What shall I post about next? Is the subject matter worthy of discussion? What shall I say? What shall I omit? It’s the blogger’s never-ending dilemma. By the time the end of the year rolls around, at least for me, there are always a few posts that never got written and a few images that never got uploaded. And so, with this final post of the year – in what has been a tradition on my blog for five years running – here’s my end-of-the year post (although a little belated). Please visit the same for 2012 (here), 2013 (here), 2014 (here) and 2015 (here).
So, while on vacation with clear blue skies and 1,350 miles of accessible coastline, it seemed logical to head to the beach and see what the tide had brought in. To my surprise, I discovered a fossil remnant of a unique, marine bivalve colony that is responsible for the geomorphology of southwest Florida's carbonate-producing coastline and offshore islands.
|How am I going to do any geology here?|
Southeast of Marco Island along the southwest coast of Florida is the archipelago of Ten Thousand Islands. It’s a maze of oyster shoals, mangrove trees and brackish tidal channels that are a few miles wide and up to 20 miles long. The islands are actually part of an interesting stratal sequence deposited some 7,000 to 3,000 years ago.
Following the Pleistocene ice age, Holocene transgressions began to flood the Florida shelf. A basal peat layer formed below sea level that overlies eroded Pliocene and Pleistocene limestones. Quartz and shelly sands followed as the sea level rose. Overlying the sands of the inner islands are Holocene-age oyster reef beds that are overlain by modern peat and support the region’s mangroves. The right conditions of rising seas, climate and sedimentation converged over this interval to promote reef development.
The outer islands, in addition to oyster beds, have an up to 10 foot-layer of the worm-like mollusk Petalochonchus varians. The marine gastropod is of the Vermetidae family but doesn’t resemble the coiled shell of the average sea snail and is frequently interpreted as a marine annelid, tube worm, and vice versa. The "worm snails” grow cemented together in complex, anastomosing colonies locally known as “worm rocks.” From about 3,000 years ago, they formed a small barrier reef system until recently, when they began to experience an inexplicable global decline. On occasion, dislodged erratics wash ashore and await discovery by unsuspecting geo-beachcomers.
|An Alligator-infested Open Strand in Big Cypress Preserve Surrounded by Cypress and Deciduous Hardwood Trees|
Water lazily flows to the south and southwest at a barely perceptible rate since the landscape is almost virtually flat - only two inches per mile! As a result, it is subject to extraordinary extremes of wet and dry weather. Far more than just a stagnant pool with a high watertable, the “River of Grass” is a wide, slowly moving, freshwater sawgrass prairie or marsh. "Sheet-flow" is the frequently used, descriptive term.
|Southern Florida's hyrologic ecosystem includes the Everglades, Big Cypress and Ten Thousand islands|
West and southwest of the Everglades and confined by the limestone Immokalee Rise lies the state's other major wetland, the 1,200 sq mi swamp of Big Cypress. Eastern America's "last great wilderness" is named for its area rather than the size of its flood-adapted, deciduous trees. It's actually an extension of the Everglades hydrologic system. The two are integrally-related and similarly nutrient-poor, but their character, biology, ecology and geology are surprisingly quite different.
|The Swamp Lily or String Lilly (Crinum americanum) is actually an Amaryllis.|
|Big Cypress's Majestic, Swamp-loving Wading Bird, the Great Blue Heron (Ardea herodias)|
Water outflow from Big Cypress is eastward to the southernmost Everglades but also westward into the mangrove swamps and the Ten Thousand Islands coastal region on the Gulf of Mexico that serves as a buffer between the salty sea and freshwater marsh. For information on the geological evolution of the Florida Platform, please visit my post here.
|Looking NNW into Lost Valley From Red Pass Towards Leadfield and Titus Canyon|
Enter the following coordinates into an online mapping program such as Google Earth,
and it will take you there: 36°49' 44.12"N, 117°02'03.21"W.
The strata of Lost Valley spans time frames from Cambrian to Recent and represents continental clastic sedimentary rocks deposited on the miogeosyncline of western Laurentia (the rifted passive margin of the supercontinent of Rodinia), ash flow tuffs (the products of volcanic eruptions related to the middle Miocene multi-calderic southwest Nevada volcanic field) and lavas (Miocene to Pliocene in age). Multi-colored conglomerates and sandstones in the walls belong to the Eocene to Oligocene Titus Canyon Formation. Alluvial fan and lacustrine deposits, megabreccias and conglomerates were deposited within a fault-controlled basin and provide evidence for Early Oligocene extension before the formation of Death Valley. Banded grays are mostly limestones of the Cambrian Bonanza King Formation, while beyond are volcanics.
|The Upper Narrows of Titus Canyon|
Geologist, author and guide Wayne Ranney (here) takes in the solitude and shade of the wider, upper narrows of Titus Canyon. Water (and the rocks and boulders that it carries) funneled down from the watershed of Lost Valley are responsible for the erosive-genesis of this otherwise bone-dry canyon. It's a commentary on the tremendous carving capacity of stream cutting in association with tributary erosion and mass wasting. But in what time frame? Geologists estimate that a 1-inch rainfall over the region's 35 square-mile watershed can excavate a few hundred thousand cubic feet of material in merely 50,000 years to create the massive fans that radiate outward from the canyon's mouth at Death Valley, not far from this point. Of course, these are arid times, and don't take into account the wetter post-Pleistocene climate that came before.
|Counterintuitively, a drive down Titus Canyon takes you topographically downward into progressively younger rocks. It's because the strata has been inverted within a folded anticline.|
One distinctive canyon wall is a massive mosaic of erosion-polished, brecciated (angular, flat-sided) dark carbonate fragments of the Middle Cambrian to early Late Cambrian Bonanza King Formation. It was deposited offshore - as was the familiar and geo-equivalent Middle Cambrian Muav Limestone of the Grand Canyon to the east - on the passive margin of Laurentia subsequent to the fragmentation of the supercontinent of Rodinia. How did the "mosaic" form? Analyze it a minute before you answer.
|Dee and the Enigmatic Jigsaw Puzzle Wall of Titus Canyon|
The mosaic may have formed under severe stress, deep underground and concurrent with the formation of an anitformal recumbent syncline (large-dimensional folds that are younger at the core and lie on their side). The host rock, the Bonanza King, fractured along with the intrusion of the molten, now flowable calcite that was derived by pressure solution of the host rock. Proof of recumbency is that older formations lie above younger ones. What's your interpretation?
|A Collage of Building Materials and Architectural Styles in the Financial District of Boston|
Take a drive through any town of considerable size in New England situated on a river that powered its mills in the nineteenth century. Even where building stone was available, the buildings are all composed of brick for reasons of economy and speed of construction. Things changed for brick at the turn of the twentieth century when the demand for high office buildings and less susceptibility to earthquakes increased, resulting in the use of cast and wrought iron, and later, steel and concrete. As for the mills, they closed in New England when alternatives to water power were developed and textile production became more profitable in southern states where cotton was grown and winters were warmer.
|Postcard of the Brick-built Mill Town of Manchester, NH, on the Merrimack River|
|Typical Gray to Greenish New England Glaciolacustrine Clay Pit|
|First Phase of Construction|
The Washington Monument was the tallest building in the world upon its completion in 1884. The structure was completed in two phases, one private (1848-1854) and one public (1876-1884).
While ascending Little Haystack Mountain on the Franconia Ridge Trail in the western White Mountains of New Hampshire, my son and I came upon a large area of “needle ice” on the trail at about 3,000 feet of elevation early in the morning. It was late October, and the night had brought temperatures below freezing but without any precipitation. It was the first time I experienced such a variant of frozen, ribbon-like water and was fascinated how it forms.
|Franconia Notch State Park of the Western White Mountains of New Hampshire|
Located in the heart of the White Mountains National Forest, the notch - a New England geological term for a glacially-scoured mountain pass - is a product of the last advance and retreat of the Laurentide continental ice sheet. Eight miles of north-south Interstate 93 slices through it with spectacular cliffs of Cannon Mountain on the west (former site of the "Great Stone Face" of the Old Man of the Mountain) and peaks of Franconia Ridge (Mounts Lafayette, Lincoln and Little Haystack) on the east. The ridge is notorious for its unpredictably inclement and dangerous weather at any time of the year. Its also famous for classic glacial geomorphology. Louis Agassiz, the renowned Swiss naturalist, geologist and Harvard professor, confirmed in 1847 that continental-scale glaciers were responsible for the appearance of the landscape. In fact, the terrain north of the gap (seen above) contains Alpine-like "ancient moraines" that he studied.
Aerial photo courtesy of Bill Hemmel. Please visit him at here.
Appearing as thin, curved, filamentous and striated combs, the needle ice grows from moist, water-penetrable soil generally before melting in the warmth of the sun. Unlike frost or rime, which obtains moisture from the air, the water source for needle ice is contained within the soil. When the air temperature drops well below freezing, water in the soil may become “super-cooled” well below freezing. The cold water is drawn upward through the soil via capillary action and is rapidly frozen into ice crystals near the surface, while being “fed” as additional water seeps out from the soil and freezes. While “growing”, needle ice may lift small soil particles. Along with cyclical freezing and thawing, frozen water in its many forms contributes to soil creep and even the erosion of mountains.
Fungi, being saprotrophic, feed on decaying organic matter such as typically found in forests (called "tethered" and are related to mycorrhizal symbiotic associations with trees) and lawns (referred to as "free", since they are not associated with other organisms). The fairy ring is detectable by a circle of mushrooms as well as a necrotic zone of dead grass or, counterintuitively, a ring of thriving, dark green grass, as seen above. In the latter circumstance, the below-ground mycelium, which is somewhat analogous to the roots of vascular plants, absorbs nutrients via the secretion of enzymes from the tips of hyphae, the thread-like, microscopic filaments that comprise the mycelium.
The mycelium gradually moves radially from the center of the expanding ring, when nutrients (generally nitrogen and iron) become sufficiently depleted. When the center dies, the ring become obvious outside the necrotic zone. Surprisingly, some fungi produce chemicals called gibberellins that act like hormones, which favorably affect plants causing rapid luxuriant growth.
|Modified from victoriaweb.com|
Fairy rings are the subject of folklore, myth and the supernatural, especially in Western Europe. In France, they are referred to as “sorcerers’ rings” and in Germany “witches’ rings.” Some believe that anyone stepping into an empty fairy ring will die young. Those that violate the perimeter become invisible to those outside and may be unable leave the circle. The fairies force intruders to dance till exhausted, dead, or in the throes of madness. One of the largest fairy rings ever found is near the city of Belfort in northeastern France. It measures some 2,000 feet in diameter and, based on the rate of growth and expansion, is estimated to be 700 years old.