of a hurricane hit Caroline, rearranging tons of coral rubble and 

 sand on the windward beaches and motus, tearing out 

 Tournefortia scrub, obliterating much of the native herb mat, 

 exposing beachrock, depositing large chunks of broken reef on 

 the seaward reef flats, and changing the sizes and shapes of the 

 beach crests. 



Reef Rim w ith Motu : The w idth of the seaward flats is 

 quite uniform, averaging 307 m (range 1 93-396 m), occupying 

 517c of the rim width. It consists of a slightly raised algal ridge 

 bearing the brunt of incessant wave action and a rubbly reef flat, 

 partly drying at low water, which sweeps up to the motu's 

 beach (PI. 16). Adjacent to Nake, in the northeast, the seaward 

 margin forms a shallow moat separating the land and algal 

 ridge (PI. 13). 



The motus differ considerably in width, ranging from the 

 narrow tip of Long, merely 30 m wide, to Windward, 290 m 

 wide. Nake and South islands, forming "caps" to the atoll at its 

 upper and lower ends, respectively, exhibit characteristics 

 more typical of windward than leeward motus. Because coral 

 debris accumulates wherever atoll reefs turn sharply (Thomas. 

 1961), these two motus are the widest on the atoll (Pis. 16.17). 

 A comparison of maps a century apart ( Figs. 2.4) indicates that 

 several layered ridges of coral debris have accumulated on 

 northern Nake since 1883. 



Reel Rim without Motu : Zonation within the reef flat is 

 less marked where there is no land. Within these interislet reef 

 flats, however, certain areas of high water transport have 

 carved surge channels and grooves. These are particularly 

 e\ ident at the north and south ends of islets ( PI. 18), between 

 islets, and within the longer flats. In all these areas, tidal tans 

 extend into the lagoon especially at its northern end where 

 sedimentation is most active. Caroline has no deep pass or 

 navigable channels into the lagoon nor a ship anchorage 

 beyond the reef, though small boats may anchor within the 

 close lee of South Island during normal trade winds and low 

 seas. Landing in an inflatable is best made across the reef 

 slightly north of the "boat entrance" (marked by an upright 

 anchor I. 



The reef flat between Tridacna and South Island, serrated 

 with 6 erosional grooves, one labelled "blind passage." is of 

 particular importance to navigators. Its most southerly channel 

 is a narrow diverticulum 380 in long within a reef 430 m wide. 

 On all previously published maps this passage is drawn as 

 though it completely connects ocean and lagoon (Figs. 4-7). 

 However, it is a true blind channel (Fig. 50), serving as a 

 sheltered anchorage for motored yachts near its lagoon end. hut 

 cannot be entered or exited during high winds or moderate-to- 

 high surf. 



Leeward Reef Flats : These are wider, flatter, gentler, more 

 consolidated, and less filled with rubble than the windward 

 reefs(Pl. 1 1 ). Everywhere except within the surge channels, an 

 orange-colored alga blankets the coralheads. chunks of upraised 

 coral (PI. 11). carbonate rock, and giant clams. This alga is 

 found on many atolls — for example Enewetak and Rangiroa 

 (Stoddart & Sachet. 1969: US Department of Energy. 1987). 

 Living coral is sparse. 



Surge Channels : These occur in a variety of shapes and 

 sizes, depending on the distances between motus, the extent 

 and buildup of reef flats adjacent to land, and lagoon depth. 

 Surge channels and reef grooves (hoa) are deeper on the 

 windward side. Aerial photos indicate that the vigorous 

 currents washing daily into Caroline's lagoon have created 

 largerdebris fans between windward motus than between those 

 to leeward (see Chapter Frontispiece). 



Beaches 



Caroline's beaches — the zones lying between low water 

 mark and the inland limit of wave-deposited debris — are entirely 

 of reef origin. There is, however, considerable variation in the 

 sizes of coral rubble, and the proportions of sand and silt with 

 which they are mingled. In general, the windward beaches and 

 surge channels, subject to winds and swells and in a constant 

 state of erosion or deposition, support the greatest variety of 

 sediments: well-sorted sands; gravels of coralline, algal, and 

 molluscan origin; and a wide variety of sizes of coral rubble. 



Almost all exposed rubble on Caroline is colored from 

 pale to dark gray , aconsequence of penetration by cyanobacteria 

 (Fosberg, 1953). Typically the oldest rubbles, highest up the 

 beach and extending into the interior, are darkest. A marked 

 beach crest rises — gently or abruptly — from the windward 

 beaches, at the crest of which is deposited an assortment of 

 flotsam and jetsam: bottles, plastic, wood, coconuts, et cetera 

 (Pis. 16,20). No large chunks ofdisengaged reef were found on 

 or near land in 1988. but in 1990 many of these littered the 

 windward reefs and shores, the result of cyclonic weather in 

 February of that year. Similarly, in 1990, considerably thicker 

 deposits of coarse sand had overlain the rubbly windward 

 beaches and interislet channels of 1988. 



Alterations to Caroline's beaches provide the major areas 

 of change in islet shape. The main areas of aggradation are on 

 the northwest and southwest leeward points of the 

 windward islets. This is particularly true of the largerones such 

 as Brothers (which has joined with a separate islet 

 mapped by Arundel ). and Windw ard and Tridacna ( which have 

 added more sediment to their southwest points during the last 

 century). 



Beachrock : These narrow, elongated strata of eroded 

 upraised reef, brown consolidated sands, and reef detritus are 

 not abundant on Caroline. Occurring as strips at the low water 

 mark, they flank the windward beaches of Nake, Long, and 

 South (Figs. 37.38.50; PI. 58) and a few of the leeward islets. 

 They become more exposed alter violent storms. Extensive 

 areas of a coarser conglomerate (PI. 21 ) hug the inner reef flats 

 of western South Island. 



Upraised Reef : In a lew areas, jagged, eroded upraised 

 reef {champignon or /<•<<) is evident — for example, the lower 

 quarter of Long. A thin soil cover supports a forest of lower 

 stature than would otherwise be expected. In this minikarst 

 area the rocky substrate is pitted with holes of varying sizes and 

 undermined with subterranean tunnels in which at least two 

 species of land crabs (Birgus latro, Cardisoma spp. ) shelter 

 ( PI. 22). Noddv Rock (PI. 1 9). the smallest motu (0.02 ha), and 



11 



