Wednesday, July 30, 2008
A small pocket beach, trapped between a headland of historic fill and the breakwater of the Cap Sante Marina. The original shoreline was several hundred yards to the west and this whole area was the site of a large mill and piers covered with dimensional lumber. The lower intertidal is covered with the remnants of that history, though it is scheduled to be cleaned up in the next few years.
Sunday, July 06, 2008
There is something ominous about this place - huge soft flats, huge tide range. No wonder they post warnings about going out on the sand. The beaches are pretty minimal, at least as far as I could tell, in part because the railroad grade and the highway are built right along the edge and in part because the mud and silt are so thick, they pretty much come up to high tide. Maybe there was a beach once upon a time, but now it's buried under all that mud.
We passed along this shoreline four times, twice by car and twice by train, but never timed it right to see the tidal bore - though apparently it hasn't been the same since the bottom dropped out 44 years ago. Too bad, bores are limited to a very few places in the world where tides and topography conspire (Wikipedia).
Friday, July 04, 2008
Seward - another case study in geological hazards. Most of the town is built on the alluvial fan at the base of Lowell Creek. That's good because at least some of the town is out of reach of tsunamis. That's bad because there is no reason to think that the alluvial fan stopped growing when they built the town. As matter of fact, in 1917, Lowell Creek washed out pretty much everything in a big swath along Jefferson Street. But in the 1930s, the clever engineers solved the problem. They put the creek in a tunnel and diverted it to one end of town. I looked at the hole the creek goes down. It's not very big. A debris slide or a gully washer with a few big rocks and trees, and the hole is plugged. The overflow will go right down Jefferson Street, just like in 1917... (okay, so I'm being alarmist, I'm sure those clever engineers anticipated this back in 1930 and planned accordingly).
In 1964, most of Seward's shoreline slid into Resurrection Bay - carrying rail yards, fuel tanks, trains, you name it. The tsunami cleaned up some of the mess. Subsidence repositioned the shoreline. Now there's a strange beach with old piles and debris sticking out of it. The shoreline is now a two mile long RV park and a nice public trail and lots of tsunami warning signs. The Kenai Peninsula is one big study in how quickly beaches can re-establish after mother nature cleans the slate.
Thursday, July 03, 2008
In 1964 a large subdivision, perched on the Bootlegger Cove clay and within sight of downtown Anchorage, collapsed in a heap onto the shoreline of Knik Arm. Earthquake Park marks the site and the coastal bike trail wanders through the slide itself. There are sag ponds, hummocky terrain, a clear headscarp, all the classic signs of a big landslide, but no obvious evidence left of the homes. The shoreline is marked by a marshy beach and lack of any clearly defined bluff. I have no idea where the modern shoreline is in relation to the pre-1964 one, but apparently the slide extended well out across the beach.
I remember seeing pictures of the destroyed homes in magazines as a kid and later in geology textbooks. It's fascinating to see the real thing. I expected more vertical relief - it's a pretty subtle feature compared to what I'm used to on Puget Sound - though it clearly covered a lot of area. It really spread laterally as much as fell downhill.
This beach is west of Anchorage, near where Cook Inlet splits to form Turnagain Arm and Knik Arm (this beach is on the latter). The tide range is large, the silt load is huge, and the beach was sort of weird. High sandy-gravel bluffs. Sand ripples on a gravel beach with a thin coating of silt on the sand. The ripples appeared to be around mid-tide and I suspect they reflect the role of fast tidal currents along the shore of the point. The silt seems inevitable given the muddy water.
This beach is particularly impressive when a 747 takes off to the north.
Wednesday, July 02, 2008
For a blog titled Gravel Beach, this particular post is weighted much more heavily to the gravel than to the beach. But given that most of the gravel on Puget Sound began in the mountains and was transported to the Lowland by glaciers, it seemed some good glacier and dirt pictures were appropriate. Even if these happen to be from Alaska.
Tuesday, July 01, 2008
A gravel beach with a view across Cook Inlet of Mt. Iliamna. The backshore is wide - extending out in front of the base of the bluff (more place to park RVs). This is another place where I would love to know how the 1964 subsidence affected the shoreline and how the beach responded in the following years and decades.