Saturday, April 05, 2014
The Permian Sea that dominated this part of Pangaea 250 million years ago left the gypsum rich deposits that have now been recycled to form the dunes at White Sands (previous post). This sea (or some smaller connected seas) also gave rise to large carbonate reefs, one of which has been subsequently uplifted and exposed by erosion as the current Guadalupe Escarpment (Guadalupe Mountains National Park).
Guadalupe Peak is the highest point in Texas (8751'). El Capitan, the distinctive prow immediately to the south, marks the southern end of the Guadalupe Escarpment. Carlsbad Caverns was carved (dissolved, actually) into the core of the reef much later, aided by the presence of hydrocarbons in the adjacent basin that leaked hydrogen sulfide and produced sulfuric acid, a much more effective cave-forming agent than the more common carbonic acid.
The Capitan Reef faced eastward across the Delaware Sea (an arm of the larger Permian Sea). The Delaware Basin and the Midland Basin farther east are now both major oil and gas fields and driving south towards Carlsbad I was reminded of this by the pump jacks and well heads, the pipe yards, and the lines of red Halliburton trucks. I spent the fall of 1981 in Schlumberger's training program in Midland and spent weekends exploring west Texas in my new little pickup truck. That was a long time ago!
I suppose there may have been beaches on the shores of this Permian ocean - but the environment behind these reefs was probably pretty quiet and the shores were probably muddy and perhaps vegetated (although I suspect they didn't look like the mangroves or salt marshes you might find in similar settings today).
Posted by Gravel Beach at Saturday, April 05, 2014
Labels: new mexico
Friday, April 04, 2014
I try to stick to a fairly standard theme in this blog. Posts are places (not issues or topics or events, and only occasionally people). They are built around photos I've taken myself (usually within days or sometimes weeks). The subject material is usually a blend of coasts and physical geography. Occasionally, I post photos of a shoreline with little geologic or geographic narrative. And sometimes I even post photos of something geologic with only a very tenuous connection to the coast.
A few days in New Mexico left me with a particularly tenuous connection to the coast and the next two posts are a bit of a stretch for Gravel Beach. My editor may object - but wait, this is a blog, there is no editor!
White Sands National Monument is a large dune field in the Tularosa Basin of south central New Mexico. The white sands are gypsum crystals, not the quartz sand we usually encounter in dune environments. The gypsum originated in a shallow Permian Sea that may have resembled the warm Persian Gulf of today. This 250-million year old Permian Sea is a recurring theme in southern New Mexico, one that gets visited again in the next post. Repeated drying up of the sea left thick deposits of gypsum.
These gypsum-rich rocks were buried for most of their history, but were then uplifted and exposed 70 million years ago during the Laramide Orogeny (formation of the Rocky Mountains) and erosion and chemical dissolution carried the gypsum into the isolated Tularosa Basin. The gradual drying up of Pleistocene Lake Otero further concentrated the gypsum and now the winds blowing across the dry lake beds of Lake Lucero and nearby playas carry the gypsum crystals up into the dunes.
Labels: new mexico
Venice Beach lies south of Santa Monica on a barrier beach built between the ocean and the large Ballonas wetlands to the east, the historic estuary of the Los Angeles River. There isn't much left to the wetlands now, since a large portion of them were excavated to create Marina del Rey in the 1960s. And the LA River hasn't flowed out to the Pacific this way since a flood in 1825 sent it south to San Pedro Bay (now Long Beach).
Historically, the river may have been a significant source of sediment for the beaches at the south end of the littoral cell (Dockweiler, Manhattan, Redondo). This source is long lost, but these beaches are now very wide as a result of the addition of large amounts of sand from leveling the El Segundo dunes, building LAX and the Hyperion Treatment Plant, and the dredging of Marina del Rey. The beaches have remained relatively stable, although eventually this material may end up at the south end where it gets sucked down into the submarine Redondo Canyon.
Like Santa Monica, Venice also has a breakwater, but unlike Santa Monica, the beach at Venice has built out and connected with this one (or at least is connected most of the time). Besides the breakwater, Venice also has a large groin farther south near the Venice Pier.
The Santa Monica littoral cell extends from Malibu south to the Palos Verdes Peninsula, shaping the western beaches of Los Angeles. As elsewhere on the southern California coast, sediment transport is generally from the northwest to the southeast.
Historically, the beach at Santa Monica was supplied by Malibu Creek and a number of other small streams in the northern part of the cell. These are streams dominated by big, but widely-spaced, flood events and sediment was probably delivered in big slugs. Development has altered runoff and more importantly, led to the construction of flood and debris control systems that trap sediment before it reaches the coast.
The Santa Monica Pier marks a significant geomorphic transition. To the north, the coast is backed by bluffs cut into a marine terrace composed of alternating marine and alluvial sediment. To the south, the bluffs disappear and the coast morphs into a long barrier beach (although this may be a little hard to see through the overprint of development). More on this in the next post on Venice Beach.
Early pictures of the bluffs show them eroding onto a relatively narrow beach. Perhaps at times in the past they were also a potential source of beach sediment? But the bluffs are now separated from the ocean by the Pacific Coast Highway and a wide beach created decades ago through some major nourishment projects.
An early breakwater - apparently part of a scheme to develop a boat basin (there have been some grand plans for the Santa Monica coastline that never materialized). The initial effect of the breakwater was for a salient (bulge) to develop on the beach behind it, but that feature is barely perceptible now that the breakwater has subsided and the beach has been widened so much by nourishment. The breakwater can still be seen in the aerial view and, if you look carefully, off the end of the pier in the photo below.
Saturday, March 08, 2014
Portage is one of those names that crops up in many different places - but the three that come to mind on Puget Sound (I'm not counting Portage Bay below UW) are all tombolos, or at least were tombolos at one time). All three were places where simply lugging your canoe over the beach berm saved you several miles of paddling in rough water.
One of these is at the tip of the Lummi Peninsula at the north end of Bellingham Bay, where a spit (really just a bar, but that's another story - one I don't know) connects to Portage Island. Another is the passage between Indian and Marrowstone Island, which was closed by a barrier beach until the Corps of Engineers excavated the channel and built jetties early in the 20th century.
The third is this low isthmus that connects (or separates, depending on your perspective) Vashon and Maury Islands. As with all of these, there is always some debate about whether historically there was an open channel, but in general, maintaining a channel in these situations would be difficult, as the beach would tend to close up the gap pretty quickly. There has to be a pretty strong tidal differential to maintain enough flow to keep something like this open (or a complete lack of sediment). That doesn't mean that sometimes storm waves and high tides would not have periodically washed over the top, but that's not the same as a navigable connection unless you're in a kayak and willing to do battle with the logs.
The north side of this tombolo would have been the primary berm since the exposure is greater and there is much more robust beach. The south side lies within Quartermaster Harbor and is fairly sheltered. Typically, in a situation such as this, the wetland that formed in association with the tombolo would have drained to the southern, more protected side. Trails across these features become roads and a desire to maintain access during storm conditions leads them to be elevated and armored. Here, it's still only a short hop from the beach on the north side of the road to the remaining wetland on the south side. And the south side, like any south-facing beach at the north end of an embayment on Puget Sound, is a magnet for anything that floats and blows across the surface of the water. Logs, old styrofoam floats, plastic water bottles, sneakers, tennis balls.
Two weeks ago (I hope readers don't think this blog is live - or even almost live), I was on Vashon to give a talk and had a chance to swing by Dockton, where another small restoration project has just happened. For the "before," check out my post from a few years ago:
Dockton: May 2008
Note that the restoration project is just west of the boat ramp and county park - there is another, larger restoration project just waiting to happen under that parking lot!
The county has recently pulled out the old riprap and excvated an s-shaped channel to capture the upland runoff. The hydrology may be defined as much by culverts under the road (which lies just uphill) as by the original stream network. The result is a small stream mouth estuary - or what will become one. Besides the channel, the beach berm has been reshaped to form a small spit. Waves (what few there are here) and tides will spend a year or two reshaping the berm, but the bulk of the changes from here on out will be in the vegetation and in what ever fauna choose to colonize or pass through. It will be fun to watch.
Wednesday, February 19, 2014
We had a pretty benign January, but it seems like the last two weeks has just been one new storm every 24 hours. Fortunately, many hit hardest at night, leaving us some very pretty days in between the squalls. Early Sunday morning, I took advantage of a lull in the action to drive out to La Push. Saturday night's storm had subsided and the drive across 101 was beautiful with clear patches and a little sunshine and fresh snow low on the hills.
I was on Third Beach by 11:00. The skies were gray - but dry - and the tide was pretty high, but it was a great dose of the Olympic Coast, which is exactly what I'd come looking for.
Third Beach, like most of the beaches along this coast, is a glorified pocket beach. Its shape is largely defined by rocky headlands - that confine the beaches - and the interaction of Pacific Ocean waves with the complicated bathymetry and clusters of sea stacks - that shapes the beaches. Ultimately, this coastline is probably a reflection of the geology -- an assortment of resistant sedimentary blocks (the headlands and stacks) with much softer stuff in between (the bays and beaches).
There's a waterfall at the south end - basically a hanging valley where the ocean has cut landward faster than the small stream can cut downward. The waves had cut into a very high sandy berm near the stream mouth - providing some indication of how dynamic this beach must be. Many of bluffs along here are actively collapsing onto the beach. Some appear to be fairly slow-moving slides, but there was a big pile down the beach that looked like it must have come down both quickly and recently.
The tide was too high and the waves too big to explore safely and I look forward to coming back for longer in nice weather and when the tide is out. But it's days like this when stuff actually happens!
By the time I got to Second Beach, an hour or so later, the wind had picked up (the tide, too, there was little beach to be seen). And by the time I got into La Push, the next storm had fully arrived. I ate my sandwich in my car out at the jetty with the wipers on high and the car rocking in the wind. La Push is worthy of a whole post in itself - several, actually - but it will have to wait for a trip where I can get some better pictures.
I drove over to Rialto Beach, but between the storm, the water level, and all those big logs on the move, I decided against walking north to Hole in the Wall. Next time! It was a very wet drive back to Seattle.
Posted by Gravel Beach at Wednesday, February 19, 2014
I have this peculiar little hang up. If you're going to spend all day in a meeting or a workshop about beach stuff, and it's held within a stone's throw of the beach, you should actually go to the beach. Even if it's only for five or ten minutes early in the morning and there's a high tide and a bitterly cold north wind.
I like the Edmonds waterfront. I guess that's because despite its developed setting, there are still beaches and most of them are publicly accessible. It's a far cry from the large spit that once separated a big salt marsh from the Sound (map is from 1872) - the marsh that's left is a small remnant of the original and the barrier is segmented into a few artificially confined pocket beaches - but I wish we could figure out how to do this with some of our other small town waterfronts.
And here are a couple of earlier posts from April 2009, when it wasn't quite so cold as this Monday morning two weeks ago.
Monday, February 17, 2014
I was up in Oak Harbor again for Sound Waters (Saturday, Feb 1st), which meant that I had a few hours in the afternoon to work my way down the island. I spent much of that walking below the bluffs south of Swan Lake, turning around when I got a little south of Fort Nugent Road (which is how about how far I got walking north from Hastie Lake (February 2012) on a comparable Saturday afternoon two years ago).
This is a wonderful stretch of 200-250' bluffs, the bulk of which are sandy units that probably belong to the Whidbey formation (lower) and Vashon advance outwash (upper). As noted previously, wind erosion is significant along here and the homes along the top are built among the perched dunes where this windblown sand collects. The dunes are largely obliterated by the development, but the sand still collects on decks and driveways.
I wish I knew more of the story of these two concrete structures. The one on the beach must have come down fairly recently, although I haven't been down here in a long time so don't know for sure. On Google Earth (image dated 8-25-2011), it is already on the beach. There's another hanging on the edge a short distance north and destined to come down soon. From their proximity and general similarity, I assume they are a pair - are these observation posts of some sort associated with the island's military history?
Monday, January 27, 2014
Two posts back, at Lake Quinault, I noted that beaches are easy to make. But that doesn't mean that they are simple, that they are all the same, or that they fail to exhibit an amazing amount of small-scale spatial and temporal variability.
A late afternoon walk at Golden Gardens found lots of stuff happening - much of which will be erased within a few tide cycles. And replaced with something else.
Waves on a rising tide will sometimes leave a swash bar like this sandy one lapped up onto the beach face. Perhaps the band of gravel at the water line was the coarse lag left behind when that rising tide pushed the sand up the beach. Seepage from the beach face formed complex alluvial channels on the lower beach face. A high tide gravel ridge to the north recorded the story of strong southerly waves during a recent high tide.
Meadow Point is a barrier beach that curves sharply and there are big differences as you walk from the sandy beach on the south to the gravelly one on the north. By the way, this northern beach was probably always coarser than the southern one, but the current pattern was reinforced by the gravel that was added in the mid 1990s to address the chronic erosion of the northern shore (possibly attributable to the loss of sediment from the north after the railroad was built, but that's another story).