Friday, July 6, 2007
Normal Faulting is "Normal"
Mathematically, an action is normal, when it is perpendicular to that seen previously. But for faulting, Normal not only is similar (a block falls perpendicularly to the earth's surface), but this is the NORMAL action. Most faulting in the interior is in this category- only at large tectonic events is there significant thrusting or REVERSE faulting.
The cliff walls at the beach in Bush Point Bay (between Lagoon Point and Bush Point S32 T30N R2E)show normal faulting, but the crack shown above could have such small displacement downward, that it would be classified as a FRACTURE. Notice how the vegetation has masked the appearance of the fracture as it continues to the upper left. This is also normal, since there would be percolation of water down along the fracture surface (the opposite of compression, where movement of fluids is reduced). This category of faulting occurs for the case of the crust (or shallow layers of the ground) being under tension (extension could also be the classification).
This is of major mechanical importance, since the earth's crust moves only in three ways or is in three categories:
1. Under EXTENSION, or being stretched or pulled apart (Normal);
2. Under COMPRESSION, as with crushing or shoving (Reverse, or Thrust); and
3. Under SHEAR, as two opposing forces moving alongside each other- TORSION, or twisting, could create a similar effect. Faulting in this category is hard to see, since vegetation or rubble on the surface obscures the line of shear (Lateral faulting).
Wednesday, July 4, 2007
E-W fractures indicate orthogonality with strong N-S stressing of mid-Whidbey Island
A Close-up of Thrusting on Whidbey Island
There are thrust planes found in the cliffs on the west side of W.I.; these are undeniable, as analyzed in previous reports in earlier submissions. However, whether they are predominantly the work of glaciers, to the exclusion of other tectonics, must be demonstrated.
The photos above show that there are a fair number of small thrusts near the Hancock Lake, which is within two kilometers of the well-documented Fort Casey-Ledgewood-Baby Island NW-SE still-active fault zone. Since these change their appearance with the annual slumping and retreat of the cliffs near Hancock Lake, this raises some doubt about their incipience and magnitude.
One large thrust plane has not ameliorated with the years (shown in photos), even though several other large sheets noticed nearby have disappeared. This is shown in the cliffs just south of Hancock, and I have explained the entire phenomenon as due to the significant scarp there. Driving on the hiway 525 roadway near Greenbank, one can see the scarp, as the automobile chugs down, climbing it going south. This scarp is on the narrowest part of the mid-island, springs occur there, and the thrust plane is on the immediate south side of this scarp in cliffs.
I have suggested that one of the glaciers pushing south, rammed against this scarp, forcing the top layers to slide to the south- giving the appearance of a thrust sheet. Since the thrust plane is almost horizontal, this conjecture still seems reasonable. The fact that some of the associated thrust planes have disappeared over the years introduces some doubt. This disappearance indicates that whatever occurred was not of large lateral extent (except for the one plane remaining).
One confusing occurrence is that of cross-bedding in dunal sands, which sometimes appears in cliffs near by. Inter-dunal zones, which may occur above and preceding later dunes look like thrusts. One may sort this out, by looking at fractures- and not the cross-bedding. I take it that parallel fractures (three or more) are not inter-dunal intervals, and these were noted in the report for Ebby’s Landing. Coastal dunes are voluminous in the cliffs, and even occur in the island interior; one such is on the east side of East Harbor drive, near Sands Lane- falling continuously on the shoulder. Some of the photos above may appear as cross-bedding glimpses. But the buckles are undeniably due to compression and thrusting. The question remaining is: since these buckles are very near the bottom of Till, this should strongly suggest that glacial sliding from the north has produced them.
Notice the one layer which is buckled, with the bed riding over itself to the north (all of these photos and comments are for beaches running north to south, on the west side of the island). This is opposite what should occur, for a glacial sliding over the upper layer causing thrusting toward the south. Rather, it appears that the force has come from below, forcing the bed to ride over itself.
Adding to all this mix, one photo shows that there are orthogonal fractures, running E-W in the cliffs. This would occur with breakage perpendicular to the dominant stress- which was N-S for the mid-glacial period (not the latest). Although not conclusive, this throws the argument to the side of glaciers being the dominant entity in this 50k ybp time.
Tuesday, July 3, 2007
EARTH LORE Magazine- a weekly Blog of True tales of the WEST and its Earth Science. Local earth happenings are shown, with photos, how the Blue Planet reacts to MAN's desecrations and FIGHTS BACK (on its own terms, and its own time schedule).
Weekly Renditions are made by the following Contributors:
Penny Scholten, geologist and outdoorswoman;
Dr. Chris Oravec, English at heart;
Harold L. Overton- earth critic and scientist; and
Col. Glenn Wasson, a Robert Service devotee’
English Subtleties (not Sub-Titles!)
A Turkish friend recited to me that even though she had a PhD in English, she still could not easily distinguish between the sounds Leather, Leader, Ladder, Let Ηer, and Lather. Those of us associating with the Ideas behind the sounds have no difficulty, but this illustrates the chore of getting Meaning from sound (with special difficulty for homonyms and synonyms). The following limerick emphasizes the closeness and subtleties in similar sounds in the English language which widely diverge in meaning.
My Rain, Maurine, lies Mainly on the Moraine
Although I was hardly a marine
Raising Merinos was no Mean
Task, for an uninitiated Teen.
I would promptly rise at Dawn
Performing duties, any Moron’d
Smilingly have a daily Go-On.
Wiping off the fresh Meringue,
Barely hearing the Daily Harangue,
Merry-No! while I watched the Gang.
I would longingly gawk Marina,
Keeping my thoughts on the Antenna
For the Lead in my Radio-Galena.
I have progressed from Merry-No
Earning my ring from the U of O,
To studies of the ol’elevated Colorado.
The Plateau, with its high Moraines-
Stoutly above the Western plains-
Is now the object of all my Brains.
Scarcely the same as ol’ Grey Mare, eh-NO?
Gladly the Cross-Eyed Bear- OH!
To forfeit the theme for this Spanish Merino.
You can see the trend for “some Mo’rain”
Is easily corrupted- causing Pain
For any (late) Verbalizer- on the wane.
Harold L. Overton
Sunday, July 1, 2007
Anomalous Rocks on Whidbey Island
WI is mostly covered with young glacial layers- mainly till and stream wash deposited in the last 50,000 years. Occasionally, there are outcrops of older rocks, such as at the Deception Pass area, just near the bridge, and surrounding the hiway 20. These rocks are named Metasediments (sediments which have been metamorphosed- squeezed at depth), and they are from the Mesozoic Era and older which outcrop regularly to the north and on the San Juan Islands. This means that they are older than 65 m.y. (Cretaceous and older), compared to the rest of the island- which is no more than ¼ million years of age.
A small outcrop of these older rocks occurs anomalously at Rocky Point- which is a section of west beach, on the Naval Reservation, in Section 21 T33N R1E (anomalously in the sense that they are surrounded by very young glacial Pre-Stone with age less than one million years)- see the above photos. The stone has been shoved up and laterally by shearing in the earth- the metasediments are being carried between two faults running about 120 degrees from north (almost SE-NW). This means that they are dragged by shear similar to that which caused them to be metamorphosed in the first place. The important questions to be asked here are as follows:
1. How and Why are the rocks being forced to the surface, when the only obvious movement anywhere nearby was that at the Deception Pass, where the continental hard rocks have been shoved almost due west, referenced to the Pacific plate rocks? Incidentally, this large faulting with several thrusts has created the San Juan Islands (in layers stacked on top of each other-but out of regular sequence), and the fault surface can be seen just outside of DP Park on the east side (where a E-W vertical wall or scarp occurs).
2. How can these heavy rocks (relative to the light weight till) be floating at the surface of the earth; if anything, they should at least sink in the soft sediments surrounding them?
3. How can we be sure that the metasediments are not connected with similar stone at their base? We can see that they protrude into the air, and are obviously disconnected on the north and south sides- but there is one side unseen and not open to inspection- the bottom. Why could not the metasediments curve upward from a near horizontal position deep in the earth and gradually bend and protrude vertically?
Analysis from the Photos
First, if these layers are being dragged along a 120 degree fault plane or shear surface on the south side (and the LIDAR map shows this clearly as a fault), then they cannot be connected to the original basement there. This means that the beds, if they are curving upward to a vertical expression, cannot curve upward from the south- since this is the discontinuous side. The fault plane on the north side would tell the same story, but this fault is not shown on the LIDAR map. This fault is only seen in the cliffs at the northern contact with the glacial deposits, and this is the weakest part of the analysis.
Second, the outcrop has a visible fracture running about NW-SE in one of the photos. This is seen as a large break in the rock with vegetation, a cavity, fractures, and seepage. This has remained damp over the 10 years I have visited it. The entire outcrop, which is about ½ km from north to south, has vertical bedding consistently oriented toward the 120 degree direction (which is the orientation of the LIDAR fault). It seems reasonable that the fault is left lateral, which results in the outcrop jutting into the sea on the north side, since all faulting measured by me for the north side of the island are left-lateral (2 cases). There are no other vertical beds anywhere on the island- even at Deception Pass. The NW fracture is the type occurring now on the island, and this indicates that the outcrops occurred first.
Thirdly, Rocky point is some 8 km or more from similar rock at Deception Pass, and not likely to be connected in the basement. There are the Silver Creek and Mariner’s Cove faults which I have inspected, which intervene in that distance. There is nothing nearby which indicates a connection- Rocky Point is anomalous! We still haven’t proved that Rocky point metasediments are not connected in the basement (subsurface) with others of its type, on the north side. But I hope to show the larger picture for Whidbey Island- to indicate that small events may sometimes be rationalized by looking at what happens regularly nearby.
CONCLUSIONS;1. The Rocky Point outcrop is anomalous, in that it is not connected with anything near at the surface- it is Mesozoic or older, contains metamorphosed sediments (metasediments), it is oriented in a direction of bedding pointing 120 degree from north, and it is faulted at least on the south side by a similarly-oriented fault as seen by LIDAR mapping.
2. The RP outcrop is surrounded on the ground surface by young, soft Till and non-indurated or non-strongly cemented sediments- it is anomalous in terms of strength, position, and orientation (except for the parallel faulting on the south side).
3. RP is a true point, meaning that it is resistant to storm erosion and juts into the Sound. It is increasingly covered by storm wash, as noticed for the ten years I have observed it (the sea is rising near 1 mm/year as measured by an independent geologist, near Admiralty Head).
4. RP is fractured in its mid-section by a NW-SE, or thereabouts, opening- which has an obvious accompanying seepage. This rock is the highest of those remaining- indicating that it is being shoved upward from below (which would be a reason why the metasediments are floating). If this is correct, then it is connected with the basement in some way- but not necessarily with the original neighboring metasediments.
5. Since the entire outcrop aligns in the common direction (120 degrees from north of ½ km aligned rock) it is likely that it is a separate block broken off from the original bedrock and carried along the active shearing zone. It must be sitting on top of other basement- with a low probability that it is connected with its original neighboring rock.
6. The orientation of 120 degrees from north, when extrapolated to the east side of the island is coincident with the location of Eerkes spring (which creates road breakage and can be found by looking for patches and a low place in the pavement on Torpedo Road, just NE of the Naval Commissary). IF these are connected in the subsurface, this indicates that the Rocky Point fault is of great significance. The orientation would connect with an obvious large and active fault at Utsalady Point on Camano Island, which can be seen on LIDAR decisively.