Earth Movements on Whidbey Island (Just to the West of Camano): 03-04 Summary
FAULTING (see attachments on the website:
www.geocities.com/overtonharold/ )
The Baby Island- Ledgewood- Admiralty Head fault is our most certain fault. It runs NW-SE, and can be seen and sampled just off the coast of Saratoga Road (adjacent to Baby I.). It protrudes into the air with a set of small hogbacks running 130- 135 degrees from north, and the rocks are obviously hardened in their exposure- appearing to be Pliocene in breaking strength. It is Pleistocene, since it cuts that age of sediments, and this accentuates the fact that compressive stresses may increase the strength and hardness of sediments. Although the fault is of lengthy expression (Admiralty to Baby Island), it is hard to see it in the interior of the island, north of Greenbank- it may be related to the occurrence of springs and seeps near Nettle Road, which has a drainage running NW-SE.
I believe that the fault is still active, based on the road breakage and slumping at Ledgewood; but there is only one concrete slab indication that it is left-lateral, and the main observations support the conclusion that it is compressive and causing uplift at selected locations like Admiralty Head (it could still be left lateral).
Other faulting on the main body of Whidbey Island can be called minor, and some of these are noticed in the cliffs. One of these was predicted based on changes in the water composition of water wells. This is the El Capitan beach fault, and it was noticed first, by the anomalously large amount of K compared to Chloride in the water. Its visual expression is the only set of clean cliffs south of the Borgman Road access. There is a seep, angular block insertion into fractures, and uplift in the sediments in the cliff.
The fault which has been most studied by our group is actually two faults or more, surrounding the Rocky Point exposure. There is a lesser observed fault on the north side of R.P., and the greenstones and metasediments are currently dragged between these two movements. The fault runs about 130 degrees from north, and has been exhumed by the USGS in a trench for measurement. It has a displacement of the main fault trace, to the north as shown by LIDAR, of about 330 feet- which would indicate that it is being sheared north-south at about 1 cm/year (since is it is seen in glacial till of less than 15,000 years age). Both of these faults surrounding the Rocky Point continue on to the SE, showing up in asphalt breakage near the Naval Commissary, in the formation of Tombolos or fossil tombolos at Polnell Point and at the seaplane base south of the commissary. The Rocky Point exposure is uplifted in the middle causing fracturing- the greenstones appear to be detached from their original bedrock, since one end protrudes in the air and the other end is parallel to the faulting direction.
There is a general tendency for the faulting to become more eastward in expression as the faults are explored on the north end of the island. The Silver Lake and Creek run about 110 degrees from north, as does the El Capitan fault- compared to the SW-NE faulting at Baby Island and at SW Maxwelton Creek (toward upper Cultus Bay). This hints that the NW-SE fault trend is the result of the interference of the Pacific Plate moving northward relative to the North American plate running westward. The vector resolution of two stresses running perpendicular to each other is a diagonal between them, with exaggerated importance of each stress direction as the main thrust becomes nearer to the fault being observed. This diagonal trend would be the case when each stress is of similar effect (magnitude). However, the Pacific plate main thrust is west of the San Juan de Fuca expression, and there are spreading zones west of the Vancouver Island coast (locating the westward edge of the sjdf plate, by thermal vents), indicating that the Juan de F. plate is still moving east, far west of Whidbey Island. It is still possible that the Pacific plate stresses could lurch into the JdF. zone if the two movements are intermittent. However, the north movement has to be significant, compared to the east movement of the JdF plate, and one would not think that an occasional lurching would produce the strong thrusts noticed on the south end of Hancock Lake. My revised thinking (2003) is that those S. Hancock thrusts are a result of glacial sliding, and that the north thrusting caused by Pacific Plate lurching is overshadowed by the much larger movement during the Pleistocene (due to glaciers).
The only significant evidence of N-S thrusting due to occasional Pacific Plate lurching is that of the displacement of the Rocky Point fault as noticed by LIDAR. There are several N-S fractures which could add weight, including the one on the seaplane base Tombolo, and to the fractures which die out looking upward on the cliffs (as opposed to glacial-induced fractures which die out with depth).
My tentative conclusion about all this is that the N-S fractures are just now being formed, as the JdF plate moves under the continent and dies out (not yet), while the Pacific plate is getting closer to W.I. and beginning to assert itself.
FRACTURING (see 2nd attachment, in website):
Fractures may be seen at many orientations and locations in the cliffs, so that one cannot use them for specifics; however, the pattern which they make when seen for multiple entities is useful for determining the regional stresses causing them. For example, at Deception Pass area, they are mainly down to the north on the south side of the bridge, and oppositely on the north side of the bridge. This indicates a change of stress direction at the Pass.
Fractures may be seen to be related to Alkalinity in the wells which are near significant fractures (see attachment 3). This is the case with South Whidbey, where water wells show that there is a geochemical anomaly around Cultus Bay (see the alkalinity map on the website. I postulate that the connection is with HCO3, which is the most significant part of alkalinity in water wells. When rainfall finds open fractures, it develops a faster path of recharge to the water aquifer, and on the way creates the following reaction:
H2CO3 (carbonic acid in rain) + CaCO3 (calcareous cement in sediments) > 2HCO3 + dissolved Ca++.
Consequently, when recent fractures are created by stresses in the earth (by extensional forces), rain will increase the HCO3 in nearby water wells, and will give a signal that fractures and loose sediments are building up water pressure. This would be accompanied by a rise in water table, providing there is not excessive usage of well water. A result of this could be slumping, which causes large amounts of earth to spall off cliffs, lubricated by the rapid increase of subsurface water. Since this is the case with hiker Cronk's water well, we will use him as a test case to see how long this signal occurs before a new slump happens. The south coast has a history of 33 years/slump (somewhere, not necessarily in the same place repeatedly), so Don has a respite of up to 33 years before he loses his back lot.
2004 findings:
Fracturing, cont’d
1. Fractures should only be used to generalize about earth stresses- whether there are compressive or extensional local earth stresses. A fracture, as I use it, must be confirmed as part of a set of parallel cracks in the rock to be considered more than a random expression of exfoliation, jointing caused by differential thermal expansion, ancient weaknesses in the rock caused by fossil stresses, and gravity effects (incipient slumping, recent earthquake influences, and man-made cracks caused by blasting).
2. Fracturing should be used for stress information, only in conjunction with other stratigraphic or structural findings to confirm a pattern- e.g. compressive as seen about a fold or anticline, or extensional as seen near normal faulting, springs, and drainages.
3. Regional Fracturing, such as found in the surface of rock outcrops, may be used to determine local anomalies; e.g. whenever there is a well-defined regional trend, such as SW-NE over much of the Colorado Plateau, the local departure of parallel fractures from this orientation will indicate a local anomaly.
4. In the cliffs of Whidbey Island, a set of parallel vertical fractures may indicate the local stress state now. At Ebby’s landing, over a course of 5 years (observed by me), as erosion proceeded, small thrusts in the cliffs eroded away, leaving nothing in their place in the sediments previously hidden behind. These likely were caused by the recent glacial compressive forces as the ice moved downhill, causing local disruptions in the soft sediments.
5. A single fracture should not be used for any specific or generalized information. Further, fractures located vertically above others should be treated differently from those which are parallel horizontally (at roughly the same elevation); e.g., at the suspected location of the Baby Island fault in the cliffs across the Holmes Harbor (NW of the B.I.), there are two fractures parallel to each other in a vertical separation. The lower one has an X fracture, with a small lens of sand along the orthogonal part (down to the north), indicating secondary fracturing. The set of parallel fractures indicates the present stress state, but the down-to-the north has caused some relief to the stress. There is no displacement noticeable, but the parallel down-to-the south fractures are not what would be expected by ice moving south- which is what has transpired here. Rather, ice would be expected to cause the fractures to rise to meet the direction of ice movement (up-to-the-south). The conclusion in this case is that present stress may have caused the fractures, but the absence of displacement indicates that a fault is not present (but may be nearby).
FAULTING
Seismic may indicate that faulting occurs on a straight line trace at the subsurface, but we have not found this always to be the case at the surface.
1. At the NW-SE fault trace proceeding from Maxwelton Village to the “hook” at the north end of Cultus Bay, the trace proceeds SE from the village along the south Maxwelton Creek, but then it jogs to the north in the portion near Swede Hill, indicating that Swede Hill has uplifted since the original faulting. This is valuable information, since it indicates that the uplift can be timed- it is post-faulting.
2. At Cultus Bay, there is an anomaly in the faulting; although the NW trace can be seen on LIDAR and on the geographic TOPO, the perpendicular change in Cultus Bay indicates that there are two orientations- NE-SW as well as the orthogonal Creek orientation.
3. Lateral faulting on W.I. is sinusoidal in expression- that is, it is compressional at times and extensional at others. The fault expression at Baby Island, which is undisputable, is in the nature of small hogbacks just 100 meters distant from a normal dropping on the west side in the concrete barricade. This expression of down drop is disputed by the local inhabitants- who have a pecuniary interest in maintaining property values. They maintain that the down drop in the bulwark was put in the concrete originally, ignoring the fragmentation of the boundary concrete. However, they pointed out that there is a junction of two separately-poured concrete sections, and indeed, when one looks at the base of the bulwark, there is an old wooden separation junction. This uplift on one side of the fault appears to be the case for Admiralty Head also. It is possible that some of the suspected drop at B.I. (19 cm) is artificial, but there are other indications of down drop on the SW side, other than the concrete separation. There are sets of parallel fractures, which are wider at the top, than when they occur lower in the concrete- this indicates extension on the SW side, or settling as one approaches the concrete breakage.
4. The creek orientation seems to be a better method of finding linear faulting than does the LIDAR. Good examples include Silver Creek- running 110 degrees from north, S. Max Creek, running mostly NW-SE, the small drainage north of Loganberry Farm, running NW-SE, and the NW-SE drainage north of Mutiny Bay.
5. Ιgnore creeks or drainages running N-S, since these are expressions created by the scouring and carving made by the dominant glacial movements. Only when drainage crosses the N-S scrapings, can it be considered as happening since the glacier period.
6.
ALKALINITY MAPPING
Extensional fracturing can be considered to have opened the earth to faster penetration of rainwater. According to the relation:
H2CO3 (carbonic acid in rainwater) + CaCO3 (limy cement)>2 HCO3 + Ca++ ion.
That is, whenever slightly acidic rainfall (regardless whether man has instigated it or not) falls on the ground, where it is easier to penetrate new fractures, the end product is increased alkalinity of the ground water.
This is shown on a map of the south end of the island (see the alkalinity geochemical map on the website), where Cultus Bay has formed (perpendicular to the normal trend of NW-SE faulting), and where the contours of alkalinity/chloride in ground water show parallel-ness to the orientation of the bay.
Past history has documented slumps occurring in large amounts on the south end of the island, some as large as 10 acres at a whack. This would be expected to have been caused by the SW-erly storms, which exaggerate erosion. However, the fact that the slumping occurs on the SE coast more than on the SW coast at Scatchet Head, and that the faulting is peculiar there indicates something more than storms.
The slumping, which was predicted to occur on one of the hiking member’s lot, was not predicted in terms of time, but in space; this rate is unknown, since the scanty data used to predict the slumping was only 4 occurrences in a century. This suggests a rate of occurrence of something like once every 1/3 century. The hiker’s lot experienced slumping within 6 months of the prediction and now his neighbor has slumping also. The water well chemical analysis used to make this prediction was based on the occurrence of excessive K/Cl and alkalinity/Cl, in a well used only by the lot owner. There was no history of measuring alkalinity/Cl over a time interval, so that the buildup of HCO3 with time is unknown.
The extensive peat layer was used to understand the structure and stratigraphy at Scatchet Head and Cultus Bay, to try to understand the structural and geochemical anomaly there.. This peat increases regularly in elevation going south from the village of Maxwelton, but falls in the tidal zone going east toward Sandy Hook. This creates the Scatchet Head, indicating a compressive- upward feature. There are small grabens at the village of Scatchet Head, indicating a change of compressional to extensional stresses. All of this together yields the following conclusions:
1. Scatchet Head is not only recent, and a faulting compressional anomaly, but has an incipient anomaly running perpendicular to the main faulting.
2. The slumping is being exaggerated by fractures running perpendicular to the main trend, and is preferentially spalling off in a NE-SW direction.
3. Effort should be made to determine the nature of this NE-SW extensional anomaly, since this is seen nowhere else on the island. However, Polnell Point, Bush Point, and Maylor Point- Seaplane base are compressional anomalies (bulges) running NE-SW also.
Geochemical Mapping and Seawater Intrusion
There is a valuable store of water well and chemical analyses available in the Island County Health Department files; this has been accumulated and organized by a hydro-geologist, and is reflected in the previous maps and analyses for faulting and anomalies. Since the wells are mostly drilled to similar depths, and reflect meteoric water which has been influenced by glacial sediments mainly (before the advent of man), this is an invaluable source of data for geochemical analyses.
Geologists are likely to ignore anomalies which are vertically oriented, particularly when they are trained in conventional stratigraphy- which states that fluid paths for water and oil are dominantly lateral. It is my experience that fluid paths are mainly vertical for the long term- that is for times longer than a man’s life.
The fact that oil has been found around vertical salt domes, vertical flexures in the earth, near vertical paths such as large normal and thrust faults, and even in vertically-oriented dikes and protrusions gives strong hinting that vertical paths are the preferred locations for vertical fluid movement for these anomalous areas.
Water may be moving laterally in normal areas, but for anomalous areas it can be suspected to move otherwise. This is the case for geochemically abnormal zones. It has already been shown for W.I. that faulting can be located by using abnormal fluoride and potassium concentrations. These ions are normally measured in well water, and found to be < .2 ppm for F and < .2 for K/Cl, whenever conditions are normal. Both of these ions are very mobile, because of their small hydrated ion size and valence of +or- 1. In the earth, ions tend to move in the direction of decreasing concentration, opposite to water, which moves not only vertically downward due to its heavier weight than vapors in the soil, but toward increasing salinity due to the osmotic effect. The saltwater intrusion problem may be better understood, if it is admitted in advance that it is better treated as a geochemical entity. If one is determined to make a classification, rather than an analysis, then the use of stiff diagrams and Pacific Island Ghyben-Hertzberg portrayal (hand-waving in the case of Whidbey, due to the many separate cells created by the 9 or more significant faults crossing the island) is as far as one can go. However, the use of mathematical treatment of the variation of ionic concentrations will admit much more. To use geochemical mapping, one must look at the assumptions, which are inherent in the use of ionic concentrations: 1. For a particular region, such as Whidbey Island, there is geologic history which will determine the average or normal background of the chemical concentration and type, dissolved in water. In the case of W.I., there are volcanoes to the east, which released fluoride and acidic waters which reacted with rock already present. The sea itself was present over the stratigraphic column at times and at other times the area was covered by fresh water. Both of these types of water would have left their contents in the sediments (now Pre-stone). 2. Volcanoes belch acidic waters, which may be hydrochloric, sulfuric, or hydrofluoric (among others). Consequently, one may use anomalous F, K, or SO4 as reaction products from the acids. The presence of NaCl, CaSO4, & F is derived from the acids reacting with host rock, in these cases, e.g. HCl + sodium, oxides in rock > H2O + NaCl
This shows how ocean water increased in both salinity and volume, through geologic time, by vulcanism. However, if one uses molal balances to determine the sea water salinity, one finds that the water would be much more saline than now exists, if vulcanism were the only method for dissolving salts in the ocean.
Only F from vulcanism is valuable for anomaly location, since Na and Ca are common in ground water, with wide variations. However, K from igneous rocks (orthoclase, later illite, and K-clays) is a good indicator, due to its small hydrated ionic size, large solubility, and simple valence.
3. The upward movement of components dissolved in water, due partly to their increased solubility in thermal waters, is in no way an indication of the movement of the water host. Ions will move in the direction of decreasing concentration, even the reverse to the direction of the liquid phase. However, the mechanical movement of water (hydraulic-pressure induced) will overwhelm the tendency of ions to move against the stream. Only if the water is stationary will the ionic movement be noticeable. Diffusion is extremely slow, but osmotic changes are relatively rapid. I have witnessed the changes in groundwater around a well bore as oil is produced in a short (less than a year) time, when there were strong pressure changes A way of estimating the mobility of ions is to measure the ionic potential- Z/r (atomic charge/un-hydrated size); this is a measure of the hydrating ability of an ion (attraction to water- which is attracted to the ion, but is restricted to being incorporated about the available surface area).
The hydration of ions, which is partly determined by the ionic potential, is high whenever the ratio is high, so that Ca and Mg move with difficulty through the fractures in rock, whereas Cs, K, and Na move easily (hydration or incorporation of water about the ion makes the overall size of the ion larger). Notice that K has a larger atomic number (19), compared to Na (11), and this is primarily the reason why its ionic size before hydration is larger. The charge density of Na is larger however, since the charges are spread over a smaller area, hence the hydrated size is larger (charge density is larger), and it hydrates with dipolar water more than with K. One may reflect how KCl is prescribed for heart patients, rather than ordinary salt, because Na hydrates more than K, and causes an incorporation of water in the human body. A map on Cs would be the best map for tracing anomalous water contents, but this is rarely measured. Lithium and arsenic are good indicators of warm water movements, whereas fluoride and potassium are mobile at any temperature. K & F ions are more available, similarly to Li & As, whenever thermal waters introduce them from depth either from the weathering or dissolution of granites.
Analysis of the Seawater Intrusion Problem
1. Before man begins to pump water from a well bore, the water and its contents are in a state of near-equilibrium with surrounding rock. The original water should be measured for its contents, to find whether there has been movement of ocean water into the zone which is to be produced.
2. Since both Na and Cl are dominant in seawater, and they are very mobile, the ratio should be calculated for the original water (chloride is essentially non-reactive with whatever the rock has to offer, hence is an excellent reference- to offset dilution, concentration or other errors of measurement). This ratio is .55 for ocean water, and widely varying for rivers, since the dominant ions are Ca and Mg in fresh water, reflecting the rock over which the streams drain.
3. The likely circumstance for well water is that water will be hard- that is the cement holding the rock together is being dissolved under the influence of downwardly-moving meteoric waters (acidic). Volcanic areas will yield softer waters, as will dominantly silicate rocks. Man prefers to drink water which has some mineralization- about 200 ppm, but not over 1000.
4. If the anomalous water is found to be soft with a ratio near .55 for Na/Cl, then the sea is already exerting its influence. However, if it is found that K/Cl is > .2, or F is greater than .2 (using consistent weight units), abnormal salinity can be suspected as being fault-influenced. Abnormal K or F would be treated differently than the case for simple seawater intrusion.
5. Faults connected with the ocean will allow ocean water to move toward the well, whenever the pressure is reduced by pumping- if the well is near the shoreline and contents are marginal, the well should be abandoned.
6. Whenever a well near the shoreline produces water which has anomalous contents (> 500 ppm), the ratio of Ca/Cl should be calculated. Seawater contains only about 1/10 of the tds (total dissolved solids) as Ca+Mg/Cl, so for those compounds in excess of about 50ppm Ca+Mg with Na and Cl low, the water is not seawater. River water has influenced groundwater, in this case, containing dominantly hard components. Glacial sediments, such as those in old streams from melting ice, will have excessive Ca+Mg compared to Na.
7. Anomalous water, or that having tds> 500 ppm, is likely vertically-moved water, if it has an excess of K, SO4, HCO3, F, or other strange ions. The presence of SO4, since this ion does not move across formation boundaries, is an indicator of large fractures, faulting or chemical reactions occurring locally. Peat beds, iron compounds, and evaporative sediments would be sources of this compound.
8. When the well is more than 2 km from the coastline, excessive K or F (faulting) will not indicate seawater intrusion- the bitter or iron-flavored water may be tolerated, and expected not to become much worse.
9. When the well is excessively alkaline (bicarbonated), this produces a bubbly taste, and 1000 ppm could be tolerated. This case is not ominous, even though the salinity is large, but it may portend slumping if the well is near the beach.
The next worse case, compared to excessive salinity, is that of sulfate and iron. These will stink and stain, and create unsightly water. Although seawater is high in SO4 (>.14 for SO4/Cl), this ion does not travel easily through fractures or faulting. It has a large charge and size, and is filtered by clays and shales. But it is attacked by bacteria to produce the stink, particularly in water heaters, and it has an unpleasant taste. This can be treated by filtration or membrane (osmotic) separation. Excessive Fe or SO4 may occur around peat bogs or mineral deposits, but is not likely an indication of seawater intrusion..
In summation, the ratios of Na, K, Mg, Ca- all cations, (c/Cl)- should be tabulated for both the water well and compared to that for the average of 100 wells in the vicinity. Whenever any of these cations are excessive, in a particular well- compared to the regional average- this indicates an anomaly. Only excessive Na or Cl, & Na/Cl, compared to the regional average, will indicate sea water intrusion. Anomalous K, Ca, and Mg (in addition to boron, iron, and HCO3) will indicate other aberrations, indicating problems of a different nature. Before producing the well significantly, the original water composition can predict behavior- such as faulting, stinking, and other anomalies.
BAYS, HEADS & TOMBOLOS
Whidbey Island geography, in general, suggests that these three entities are closely related in incipience. Probably, the post-glacier sedimentary beds were connected across the land where NW-SE water passages now exist. This includes Admiralty and Saratoga Passages. As the NW-SE faulting proceeded, creating lateral fractures and later slippage along new breaks in the earth, erosion occurred faster in a NW-SE direction. This created loose sediments at openings where the sea could enter. Twice daily tides could remove these sediments, accelerating the erosion when the Sound became a body with daily movements of oscillating currents. The evidence of erosion would be removed by this moving sea water- which now creates velocities of as much as 8 knots. Of course, some of these were sand-sized particles, which were picked up by the wind to produce the dunal deposits noted in many of the cliff walls.
Admiralty Bay & Ledgewood faulting, Useless Bay & Maxwelton faulting, Saratoga Passage & Baby Island faulting, Crescent Harbor & Rocky Point faulting, and Cultus Bay-Maple Point all appear to be similar in incipience. The exception to the regional trend of NW-SE is that of Cultus Bay, which seems to be orthogonal to the usual left lateral expression. Cultus Bay is discussed under the geochemical analyses.
These sets of faults are dominantly moving laterally and cause sinusoidal expression- alternate compression and extension- in their traces along the surface, as they encounter soft or harder obstacles in their paths. The compressive cases result in Heads- such as Admiralty, Scatchet, Maylor Point, and Polnell Point.
An interesting case is that of Scatchet Head, where the NW-SE fault trace can be seen on the LIDAR map. The trace runs along lower Maxwelton Creek, and can be seen to align with the hook in Cultus Bay- which points NW. The intervening terrain has been shoved upward to cause the trace to move northeastward in the higher ground; this suggests that Scatchet Head is younger than the fault (which has probably been exerting itself for periods older than the glaciers). This is the best presented fault trace on the whole island, using LIDAR mapping. Rocky Point fault shows on LIDAR for a short distance, but disappears inland, while the Maxwelton trace crosses the whole island. Scatchet Head has been analyzed, by walking the surrounding beaches, and it has been observed that it rises to the south and falls to the east, as measured by a thick peat bed occurring in the cliffs and in the tidal zone. Scatchet head is the largest of the uplifts, and seems to be caused by compression, as is Admiralty Head, which is much smaller. A.H. can be seen to be dome- shaped, as noted by the stratigraphy, while S.H. is of such large extent, that it can only be observed as rising or falling in the elevation of the peats and the Esperance sands. In some cases, such as the Baby Island fault expression, the beds can be seen to be hardened by the compressive stresses, and this is substantiation for uplift and compression, but for S.H this is not observed. Small grabens occur on the east side of S.H., compared to uplift on the west side.
The two tombolos- Polnell and Maylor Point- represent uplifts on the southwest side of faulting, which may be compressive in nature. In the case of Maylor, the spit connection to the main island has been filled in so that the tombolo is hard to recognize; conversely, Polnell has a very tenuous connection along its spit, and has probably been washed over during some storms. It has a well-developed uplift which is contrasted with the sediments on the north side of the spit (see the LIDAR shown in the introduction). A good rule to use to recognize faulting is that every well-developed saddle in the topographical surface can be suspected as harboring a fault trace. This has worked excellently in the desert, where a topographical map can be used to find faulting by connecting the saddles with straight lines (with saddles, separating closed contours, and high ground on either side).
The sequence of events leading up to a bay development is as follows:
1. A lateral fault causes slippage and fracturing along its trace;
2. Water enters the fractures and openings and creates a creek as it flows downhill;
3. Eventually the creek is connected with the sea, and tidal wash enters the creek which is at sea level and deeper;
4. The daily oscillations of sea water remove the loosened sediment, creating a strait or canal;
5. Erosion is more rapid in the banks of these straits, and a passage is created, which may be entirely at sea level crossing the peninsula;
6. A tombolo is created on one side and a bay is created on the other side of this passage- eventually making an island of the peninsula;
7. When the island is removed by erosion, a larger bay is created. This bay is somewhat protected from the storms, and it may form spits where it connects with the larger sea. These spits may grow sea-ward, as long as the bay is protected, in contrast to the normal coastline on W.I. - which is retreating with an advancing sea.
Model based on entities observed now:
Assuming that occurrences seen on W.I. can be used through time, although they are seen only through two-dimensional space (cliffs), the following sequence is conjectured for a coastline development:
a. Meltwater flowed west from the last two lobes of ice occurring above the island (observed on LIDAR west of Freeland and Penn Cove); these two lobes, although having moved almost at right angles to each other, can be seen to have moved over W.I. from scratchings and scoopings in the sediments. Penn Cove is younger- having overprinted the older Holmes Harbor scooping, which moved almost due south and stopped at Freeland. Rocky Point, Goose Rock scratches, and LIDAR portrays the latest lobe as having moved 250 degrees from north. The Meltwater streams can be seen as subtle canyons remaining on LIDAR, and point toward the present Admiralty Passage.
b. NW-SE faulting continues (probably having been initiated in the Tertiary), and creates openings toward the NW (Seattle Pacific U. swale and Maxwelton Village swale). These were just fractures in the ground surface at first, but had preferentially faster erosion rates than surrounding areas;
c. Rebound occurs as soon as the ice melts (losing its weight, as a surface-depressing agent), and Admiralty Head, Maylor Point, Scatchet head, and Polnell Point rise- uplifting the surrounding terrain. This uplift later begins to choke off the entrances to the sea (Pacific U. swale and the lowlands at the commissary at the Oak Harbor yacht basin) which had allowed the tides to create bays along the tidal paths;
d. The bays are now large enough to have connected with the salt water proper in other directions, and they continue to enlarge with tidal wash from the west (Admiralty and Useless Bays). However, they silt up more than washes which are connected with dominant tidal paths. Further, they develop spits with the heavy load of sand which they offer;
e. The heads continue to uplift, not just by rebound, since faulting creates compression at some of them (Admiralty and Scatchet Heads);
f. This bay creation can now be seen at Cultus Bay, where the NE-SW oriented bay has now encountered the Maxwelton fault, causing the bay to make a left turn into the hook pointing to the NW-SE fault running through the Maxwelton Village (LIDAR and topographical maps). That the fault is older than the Scatchet Head can be seen by noticing that the uplift has distorted the linear fault trace- moving it to the north or NE; and
g. This compression at some parts of the lateral faulting can be seen at the low tide swale at Baby Island, where the Esperance? Sands have been hardened (Pliocene-like in strength) and pushed upward- creating a set of small hogbacks pointing up to the NE by about 20 degrees, and making a trace toward the NW for about 100-200 meters.
Dr. Harvey Kelsey has investigated this part of W.I. and determined that the Loganberry Hill swale (across Holmes Harbor from B.I.) is part of a NW-SE fault system, where a significant uplift occurred about 3200 years ago, leaving the swale on the SW side of the fault. He noticed by core sample measurements that rebound terminated about 4000 years ago or more, and that the sea has been rising since then by about 1 mm/year. The fault he investigated has caused one house in the village of Ledgewood to collapse into a slump zone at the ravine created by this same faulting. Reference: Land Level Changes from a late Holocene earthquake, GSA publication, GEOLOGY June 2004.
