

Quartzite Revealed.  Notice the blockier texture on the
bottom half of the rock.  There is a thin layer of schist
below the quartzite,
Of course, you can't just wrap wrapping paper.  A glance between the layers of gray-green mica reveals a reddish blocky layer with a sugary appearance that has been compared to the texture of a gumdrop. This is where the surprise and the story lie.  Quartzite, unironically, is made out of quartz. Because quartz won't break down into to tiny pieces the way mica does, its grain size tends to bottom out at a 0.0025 inch.  The mass provided by this bulk causes even fast moving water like that on a wavy coastline to drop sand grains like they were hot, much to the enjoyment of southern Maine's beach-goers.  Crush that sand in the vise of continents and you get quartzite.

So what brings the unmoving abyss of the ocean bottom next to the active coast.  One possibility is time.  Sea level has fluctuated throughout geologic time.  To whit, the Hannaford in West Falmouth was built on ocean bottom from the ice age, and taking I-95 north of Gray reveals sandy roadsides that may be beaches of the same time period.  This sort of shift in water level is certainly capable of creating a rock that transitions from mudstone to sandstone and back again, or post crushing, a quartzite sandwich, with schist bread.

But there is another possibility.  The Carrabassett Formation, out of which the north half of Ira Mountain has been cut, is known for its turbidites.  Imagine an underwater ridge.  The top of the ridge, exposed to the movement of waves and the final surges of upland streams, plays host to hefty sediments like the aforementioned sand.  The bottom of the ridge, protected from the rigamarole, cradles the tiny clays. Then something happens.  A stream changes course.  A rogue wave mixes things up.  The ridgetop sediments, perhaps already precariously perched, fall down.  The movement stirs up everything, creating a stew of water, sand and clay.  As time passes the turbid water clears again, first dropping the heavy sand, then setting down the lighter clay.  This process would repeat again and again over the life of the ocean and the ridge until these layered sediments became stone.

Which of these possible histories is true is unclear.  Maybe this detail of the story is unwritten, or maybe I just haven't learned how to read this piece of the language.  It is the hope that we might know more, that there is some unwrapped gift, that keeps me looking and keeps me learning.

Adams, Dennis. "About Beach Sand."Beaufort County Library. Beaufort County Library, Web. 14 Aug. 2013. <http://www.beaufortcountylibrary.org/htdocs-sirsi/beachsan.htm>.

Dorais, Michael J., Robert P. Wintsch, Wendy R. Nelson, and Michael Tubrett. "Insights Into The Acadian Orogeny, New England Appalachians: A Provenance Study Of The Carrabassett And Kittery Formations, Maine." Atlantic Geology 45 (2009): 50-71.

Hanson, Lindley . "The many expressions of a New England formation." Vignettes: Key Concepts in Geomorphology. SERC, Web. 15 Aug. 2013. <http://serc.carleton.edu/vignettes/collection/25133.html>.

Schieber, Jürgen . "Sedimentary Structures." Indiana University. Indiana University, n.d. Web. 15 Aug. 2013. <http://www.indiana.edu/~geol105/images/gaia_chapter_5/sedimentary_structures.htm>.

Weller, Roger . "Schist Photos." Virtual Geology Museum. Cochise College , 24 May 2013. Web. 15 Aug. 2013. <http://skywalker.cochise.edu/wellerr/roc




Saturday, August 3, 2013

The Long View: The Bones of Casco Bay

In his book, Roadside Geology of Maine, D.W Caldwell compares the islands of Casco Bay to the bones of a hand.  The view from the dock on Mackworth Island provides a view of these bones.  Like paleontologists we can use these bones to tell the stories of the past.

The view from Mackworth Island pier.  The rock that comprises farther islands
formed further in the past, because the land bows upwards.  The space between
islands tells us there was weaker rock there that has since eroded.
The bones were not always the long linear ridges you see before you.  In fact 470 million years ago you would have been looking at a flat landscape lain down by volcanos and the deposition of sediment.  A collision 400 million years ago changed all of that.  If you stood on the coast in Falmouth Foreside you'd be standing on the crest of a wave created by the collision.  The rocks between this apex and the outward islands were folded into a sine curve (a syncline to a geologist) as the microcontinent Avalonia tried to cuddle up closer to prehistoric North America.  The view from the pier provides a look over the trough of this wave and up to the next crest.

A representation of a syncline.  As you look across the bay imagine
standing on the flat edge of the gray near the anticline.  You
look forward past younger rock (brown) toward older (light tan)
While the wave still persists, it is not all it once was.  400 million years of water, ice and wind have shaved off a few pounds.  As you might expect the crests have lost the most weight.  This means the younger rocks on the peaks have been removed, allowing us a look at the older rocks below.  For this reason the farthest islands are the oldest rocks.  Effectively, as you look across Casco Bay, you look back in time.  So, what do you see?

It might be helpful to think of there being two rows of islands - The Great Diamond row and the Peaks Island row.  The back end of each of these islands is made of volcanic rock.  Volcanos form from melted rock and nature makes that happen by plunging older rock beneath Earth's surface.  This tends to happen when a continent (Avalonia) pushes its way across the Earth, submerging ocean bottom as it goes.  The two Atlanticward sides of these islands represent periods of time when Avalonia was encroaching on North America, but one didn't follow the other immediately.

These time periods when Avalonia was hauling across the world were punctuated by peaceful times of rest and erosion.  The front half of the Peaks Island Row, which includes Long Island is made up of the sediments that formed as the first film of volcanic rock broke down.  These sediments would have continued to pile up until volcanos started pumping out lava again.  When Avalonia resumed its movement, the volcanoes recommenced spewing, and the back half of Great Diamond and all of Little Diamond came into being.  When the conveyor belt stopped again, erosion and deposition started anew.  Some layers were tougher, some were weaker.  The strongest became Cow and Chebeauge
Islands and the front half of Great Diamond.  The weakest were torn apart by glaciers or washed away by streams.  Portland Harbor, which divides Portland and South Portland formed as the Fore River provided just this sort of differential erosion clearing schist and limestone from between banks of harder volcanic rock.

The bones of Casco Bay are what's left after 400 million years of erosion have cleaned off the flesh of weaker rock.  These remains tell the story of Avalonia's delivery to the shore of North America, and it can all be seen from Mackworth Island.

Caldwell, Dabney W. Roadside Geology of Maine. Missoula, MT: Mountain Pub., 1998. Print.

Hussey, Arthur M., and Henry N. Berry, IV. "Bedrock Geology of the Bath 1:100,000 Map Sheet, Coastal Maine." Maine Geological Survey: Bedrock Geology Bath 100K Report. Maine Geological Survey, 1 Feb. 2008. Web. 03 Aug. 2013. <http://www.maine.gov/doc/nrimc/mgs/explore/bedrock/b42/casco.htm>.

Marvinney, Robert G. "Simplified Bedrock Geologic Map of Maine." Map. Augusta, ME: Maine Geological Survey, 2002.

Osberg, Philip H., Hussey, Arthur M., II, and Boone, Gary M. (editors), 1985, Bedrock geologic map of Maine; Maine Geological Survey (Department of Conservation), scale 1:500,000

"Maine Geologic Map Data." Maine Geologic Map Data. 05 Apr. 2013. Web. 03 August 2013.

Friday, July 26, 2013

New England's 50 Finest

Maine's 21 Finest.  Mountains with the tallest stature
independent of taller mountains
Recently a fellow blogger posted a list of New England's 50 Finest Peaks, or peaks with the tallest stature independent of another peak in the New England region. Maine is host to 21 of these. The map got me thinking. The peaks follow mostly straight line parallel to the slant of many of Maine's rock formations - the primordial continent that makes up the Chain of Lake region, the host of (once) tropical islands that collided 450 million years ago and the Japan-sized micro-continent that asserted itself onto the continent (and later split up) 350 million years ago.  So what is the source of our 21 finest?  The answer seemed to be none of the above.

The Grenville province makes an appearance in Maine
though not sufficient to host our tallest mountains.
The Blue Ridge Mountains in the southern United States and the Adirondacks in New York are formed from the remains of the Grenville mountain building event that plastered the Chain of Lakes onto North America around a billion years ago.  These monumental ranges may add credence to the idea that this billion year old collision led to our region's greatest mountains, but the evidence falls short.  First, although a few of the high peaks (Caribou, Kibby and Snow) reside in the area, the Grenville Province makes only a brief appearance in the left most corner of Maine.  The gneisses here, though mountainworthy, cannot claim the majority of the 21.
A fleet of ancient islands remain hidden in northern
Maine.  The 50 finest do not grace their shores.
Mount Greylock in Massachusetts, one of the 50 Finest, is a hunk of ocean bottom that got shoved up over the early North American continent in an event called the Taconic mountain building.  During this event an arc of small islands rode the tectonic plates onto the coast of pre-America.  Looking at a geological map of Maine reveals a clear series of these islands across northern Maine, not far from our largest mountains.  But none of these peaks grace the shores of these former islands - the heights are highest in the spaces in between.  So, the question remains, where did we get our giants?
A smaller continent, called Avalonia collided with
a proto-North America 350 million years ago, but could the
collision create a chain of islands 50 miles inland?
The Camden Hills are part of Avalonia, a microcontinent that slid into position on the coast of Maine 350 million years ago.  The ruffled sediments of this invading island continent make up Mount Megunitcook, Mount Battie and the rest. Could this collision also have created Maine's greatest peaks? The answer, finally, is yes and no.  The colliding of continents is no small thing, no matter how micro they may be.  The smashing was enough to give rise to the coastal mountains, but not sufficient to create the peaks almost 50 miles from the point of impact, so what was?

Almost all of Maine's largest mountains are underlain by
igneous rocks that welled up to the surface when Avalonia
collided with Maine.  A similar series of rocks got shoved
under Avalonia earlier in time creating smaller giants,
like Cadillac Mountain in Acadia.
The slab of Avalonia that got shoved underneath Maine traveled the 50 mile distance as it melted with depth.  Without crumpling, some of this molten rock floated up to Earth's surface forming volcanoes and much of the rest remained as underground stores of magma that cooled in place.  During its formation, this mountain range wouldn't have looked too different from the modern Andes, but 350 million years takes its toll.  Much of the volcanic rock has been eroded away (though some remains, notably as the Travelers in Baxter), so what has persisted is the roots of those mountains, particularly granite.

"Blue Ridge Province." The Geology of Virginia. William and Mary Department of Geology. Web. 26 July 2013 <http://web.wm.edu/geology/virginia/provinces/Blueridge/blue_ridge.html>. Website

"Camden Hills State Park." Camden Maine Sightseeing Attractions. Take Me 2 Camden Maine. Web. 26 July 2013. <http://www.camdenmainevacation.com/camden-hills-state-park.php>.
Website

"Maine Geologic Map Data." Maine Geologic Map Data. 05 Apr. 2013. Web. 03 July 2013.

"Taconic and Acadian Orogenies." Jamestown, Rhode Island. Web. 26 July 2013. <http://www.jamestown-ri.info/acadian.htm>.

Sunday, July 21, 2013

Tuesday, July 16, 2013

A Trip to Baxter Four Hundred Million Years Ago

To visit Baxter State Park during Devonian time would have been quite an experience.  Devonian time extends from 419 million years ago, when fish were just starting to widen their grip as rulers of the ocean, to 359 million years ago, when amphibians were testing their new toes on continental soil.  It is during this period of prehistory when almost the entirety of Baxter's bedrock was lain down.

419 million years ago, to travel the path that one takes to the north entrance of the park from Patten would require a boat.  Paddling north on the route that 159 takes, you'd hit land not far south of Shin Pond and a long portage would take you over the island arc and continue you on your way.  The island extends into the realm of the park only in so much as the rains tearing apart the island, at a snails pace, were delivering the islands sedimentary fragments into the surrounding ocean.  The heavier sand dropped first in a wide delta, while the smaller silt and clay drifted farther into the ocean, only to be dropped when the stream's energy had been almost fully spent.  The sandstone that was once the delta can be found along the eastern edge of the park, while the old ocean bottom wraps the northern and western sides.

The trip up Katahdin would have, in fact, been a descent.  While the portage island was being torn apart, southern Maine was plunging beneath northern. As the ocean bottom sank, it melted.  As it melted it rose, creating an upside down tear drop of magma not far from the surface, but still a ways down from Baxter Peak's current stature.  As the magma cooled, minerals formed creating the small, but visible crystals of the Katahdin granite.  The magmatic elements paired off, leaving behind the ingredients of water vapor.  The bubbling gas rose to the top of the magma chamber.  As the magma hardened around the bubbles it left cavities in which different minerals could form.  The change from the liquid magma chamber which formed the base of Katahdin to the frothy top, which formed the peaks is visible today as the white, even grained granite evolves into reddish, multi-textured granite.

While the Travelers are smaller in stature now, they literally rose out of Katahdin during the Devonian.  The Traveler Rhyolite was the volcano to Katahdin's magma chamber.  A trip there means braving molten lava, but also burning ash.  A hellish expedition to be sure, but at least there wouldn't be any black flies.  The drifting ash interbedded with the lava and then flowed down slope.  In modern times the flow is visible because the gray ash is flattened amidst the white rhyolite.

Later in the Devonian, a trip down the South Branch Pond Brook, geologically, wouldn't have been too much different than it is now.  The towering volcanoes, like the mountains that now stand, would have provided a prime environment for raging rivers powerful enough to break apart and then round the edges of chunks of rhyolite.  Smaller particles would be taken farther off to sea.   This order is preserved in the sequence of rocks below the falls - rhyolite, conglomerate, finer-grained sedimentary rock.

With current technology as a limit, an adventure in Devonian Baxter State Park is of course an impossibility.  The current landscape becomes our only time machine through which to view this exciting period in Maine's history.

Osberg, Philip H., Hussey, Arthur M., II, and Boone, Gary M. (editors), 1985, Bedrock geologic map of Maine; Maine Geological Survey (Department of Conservation), scale 1:500,000

Rankin, Douglas W., and Dabney W. Caldwell. A Guide to the Geology of Baxter State Park and Katahdin. Augusta, Me.: Maine Geological Survey, Dept. of Conservation, 2010. Print.

"Maine Geologic Map Data." Maine Geologic Map Data. 05 Apr. 2013. Web. 03 July 2013.


Wednesday, July 3, 2013

A Tale of Two Conglomerates: Chapter 3

This is Chapter 3 of a 3 part blog post.  Click here to read part 1 or here to read part 2.

Chapter 3: Metamorphism
When we last left our conglomerate heroes Mount Battie was hanging out around the South Pole, and Mars Hill near the equator.  As you can probably guess they didn't stay put.  Mars Hill and what is called the Laurentian Continent sped north, but Mount Battie and the Avalonian microcontinent sped faster.  The result: a Mack truck v. Geo Metro collision of geologic proportions (in other words, incredibly powerful, and extremely slow).  This last segment of the post is the claims adjuster's report, with metamorphism in the rocks marking the damage.

Metamorphism is a process in which rocks are changed by heat and pressure, and the Midcoast certainly endured both during the collision.  Before the collision, the sandstone that made up both the clasts, and the matrix, would have been indiscernible from sand except for the fact that the sand was cemented together into a rock.  After the collision geologists find a set of minerals called amphibolite.  Unable to form under different conditions, amphibolite tells our adjuster that the collision caused a pressure equivalent of between one and six of those Mack trucks resting on every inch of rock, while the temperature rose to around 1000 degrees fahrenheit.  Under these conditions a literal Geo Metro would be obliterated.  Our figurative car is merely transformed.  The heat and pressure of the continents colliding is enough to recrystallize the sand - converting them from discernible grains into an interlocking mass, which is called quartzite.

This is not to say that the Laurentian truck did not take damage.  Androscoggin County endured an equivalent amount of metamorphism.  But if the Midcoast and Androscoggin County were the respective front bumpers of our Metro and our Mack Truck then Mars Hill is the back end of the truck, experiencing little damage.  The clay particles in the shale clasts, under similar conditions to Mount Battie, would have recrystallized.  This would have made the pebbles look like miniature disco balls, called schist, within their matrix.  Limestone can endure a lot of heat. The limestone matrix may have remained limestone, however, it is also possible that other materials like quartz may have been injected through the rock.  In this scenario quartz, or silica, replace some of the elements in a calcium carbonate limestone creating what is called a calc-silicate rock. Instead, what we are left with looks like what we started with a mixture of limestone mud and pieces of rock all piled together heated scarcely above the temperature necessary to turn the amalgamation into stone.

Bartok, Peter. "Geology of Ireland and the United Kingdom." Ireland and United Kingdom. Tarryton, NY: Marshall Cavendish, 2010. 15-16.

Mottana, Annibale, Rodolfo Crespi, and Giuseppe Liborio. Simon and Schuster's Guide to Rocks and Minerals. Ed. Martin Prinz, George E. Harlow, and Joseph Peters. New York: Simon and Schuster, 1978. Print.

"How Much Does a Mack Truck Weigh?" Ask.com. Web. 03 July 2013.

"Maine Geologic Map Data." Maine Geologic Map Data. 05 Apr. 2013. Web. 03 July 2013.

Monday, July 1, 2013

A Tale of Two Conglomerates: Chapter 2

This is Chapter 2 of a 3 part blog post.  Click here to read part 1.

Chapter 2: The Matrix
Conglomerates share there stories in several ways.  The pebbles that fall together to make the rock tell a story of what came before.  The stuff that holds the rock together - the matrix - speaks about what was happening when the rock came together.

Four hundred and fifty million years ago, Mars Hill would have been pretty close to the Equator.  This time period also happened to be when coral were distributed widely around the world.  These facts were unknown to me at the time I first visited Mars Hill.  What I did know, however, was that Mars Hill was not far from a town called Limestone.  I looked at those clasts, and I looked at the stuff that held them together (called the matrix in the geology world), and I wondered.  I have since broken my piece of conglomerate and, logically, dropped it in vinegar.  The neat thing about limestone is that you don't have to wonder for long.  Dropping limestone in vinegar causes a reaction between the acetic acid of vinegar and the limestone base, causing carbon dioxide to fizz off.  Soon after the rock hit the bottom of the mug, bubbles started rising to the surface of the vinegar.  Four hundred and fifty million years ago, about the same time that ocean bottom rock was being torn apart, a coral reef, not far from Mars Hill was breaking down as well.  While the majority of this calcium carbonate piled up on flat ocean bottom, creating the substrate for Aroostook County's potatoes, some followed the flow of water over some sort of cliff into some kind of deep water canyon allowing shale pebbles and limestone mud to mix together.

The pebbles that make up the Mount Battie conglomerate are held together by something else.  500 million years ago, Mount Battie was in a part of the world not very likely to host coral.  The Avalonian microcontinent, perhaps similar in form to today's Japan, was on the bottom part of the world, below the 60th parallel.  The matrix here, insoluble in acid, is quartzite, indicating a sandy environment.  Layering at the site indicates the sand gathered in an ocean basin, where wave action swept away most of the smaller sediments, leaving behind sandstone pebbles in a matrix of sand.  This shore line would have been a bit cold for developing coral reefs, excluding the development of limestone in the area.  This gravelly beach the stage for our future coastal mountain.      
Modern World Coral Reef Locations - Credit: NASA

Berry, Henry N., IV. "The Bedrock Geology of Mount Battie, Camden." Maine Geological Survey: , Maine. Maine Geological Survey, 19 Apr. 2012. Web. 01 July 2013. <http://www.maine.gov/doc/nrimc/mgs/explore/bedrock/sites/jul01.htm>.

Scotese, C. R. "Earth History." Plate Tectonic Maps and Continental Drift Animations. PALEOMAP Project. Web. 01 July 2013. <http://www.scotese.com/earth.htm>.

Wang, Chunzeng, Gary Boone, and Bill Forbes. "Geology of Mars Hill Mountain and Vicinity." Http://goaroostookoutdoors.com/. Web. 1 July 2013. <http://goaroostookoutdoors.com/sites/default/files/trails/maps/mars_hill_geology2.pdf>.

Friday, June 28, 2013

A Tale of Two Conglomerates: Chapter 1

A name should tell you something.  When it comes to rocks this is generally the case.  In sedimentary rocks, the name tends to give away the energy of the sedimentary environment.  Sandstone forms wherever sand might gather - like a beach with strong waves or a fast moving stream.  Shale evolves where clay might gather, say the bottom of the ocean.  Conglomerate, along similar lines, is birthed where gravel collects - perhaps a raging river or a bar in a particularly active part of the ocean.  The name conglomerate tells you that there was enough energy to carry rocks there, but the rock tells you a lot more.

Last summer I visited two conglomerate outcrops; one was Mount Battie in Camden, the other Mars Hill Mountain in Mars Hill.  These two rocks couldn't be any different while sharing the same name.  Each rock tells this history of its own place in three distinct chapters.

Chapter 1: Clasts
Mount Battie Conglomerate - Round Quartzite Clasts Circled
One neat thing about conglomerates is there are two sets of rocks with stories to tell: the conglomerate itself, and the rocks parts that are cemented together within it.  The rock parts (or in geology speak, clasts) at the two sites are surely at odds.  The Mount Battie conglomerate is made up of rounded, light colored clasts about the size and appearance of a pale gray gumdrop.  The gumdrops are quartzite.  If we could turn back the clock we would see that these chunks (like all quartzite) were once sandstone.  Imagine a wave rocked ocean off the coast of some forgotten continent.  Sand piles up (pure sand; we know this because the quartzite is so light in color) and eventually, chemical intrusion turns it from packed sand to sandstone.  Once loose sand, now solid rock, as they say, even this shall pass.  Perhaps the land gets raised and rivers cut through.  The slab of rock, once a beach, is broken by time and water into smaller pieces.  As the water courses the rocks get rounder and rounder.


Mars Hill Conglomerate - Flat Black Clasts Squared, Jagged
Edge Visible on Top Piece
Mars Hill has a different story.  The rocks that comprise this conglomerate are flat and black.  The flatness (and perhaps the darkness) suggests that this rock may be a shale formed in a  low energy environment.  This rock probably sat at the bottom of some ocean.  Layer upon layer of fine-grained sediment coasted to the seafloor at a ridiculously slow pace, with added phytoplankton and low oxygen levels coloring the sediment black.  Here too the land becomes elevated.  Streams shatter the shale and push it downstream.  The current softens the edges a bit before the slivers of rock reach an endpoint.

The endpoint, however is just an endpoint, not the end.  The beach, the ocean bottom, they are just the first step in the stories told by these rocks.  Check back soon for chapter 2 and 3.

Dietrich, Richard Vincent, and Brian J. Skinner. Rocks and Rock Minerals. New York: Wiley, 1979. Print.

Way, Bryan. "Black Shales." 1 Dec. 2006. Web. 28 June 2013. <http://faculty.umf.maine.edu/eastler/public.www/Black%20Shales.pdf>.







Monday, June 24, 2013

The Geology Hikes Map

The predecessor to the Maine Geology Hikes Blog, was the Geology Hikes in Maine Map.  At this point there are 14 locations with brief geology stories for each icon.  Recently, I've linked blog entries relevant to a few places in their icons.  Feel free to peruse the map as it is now, but I'd also like to add new sites to the map as well.

Specifically, I'd like to update it with places you plan to visit.  Over the next week list places you are thinking of hiking here in the comments or on the Maine Geology Hikes Facebook page and I will write a brief description of the geology of the location to which you will be going.  Disclaimer: I probably won't be able to ground truth many locations before next weekend, so the descriptions will be based on research at a distance.  I'll respond to your suggestions in the comments and include new red icons on the Geology Hikes in Maine Map.  The locations will remain in red until I can ground truth them.

Some notes 1) Your location needs to be in Maine,  2)You'll be able to see more of the geologic history if it is a rocky location, 3) Include some detail about the location so I can find it on maps.  Consider including the town it is in, the road you will be entering from, or a link to a trail description.


View Geology Hikes in Maine in a larger map

Friday, June 21, 2013

Maine's Earthquakes

Today there was a small earthquake about 7 miles from Augusta Maine.  The quake was a 2.6 on the Richter Scale.  Because the Richter scale is logarithmic, each point it rises means the quake is 10 times stronger.  By extension, this quake was about 100 times gentler than the 4.5 that many of us in southern Maine felt last October 16th.

We're used to hearing about big earthquakes: The 2010 Haiti earthquake (7.0), the 2011 Japan earthquake (9.5, 10,000,000 times as powerful as the one felt today) or the ones that occur along the San Andreas in California.  All of these occur on active plate boundaries where one plate is shoving under or, in the case of California, past another, but what's happening in Maine?  There haven't been any active plate boundaries in Maine for more than 200 million years.

If you could look at Maine's Carfax report it would not look good.  Maine is the victim, nay product, of several collisions with other landmasses.  Each one left Maine with several small faults, where the old continents docked.  Then there was the stretching.  When Pangaea split the continent spread to fill up the old space.  Some parts of once solid rock sank down, while others remained aloft.  The result: despite it's beautiful exterior, our state has some pretty severe internal damage.

There are faults on the surface within 15 miles of today's earthquake, but the earthquake occurred 3.1 miles underground.  It's difficult to assign blame for the earth shift that occurred, but we can be assured that it is a result of Maine's storied tectonic history.

"Central Maine Feels 2.6 Magnitude Earthquake." Bangor Daily News. 21 June 2013. Web. 21 June 2013. <http://bangordailynews.com/2013/06/21/news/state/central-maine-feels-2-6-magnitude-earthquake-sidney/>.

"M2.6 - 2km W of Sidney, Maine." Earthquake Hazards Program. United States Geological Survey, 21 June 2013. Web. 21 June 2013. <http://earthquake.usgs.gov/earthquakes/eventpage/usc000hx15#summary>.

"Maine Earthquakes 1997 to Present." Maine Geological Survey. State of Maine. Web. 21 June 2013. <http://www.maine.gov/doc/nrimc/mgs/explore/hazards/quake/quake-recent.htm>.

Wednesday, June 19, 2013

The Long View: Watching the Earth Move

It surprised me when I read that you could see Mount Washington from a hilltop in Falmouth, so when I climbed Stone Ridge, I was impressed with the amazing view.  My first visit on a clear day in April gave me a Kodachrome view of the mountain and the broad landscape between here and there.  It wasn't until much later that I realized that this might just be the perfect perch from which to watch the earth move.

Of course the White Mountains were just the starting point (well, really Mount Royal in Montreal, Canada, but you can't see that far).  One hundred eighty million years ago there was a hot spot under what would one day become eastern New Hampshire.  In geology, a hot spot is a thin stream of Earth's heated innards bubbling up towards the surface over a long period of time.  When the hot spot underlies a continent the result is violent, explosive eruptions at the surface.  These eruptions and the super-heated magma below the surface built the White Mountains over twelve million years.

The hot spot never moved, and it never stopped bubbling.  The good news for the residents of North Conway, is that New Hampshire did.  When Pangaea split apart, opening the Atlantic Ocean, North America pushed westward, and Africa pushed (relatively) eastward.  By one hundred twelve million years the continent had moved to the point that the hot spot underlay Denmark, Maine, building Pleasant Mountain.  By one hundred eight million the Earth was bubbling in Brownfield, forming Burnt Meadow Mountain.  

The View from Stone Ridge in Falmouth.  Burnt Meadow Mountain is in the center, the White Mountains on the right, and Pleasant Mountain in between.  All are highlighted in red. (a lot of time on Google Earth may not have made up for poor spatial ability; leave comments if you think I've misidentified the mountains).
Soon after the North American continent escaped the fiery clutches of the hot spot, but the hot spot didn't quit.  Between 100 and 75 million years ago it left a trail of underwater mountains (called seamounts) stretching from the continental shelf to the mid-ocean ridge.  At that point, the seamounts seem to sputter out, that is until they emerged on the opposite side of the ridge, where as recently as 10 million years ago they appeared to be approaching Africa and the Canary Islands (or really Africa was approaching the hot spot).

Of course we can't see all of that from Falmouth, but we can see a few million years of continental progress, before the horizon shades our view.  On a clear day, the White Mountains are visible and Pleasant and Burnt Meadow Mountain can be seen as well.  The picture provides not just beautiful scenery, but a window into the tectonic motion that occurs over millions of years.

"Science Reference: Hotspot (geology)." ScienceDaily. ScienceDaily. Web. 19 June 2013. <http://www.sciencedaily.com/articles/h/hotspot_(geology).htm>.

Girty, G. H. "Chapter 2: Volcanoes." Perilous Earth: Understanding Processes Behind Natural Disasters. Department of Geological Sciences, San Diego State University, June 2009. Web. 1 June 2013.<http://www.geology.sdsu.edu/visualgeology/naturaldisasters/Chapters/Chapter2Volcanoes.pdf>.

Watling, Les. "Geological Origin of the New England Seamount Chain." NOAA Ocean Explorer Podcast RSS. Web. 19 June 2013 <http://oceanexplorer.noaa.gov/explorations/03mountains/background/geology/geology.html>.

Zartman, R. E. "Geochronology of Some Alkalic Rock Provinces in Eastern and Central United States." Annual Review of Earth and Planetary Sciences 5.1 (1977): 257-86.

Friday, June 14, 2013

Resources: Identifying Rocks

The rock identification guide I have is an excellent resource.  It has beautiful pictures, detailed descriptions and it is well organized, but it is easy to be overwhelmed by minutia and jargon. With words and phrases like hexagonal dipyramidal, sphalerite  and chlorite-amphibole-epidote-albite schist, one can feel tempted to not event try to learn.

There are a few great online resources to assist beginners in the identification of rocks.  If you want to try, check out these to sources:

The Rock Key at rockhounds.com - This site has an clear dichotomous key, which helps you select the correct rock by making a series of either/ or choices.  Some of the steps require advanced equipment like a nail or piece of glass, but you can figure most of it out by just looking at the rock and clicking through.  There is good introductory material at the top of the page, and good synopses of the rock types down below.

Rock Galleries at geology.about.com - Sometimes it can be easier to get visual affirmation of the rock type and for that purpose these galleries are a great start.  Once you have determined the type of rock (igneous, sedimentary or metamorphic) these galleries have clear pictures of rocks in one location.

Of course these are just a couple resources.  If you know of others or have questions about how to use these please leave comments.

Tuesday, June 11, 2013

A Piece of Bradbury: Rebel Pegmatite

Some things in this world are predictable.  There is a very clear relationship between how big the crystals in an igneous rock are, and how long it took to form.  But some rocks rebel.

The rule of igneous rocks is simple. If crystals are small - as in a piece of basalt or rhyolite - the rock froze fairly quickly, having risen to the Earth's surface before dropping in temperature rapidly.  If the crystals are large, as is the case of this piece of granite I found at Bradbury Mountain, it means the rock formed deep underground, where the heat of the Earth allowed each crystal to gestate to full visible size before turning fully solid.
The rock that makes up Bradbury Mountain formed as Africa shoved its way underneath the North American plate - squeezing magma into Maine's underbelly.  Of course at that point the rock was covered with a thick blanket of rock thrown up by earlier parts of the collision.  The magma cooled slowly, and the crystals grew to the size you now see, following the rule to a tee.

Turn the rock around however, and you find these rebels, younger crystals, forming faster and larger than their granite brothers and sisters.  These crystals are pegmatite, effectively a large crystalled rock with the same make up as the granite on the reverse.  Pegmatite drew people to the site in the 1920s because the large crystals of the mineral feldspar were easily gathered for making ceramics.  But how did it get there?

As it solidified, the mass of magma that had squeezed under Maine, shriveled like a raisin.  The contraction created a gap with the surrounding rock, as well as spiderweb of cracks near the edge of the hardening granite.  These became a network of passageways through which left over magma could flow.  The remaining magma had all of the components of the original, but with a higher concentration of materials that couldn't form minerals, among others water.  This extra stuff became a super serum for crystal growth, filling in the empty space with megacrystals, a hundred times the size of their brethren.


Landes, Kenneth K. "The Paragenesis of the Granite Pegmatites of Central Maine."American Mineralogist 10 (1925): 355-411.

London, David. "Granitic Pegmatites: An Assessment of Current Concepts and Directions for the Future." Lithos 80 (2005): 281-303.

Simmons, Skip. "Pegmatite Genesis: Recent Advances and Areasfor Future Research." Proc. of Granitic Pegmatites: The State of the Art – International Symposium, Porto, Portugal. Web. 11 June 2013. <http://www.fc.up.pt/peg2007/files/simmons.pdf>.

Zieg, M. J., and B. D. Marsh. "Crystal Size Distributions and Scaling Laws in the Quantification of Igneous Textures." Journal of Petrology 43.1 (2002): 85-101.

"Bradbury Mountain State Park." Maine Bureau of Parks & Lands. 2009. Web. 10 June 2013. <http://www.maine.gov/cgi-bin/online/doc/parksearch/search_name.pl?state_park=12>.


Sunday, June 2, 2013

Mount Agamenticus: Maine's Kilimanjaro

Mount Kilimanjaro, Earth's highest free-standing peak, projects nearly 20,000 feet into the African sky, towering above the plains and valleys below.  Mount Agamenticus projects as well, but to a decidedly lesser 700 feet. Despite the clear difference in stature, the two mountains have a lot in common.

Mount Kilimanjaro Dec 2009
Mount Kilimanjaro in the Distance
The East African Rift Valley is slowly growing wider, tearing the African continent apart at the Earth's seam.  At its center the warm interior of the Earth rises to the surface, creating a wending line of volcanoes that stretches from the Red Sea in the North to Lake Malawi in the south. The upwelling magma creates pressure that pushes the parts of the continents away from the spreading center.

It is a Mole Hill:  Mount Agamenticus from Kennebunkport Shore
Mount Agamenticus in the Distance
As a rule, the eruptions of magma stick to that central path, but the volcanoes are a little more unruly than the general might suggest. Along the rift, magma has three options. First, it can ooze out of vents, forming thin dikes. Second pure rift magma can create broad, gently sloped mountains called shield volcanoes.  Finally, rift magma can melt and mix with other rock to spawn energetic explosive eruptions that pile up magma and ash into tall steep sided sentries that sit beside the rift called stratovolcanoes.  Kilimanjaro obviously fits into this third category along with Mount Kenya (in Kenya) and Mount Meru (in Tanzania).

Actually, so does Mount Agamenticus, right here in Maine.  Or at least it did. Mount Kilimanjaro started to form about 2.5 million years ago, and its last eruption occurred about 175,000 years ago. While this may be a long time on a human scale, on a geologic scale Kilimanjaro is a young Turk.  Imagine Agamenticus on a similar boundary two hundred million years ago: the Maine coast is bidding a fond adieu to the North African shoreline after a short tryst as Pangea and Agamenticus rises 20,000 feet above the western coast. The volcanic center of this rift valley is widening and filling with the water that will someday become the Atlantic Ocean.  As it does, streams and ice begin the shortening process of our once giant sentinel.  Fast forward a hundred million years - the mountain is smaller, the ocean wider and about halfway to the form we now see.  One hundred million more and the mountain is little more than 1/30th its former height, the spreading center nearly 1500 miles away.  

Bloom, Arthur L. Geomorphology: A Systematic Analysis of Late Cenozoic Landforms. Upper Saddle River, NJ: Prentice Hall, 1998. Print.

Brooks, John A., Gust, David A., and Hussey, Arthur M., II, 1989, The geology and geochemistry of the Agamenticus Complex, York, Maine; in Berry, Archie W. (editor), Guidebook for field trips in southern and west-central Maine: New England Intercollegiate Geological Conference, 81st Annual Meeting, October 13-15, 1989, University of Maine at Farmington, Maine, p. 1-24

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