faulker015

Watching a film set in Cape Town, South Africa, today, I wondered about the geology of Table Mountain, which looms above the city.  As is often the case, the natural history of that famous massif is complex. About 500 million years ago, during the Cambrian Period, a rift valley developed in the southern portion of a continental plate that included today's Continents of South America, Antarctica and Africa.  Initially flooded by a shallow sea, the rift accumulated sediments over the next 100 million years.  Throughout the late Paleozoic and early Mesozoic Eras, this region was folded, lifted and eroded by tectonic forces as Earth's Continents merged into Pangea and then rifted apart. Among the sedimentary rocks that formed within the ancient rift valley was a thick layer of hard quartzite sandstone; resistant to erosion, this Table Mountain Sandstone now outcrops as the steep cliffs of Table Mountain and the Cape Fold Ranges of western South Africa.  Of note, the west...

Yesterday, following two earthquakes (the second a magnitude 7.5 quake) and a series of aftershocks off the west coast of Sulawesi Island, a tsunami struck Palu, at the end of a long, narrow bay.  Both the Island and the adjacent Makasser Strait lie squarely on a southern extension of the Eurasian Plate, which encompasses all of Indonesia. Destructive tsunami's are generally triggered by Subduction Earthquakes , where one tectonic plate dips beneath another; such a subduction zone stretches along the outer border of Indonesia, where the Australian and Philippine Plates are subducting beneath the Eurasian Plate.  Yesterday's series of quakes and aftershocks are thought to have developed along a transverse fault, where two microplates (of the Eurasian Plate) are scraping past one another; such faults do not generally produce vertical lift of the overlying sea, the tectonic process that usually generates tsunamis. Geologists suspect that some vertical movement of one of the micr...

The Florida Panhandle is known for its sparkling white beaches, a trait that results from their composition.  The "sugar sand" of this region is composed of fine, ovoid quartz crystals, eroded from the Blue Ridge Mountains and deposited in the Gulf of Mexico by the Apalachicola River. Spread by currents within the Gulf, the quartz crystals are a primary component of beaches all along the Florida Gulf Coast but are least "contaminated" with shell fragments along the Panhandle.  In beaches along the Florida Peninsula and Keys, variable amounts and color of shell fragments alter the appearance of the sand; in some areas, the shell fragments predominate and the beach is gray, tan or nearly black. Here on Pensacola Beach, the white sand is dazzling in the bright afternoon sun, squeaking beneath your feet and producing a sharp contrast with the clear, turquoise water of the Gulf.  As one might expect from the above discussion, shells are small, mostly white and far less a...

Yesterday morning, we left Knoxville, driving eastward through the foggy Tennessee Valley.  After crossing the Holston and French Broad Rivers (which join to form the Tennessee), we climbed into the Blue Ridge Mountains, following the course of the Pigeon River.  Leveling out west of Asheville, we crossed the divide between the Pigeon and the French Broad Rivers, encountering the largest concentration of tent caterpillars that I have ever seen. At Asheville, we angled southward on Interstate 26 and crossed the Eastern Divide just south of Hendersonville; this Divide, which snakes north to south through Eastern Canada and the Eastern U.S., separates the watersheds of rivers flowing to the Gulf of Mexico from those flowing toward the Atlantic Ocean.  South of the Divide, we soon arrived at the edge of the Blue Ridge Mountains and were treated to a spectacular view of the Southeastern Piedmont. After undulating across the Piedmont, hemmed in by a pine-broadleaf forest, we cr...

On our way to a family wedding in South Carolina, my wife and I left Columbia this morning and drove eastward across the Glaciated Plain of Missouri.  After crossing the Missouri and Mississippi Rivers in St. Louis, we angled southeastward across Illinois, eventually fording the Wabash River (a major tributary of the Ohio) before climbing across the Shawnee Hills of southern Indiana (capped with Pennsylvanian sandstone). After crossing the Ohio River at Louisville, we drove eastward through the Bluegrass Region of northern Kentucky (underlaid with Ordovician Limestone), crossing the Kentucky River near Frankfort and again south of Lexington; the Kentucky flows northward to joint the Ohio.  At Berea, we climbed onto the Appalachian Plateau (a layer cake of Carboniferous sediments) and crossed the Cumberland River (another tributary of the Ohio) in southern Kentucky.  Entering Tennessee, we climbed across the Allegheny Front, the high, western edge of the Appalachian Platea...

Yesterday, as I flew from Missouri to Colorado, our route took us across the central latitudes of Kansas.  The low morning sun angle and clear skies provided ideal conditions for observing the topography below and I got a good look at the Smoky Hills. The Smoky Hills Province of the Great Plains stretches across north-central Kansas and into south-central Nebraska.  It is characterized by low hills that have been sculpted from Cretaceous bedrock by the tributaries of the Smoky Hill, Saline, Solomon and Republican Rivers (south to north).  That bedrock, deposited within and along a Cretaceous Sea that once covered most of the Great Plains region, is comprised of three bands: Dakota Sandstone, Greenhorn Limestone and Niobrara Chalk (east to west). Those who drive across Kansas on Interstate 70, cross the southern portion of the Smoky Hills Province between Salina and Hays; there, some ridges of the Province are adorned with turbines of the massive Smoky Hills Wind Farm....

The eruption of a volcano in Guatemala and its tragic consequences have drawn attention across the globe this week.  Some will blame the event on the random violence of nature while others will see the hand of God in the destruction and suffering.  But if you must accuse someone or something, blame the Atlantic Ocean. During the Permian Period, some 250 million years ago (MYA), the Continents had merged to form Pangea.  By the Triassic, about 200 MYA, the Tethys Sea opened, separating Laurasia (the northern Continents) from Gondwanaland (the southern Continents).  Then, during the Jurassic Period (some 150 MYA), the Atlantic began to open and the American Continents were pushed westward, a process that continues today.  In concert, the oceanic Farallon Plate was forced to subduct beneath the advancing Continental Plates; today, the Juan de Fuca Plate (in the Pacific Northwest), the Cocos Plate (west of Mexico and Central America) and the Nazca Plate (west of Sou...

During our first week in Switzerland, my wife and I will be staying in Nyon, on the north shore of Lac Leman, more commonly known as Lake Geneva throughout the English-speaking world.  Created by glacial erosion during the last glaciation of the Pleistocene, this crescent shaped lake is one of the largest in western Europe, 45 miles in length and up to 8 miles wide. Near Nyon, the deeper Grand Lac portion (to the east and southeast) gives way to the Petit Lac, a shallower and narrower section that extends westward to Geneva.  This latter portion of Lac Leman was subjected to the serial deposition of terminal moraines as the glacier melted back toward the Alps as well as sedimentation from glacial streams that entered from its north and south.  The Rhone River, now rising from its residual mountain glacier in the Alps, flows through Lac Leman and then drains it through southern France before entering the Mediterranean Sea. This afternoon, we enjoyed a spectacular view of L...

While Switzerland is famous for its Alps, which cover the southern half of the country, it also harbors a second mountain range, the Juras, which stretch along its northwestern border with France.  More than 200 miles in length, the Jura Mountain Range arcs from the Rhone Valley, at Geneva, to the Rhine Valley, at Basel. The Jura Mountains have a core and outcrops of marine Jurassic limestone, deposited in the  Paratethys Sea when dinosaurs roamed the planet; these sedimentary rocks were uplifted during the Pliocene Period of the Cenozoic Era (some 5-2 million years ago) as pressure from the ongoing Alps Orogeny rippled the landscape to their north.  While Jura means forested or mountains in regional native languages, it is also the basis for the word Jurassic , a name chosen by geologists for the middle period of the Mesozoic Era.  The Jura mountains are indeed forested except for alpine grasslands on the higher summits and sheer rock cliffs on some of the mounta...