carried seaward along the rill fans out as it reaches a flat portion of the beach much the same as strean-borne sediments fan out into a valley. Rill marks are apparently produced by accumulations of percolated water that seep out ofthe beach at low tide. Sand domes are small mounds in an otherwise level beach raised up by alr trapped within the sand. The air in this case is forced out as the wave swash percolates into initially dry sand. Small holes rcscm- bling those made by sandhoppers are produced when air escapcs through wet sand in the swash zonc. Other types of ripples commonly seen on beaches include oscillatory ripples, formed by the back and forth motions under waves, and current ripples, produced hy uiidirectional flow such as longshore currents, rip cur- rents, or tidal currents. The former have symmetrical crests and rounded troughs oriented parallel to the shoreline (that is, at right angles to the drection of the waves), whereas the latter are asymmetrical with gentle up-current slopes that give way to steeper slopes on the downstream side of the flow (Fig. 2.23). Current ripples are typically oriented at an angle to the shorchnc as cur- : rents tend to align themselves parallel to the coast; where rip currents lead out to sea, however, ripples tend in the F~G.2.24. Oscillatory ripple marks at 90 m depth off west coat direction of the coastline Both types of ripples arc often Vancomrr Islad, photographed from Pixa IVsubmcrsiblc, June 1977. P4pplcs 30 cm high. about 30-60 cm apart, and oriented parallel to coast. Coarse carbonate shcU hash is concentrated in troughs, and finer carbonates uxtcnd up thc flank and across crests. Small current ripples on flanh at right angles ro the horr ripples. Rattish is about 30 un long. (From Yorath et 31. 1979)

Sand ripples above the high-water mark are gena- ated by coastal winds. The orientation of these patterns depends on the prevailing wind direction so ripple crests may run at various angles to the shorelinc. Wind-gener- ated ripples are usually asymmetric with gently rising windward sidcs and stecp-sidcd leeward sides. Length scales range from a few centimctres to many metres (as for dunes). Frequently there arc ripples on low isolated mounds that are separated by relatively flat areas of sand FIG 2 23 Oscillatory ripples wrsus current ripplcs (Fig. 2.25). ,Miniature wind-shadow ridges a few cen- timetres long arc often formed in the lee of driftwood, exposed at low tide on expansive tidal flats such as the pebblcs, shells, or other objects with the ridge axis aligned Fraser River delta where, because of their large size (100 parallel to the prevailing wind direction. m or more from crest to crest and up to 1 m high), they have become known as megaripples. These sand waves are not fixed, but migrate slowly in the direction of the pre- wiling flow, both up and down current. On a recent underwater geological survey on the continental shelf off the northwest coast of Vancouvcr Island on the Ptrces N submersible, geologists further observed extensive oscillatory ripples in depths of 100 m that were oriented parallel to the coast. These ripples of carbonate shell hash and volcanic sand and pebblcs had spacings of about 100 cm and heights of over 15 cm, with rounded crests and near-flat troughs (Fig. 2.24). Calcula- tions have shown that these deep ripp caused by long, storm-generated swells southwest with heights of 10-15 m. Smaller ripples cross- ways on top of the ripples probably are produced by strong tidal currents that flow parallel to Vancouver Is- Fiti 2.26 \\'ind-induced sand rippler above higher high-warrr lcvclar land. Similar kinds ofripples have been observed at depths Cox Bay, wurh ofTofino, WcIr cobn Vanmuvcr Idand. Piccc ofmod ar to 125 m on the Oregon continental shelf. luwer ryhr is nbour 15 cm 16 in.) long il'hom hv the authnr)

- 31 . . ...C ’’ ’ >

FIG.2.26. Prominent spits in the eastern sector of Juan& Fuca Strait (A) 1. Whiffi Spit; 2. Esquimalt Lagoon (Cobourg) Spit; 3. Cordova Spit; 4. Sidney Spit; 5. Spencer Spit; 6. Spit (Marrowstone Is.); 7. Gibson Spit; 8. Dungeness Spit; 9. Ediz Hook; 10. Smith Island Spit; with expanded view of Wi Spit (B).

Frc. 2.26. Expanded view ofDungeness Spit(C),and Sidney Spit(D). Spits and Cusps 14,000 yr ago when glaciers began retreating from Juan A spit (or hook) is a beach with one end joined to the de Fuca Strait and local sea level was roughly 30 rn lower shore and the other end free where it terminates in a hook than it is today. As the ice melted and sea level rose, the or recurve (Fig. 2.26). The spit elongates in the direction Elwha River, 13 km west of Port Angeles, cut through the of longshore sediment drift and can be an alongshore glacial deposits and carried sand and gravel to the Strait. extension ofan existing beach or may be aligned across the These sediments were then transported eastward by the direction of the prevailing waves. Spits are most common prevailing littoral current set up by the action of up-strait on irregular coasts where they often grow across bay winds and waves, and the river delta grew to the east (Fig. mouths and the entrances to rivers and extend them in the 2.28a). Sea level continued to rise and additional sedi- direction of the littorsdrift. In this way, spits provide an ments were added to the alongshore drift through the effective mechanism to straighten out existing bumps in erosion of adjacent sea cliffs. This led to the creation of the coastline. Some of the more striking examples of spits small spits to the east of the delta, the forerunners of the (as well as those in Fig. 2.26) include Rose Spit and Sand present day hook (Fig. 2.28b). Growth of Ediz Hook Spit in the Queen Charlotte Islands, Ediz Hook and the began in earnest once sea level had approximately reached Smith Island Spit (Fig. 2.27) in the eastern sector of Juan its present level a few thousand years ago. With the con- de Fuca Strait, Goose Spit (PI. 5) near Comox, and Re- tinued deposition of material from the Elwha River and becca Spit on Quadra Island. Sequim Bay southeast of the erosion ofsea cliffs, the spit grew eastward as a natural Dungeness illustrates an embayment that has been almost extension of the shoreline, which itself turns abruptly totally cut off from the sea by the growth of two spits at its southeastward at the base of the spit (Fig. 2.28~).At the mouth. same time the sea cliffs were eroding southward, the Ediz Hook (Fig. 2.28) is a textbook example of how westerly base of the spit was migrating southward also. spits evolve and what effects man can inadvertently have Periodically, moreover, waves would breach the spit and on their stability. Formation of this spit started about carry sand to its inner side by “overtopping,” a process

- 32 - 33 - a deep-water port.” The suggested solution? First, build a troughs. Cusps attain maximum development during the rock revetment (retaining wall) 5 m above the low-tide transition from winter to summer beach profiles, and are level and 2 m thick on top along the northern side of the often destroyed when the transition is reversed. The rea- spit. Then nourish the seaward edge6of the spit with son for their remarkably even spacing is only now becom- sufficient beach sand (about 83,000 m3) to raisc the beach ing understood. According to the latest notions, beach profile enough to prevent initial undermining or scour of cusps are formed through the action of an alongshore the revetment toe. And finally, truck in an additional pattern of persistent nearshore circulation cells. These 10,000 m3/yr to maintain a stablc beach profile. The costs current cells are in turn generated by the interaction of for this effort runs into the millions and thcre would be no incoming surface waves with another type of wave known guarantee of success. Only time would tell if man can as an edge wave, essentially a low, visibly undetectable rectify his interference in the natural processes of beach oscillation of the sea surface with crests and troughs per- formation. pendicular to the shoreline rather than parallel as with Beach cusps are crescent-shaped shoreline features of ordinary waves. Simply put, the uniformly spaced troughs seaward protruding ridges or mounds of sand or gravel and crests of the edge wave modify the incoming breakers separated by small rounded embaymcnts. These may be along the beach in such a way that the wave swash con- isolated formations, but more commonly occur in a series verges to form cusp ridges and diverges to form cusp with fairly uniform spacing along the shore (Fig. 2.29). troughs at regular intervals. Edge waves will be included in the discussion of rip currents in Chapter 8.

Sea Cliffs to Tidal Flats Many localities along the west coast are bordered by vertical or near vertical sea cliffs that often plummet abruptly beneath the level of wave action without the hint of a backshore. Within the fiords and interconnecting channels of the sheltered inshore water are precipitous bluffs tens of metres high, where massive glaciers once gouged their way seaward through existing valleys. Ero- sion of these cliffs has generally been minimal because of the resistant nature of the rock and the low energies of the waves. In many places, large vessels can approach the cliff edge without fear of grounding. Stream valleys, which were truncated during the formation of sea cliffs, some- FIG. 2.29. Beach cusps. French Beach, near Point No Point, western times now discharge their flow via water falls from hang- Juan de Fuca Strait, February 1978. Ridges ofcoarse gravels and pebbles; adjoining troughs mostly fine gravels and sand. (For aerial view of cusps ing vallcys (Fig. 2.8). Sea cliffs in the low-resistance see Fig. 2.32.) sedimentary rocks that underly the Vancouver Island side of the Strait of Georgia and Gulf Islands are commonly Cusps arc more likely to form on coarse sand and gravcl undercut below the high-tide mark through the action of beaches than on fine sand beaches, where they tend to be waves and currents. In Active Pass, cliffs that border sporadic. They also form more readily where waves strike Galiano and Mayne islands have been undercut a metre or the shore head on and are more common in coastal ernbay- so, the process probably accelerated in recent years by ship ments than on long extensive beaches, where they tend to and ferry wakes. Wave erosion in such cases is chiefly due be obliterated by longshore currents and diagonally ap- to the hydraulic pressure exertcd during impact, which proaching breakcrs. The spacing between beach cusps is can be immense for large waves strikmg the cliff head-on. directly proportional to the height of the waves that pro- Sea cliffs on the western shore of the Strait of duced them (doubling the wave height doubles thc spac- Georgia, in the Gulf and San Juan Islands, and on the ing) and ranges from about a metrc or less on beaches outer coast are often bordered by gently sloping wave-cut with low, short waves to as much as 60 m on beaches platforms, partially exposed at low tide (Fig. 2.30). Ero- exposed to large pounding breakers. Sometimes widely sion of these particular cliffs is augmented by the abrasive spaced cusp remnants are left by storm waves on the action of sand and rock fragments thrust at the cliffs by higher levels of a beach at the same time that more closcly waves breaking over the adjacent platforms. Spectacularly spaced cusps at the lower levels are generated by smaller high sea cliffs are found in the San Juan Islands and waves. eastern Juan de Fuca Strait, e.g. Smith Island, Whidbey Ridges of the cusps generally are of coarser material Island, and the coast immediately west of Port Angeles. than the intervening troughs (Fig. 2.29) and there is Waves exploit weaknesses in sea cliffs to excavate sea usually a decrease in sediment grain size down the length caves and wave-cut galleries. (Galleries carved in sand- of the ridge. This is due primarily to the greater per- stone on Gabriola Island were used by Spanish explorers meability of the coarse material. Once the swash has de- to cache goods.) Excavations of wave-cut platforms may posited the larger sediment grains into comparatively also form tidal pools like those at Botanical Beach near steep ridges, rapid percolation diminishes the ability of Jordan hver on the Canadian side of Juan de Fuca Strait. the backrush to carry them seaward or return them to the They contain a colorful display of marine flora equal to

- 34 - become linked to the mainland by a spit or cusp-shaped deposit called a tombolo, a term that originated in Italy where such features are especially well developed. One of Canada's most famous landmarks, Perce Rock on the Atlantic coast of Quebec, is joined to the mainland by a tombolo. There are numerous tombolos on the west coast of Vancouver Island and the Olympic Peninsula as well as in the protected inside waters. Fisgard Island off Es- quimalt, Whyte Islet adjacent to Whytecliff Park, West Vancouver, and Isabella Island south of Saltspring Island are examples of tombolo-linked islands. Figure 2.32 is an excellent example of a tombolo. With the exception of the high sea cliffs, extensive sandspits, and small lagoons in the eastern end of Juan de Fuca Strait, most of the Georgia Depression is charac- FIG. 2.30. Wave-cut platform, west coast of Graham Island, Queen terized by a low coastal relief and a highly resistant Charlotte Islands. (Courtesy C. Yorath) shoreline. Shores of the comparatively low-wave environ- ment from Queen Charlotte Strait through the Strait of any in the world. Fracture zones that cut at right angles to Georgia into Puget Sound generally consist of rock)linter- ' the rocky shorelines of Juan de Fuca Strait and the outer tidal platforms up to 300 m wide, with heavily wooded coast have also allowed the surf to penetrate inland along backshores that extend down to the high-water mark. narrow steep crevices. The proliferation of these crevices, Large kelp beds frequently grow in the shallower more together with the low sea cliffs and dense nearshore plant protected areas of the platforms and great accumulations growth, make hiking the West Coast Trail both interesting of stranded logs are common along the backshore. As and challenging. Another common erosional feature stated earlier, eroded sediments are relatively scarce except along the west coast is the sea stack formed where more in the vicinity of river mouths, and thereby limit beaches resistant portions of a cliff remain standing within the surf to the pocket variety formed between resistant headlands but separated from the retreating cliff (Fig. 2.31). Exam- adjacent to unconsolidated glacial deposits and erodable ples of sea stacks are the pinnacle of rock offshore from rocks. Where streams or rivers enter marine waters, deltaic Long Beach, Duncan Rock seaward off Cape Flattery, and tidal flats of mud and sand are formed; the extent of the Siwash Rock off Stanley Park in Vancouver. A much rarer deltas is partially limited by the degree of shelter from erosional form is the sea arch, where waves have hollowed waves and currents. out a section of an otherwise resistant promontory (PI. 6). In more exposed waters, wave action modifies the Such features are quite common along the rugged Oregon backshore of the intertidal platforms more readily and coast. Under certain conditions, offshore rocks or islands bluffs are more pronounced. The western portion of Juan

----LA-- ______

FIG. 2.31. Coastal features. (See also Fig. 2.32, PI. 6.)

- 35 - F1~.2.32. TombolojoiningFrankIsl;mdmEsoarisfaPcnuurulajvstsouthofTofiooonoutcrmasrofV~au~IsLnd.Brcakingoceanwaws refnmaroundcheberkland ~d6etupalongshorecurruttrcglmethittranspornse~mcnrsmwardiceoflJland.Raultlngsp~t hasgrown seaward und itruchai island. Notice also bcach cusp$ along northern (mp) shorc oftombolo. (B.C Government Ax Photo 1969)

- 36 - m At Lon Beach, the shore is backed by logs and low vegetated if unes or cliffs. In the more quiescent areas of nearby Orice Bay, wide mud flats have evolved. With the exception of the region north and east of am Island, the coastlines ofQueen Charlotte Sound, ecate Strait, and Dixon Entrance are similar to those to the south. That is, they consist of either low shorelines adjacent -energy envir precipitous cliffs b ow wave-energy envir ments, as in fiords ecting inland channels. Beaches are mostly s ade up of pebble-cobble size material. The north and eastern shores of Graham Island, however, are a gentle, Iowland plain, less than 200 m in elevation, of well- to poorly-consolidated muds, sands, and gravels deposited by ancient streams that once flowed from glaciers that covered the Queen Charlotte Mountains. Sediment presently scoured from the adjacent FIG. 2.33. Rocky mmmdal pMom md ch& near Point No Pomt, cliffs by waves is transported withii the littoral zone uwrern Juan de Fuca Strau Vi WCSL Peck beach right of center ofphomgraph. (Photo b produced wide sandy narrower coarse gravel beaches on the ea Hydrographic charts of this de Fuca Strat, for example, is characterized by low mc!q area reveal a broad area where depths less than 50 platforms to 200 m wide with wave-cut bluffs to 20 m from Graham Island, high (Fig. 2.33). Limited amounts of sediment have ac- nearly 50 h.Swell heights in this region during a south- cumulated in small pocket beaches with large accumula- cast gale can be “mountainous” so operators of small craft tions of logs at the high-water mark. Storm waves in these are advised to check the marine forecast prior to sailing these waters. Most unconsolidated sediment withiin the nearshore zone of the coast is in deltas formed at the seaward termi- Strait are truncated by bars across their mouths and deltas nus ofstreams andrivers. Small but well-defined deltas are of limted extent. located at the heads ofinlets and certam sounds and al sections of coastal embayments. Extensive deltas exist at the mouths of larger r that dram vast areas of Pacific hinterland. The of a particular delta is de gton consist of resistant mined by the amount ofsediment transported seaward by ons of the coastal moun- the river, by the degree of sediment removal through the reach 1000 m within 10 km action of local winds, waves, and currents, and by the topography of the basin into which the river empties. River-borne sediments of silt and sand are carried down- stream as suspended load within the water or are dragged along the bottom of the main channels as traction load. Within the larger navlgable rivers of the coast, (Skeena, that face seaward are ex-

River. The downstream migration rate ofthese sand waves was as great as 75 m/day. For the larger melt-fed rivers of the coast, the annual sediment load is mostly dispersed via a deltaic distributary system during the peak runoff period from May through July. In the Fraser River, immense amounts of sediment (approximately 20,000,000 t) are trees can extend to the high- this is still small comp annually by one of the at the coast, wave em- , or the 200,000,000 Mackenzie Riw. f very low gradient tidal flats seaward edge of the delta front and the seaward limit of the salt marshes and sand

- 37