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1600-1990 mean

1600 1700 1800 1900 2000

Calendar year (A.D.) Produced by: The Cartographic Section, Dept. of Geography, U.W.0.

1600 1700 1800 1900 2000

Calendar year (A.D.) Produced by: The Cartographic Section, Dept. of Geography, U.W.0.

FIGURE 6 Comparison of the moraine record and spring temperature reconstruction between 1600 and 1990 from the southern Alaska coast. The glacial record is from Calkin et al. (in press). The temperature record is based on ring-width chronologies from three temperature-sensitive tree-line sites (Tsuga mertensiana; Wiles, 1997; Wiles et al., 1996).

compares the summary record of glacier fluctuations in the southern Kenai Mountains and Prince William Sound regions (Calkin et al., in press) with March-May temperatures reconstructed from coastal tree-ring chronologies (Wiles, 1997; Wiles et al., 1996). The reconstructed periods of lower temperatures correspond with the kill dates for trees of the forests overridden in the 1600s and early 1700s and with the dating of the LIA maximum and re-advance moraines in the nineteenth century.

For interior Alaska and the adjacent Yukon Territory, tree-ring dates are rarely available; dating control is usually provided by lichenometry and radiocarbon dating where suitable materials are present. For the Brooks Range (67°-69°N), Haworth (1988; see Calkin and Wiles, 1992) provides lichenometric data for almost 100 moraines and suggests ages clustering around ca.

AD. 1200, 1570, and 1860 (Fig. 7). The "1570" moraines are the most widely distributed and are found at 85 glaciers, though about 45 glaciers reached their maxima in the 1200s. The 1200 and 1570 events have maximum ELA depressions of 100-200 m (Calkin and Wiles, 1992). These dates indicate that LIA maximum positions were reached much earlier in this interior region than elsewhere along the PEP 1 transect. In the St. Elias-Wrangell Mountains (61°-62°N), 11 glaciers expanded during ca. 1169-959 B.P., and four moraine phases are identified based on lichenometry with dates of ca. A.D. 1500 and the late eighteenth to mid-nineteenth, late nineteenth, and early twentieth centuries (Denton and Stuiver, 1967; Denton and Karlén, 1977; Calkin, 1988). However, the physical expansion of glaciers is limited by earlier Holocene moraines in this region. A similar situation occurs in the Yukon, where mid- to late-nine-

FIGURE 7 Frequency diagram of Rhizocarpon geographicum maximum diameters from late Holocene moraines of the Brooks Range, Alaska, with approximate ages. (After Haworth, 1988; Calkin and Wiles, 1992.)

teenth-century LIA maxima were restricted by earlier Holocene deposits. In the St. Elias Range (60°-62°N), White River ash (1230 B.P.) is found in moraines of the Klutlan, Natazhat, Guerin, Giffen, and Russell Glaciers and indicates glacier advance between ca. 1250 and 100014C B.P. (Rampton, 1970, 1978). The LIAmaximum of the Kaskawulsh, Donjek, Steele, Silver, and Carne Glaciers occurred in the mid-nineteenth century (Denton and Stuiver, 1967; Sharp, 1951). Dendrochronolog-ical dating of driftwood from the beaches of neoglacial Lake Alsek, formerly dammed by the Lowell Glacier, indicate that the 595 and 623 m shorelines postdate A.D. 1848 and 1736, respectively (Clague et al., 1982; Clague and Rampton, 1982). Higher shorelines at 637 and 640 m are probably 400-500 years old (Clague and Rampton, 1982). As higher lake levels probably reflect a larger glacier dam downstream, these dates would suggest that the LIA maximum of Lowell Glacier predates A.D. 1400-1500.

In summarizing the LIA of Alaska, Calkin and Wiles (1992) comment that the LIA was the most extensive Holocene event, with advances of both land- and fjord-based glaciers in the thirteenth century (perhaps later in the interior, ca. fifteenth century). Glaciers reached their Holocene maxima between the sixteenth century and the early to middle eighteenth century. The early and middle 1700s were times of culmination of advances in southern maritime areas. Considerable glacier expansion took place in the nineteenth century, when some glaciers attained their Holocene maxima. During the twentieth century, most glaciers receded, except for those in areas of high precipitation or for some calving or surging glaciers. Present ELAs are 100-200 m higher in the interior and 300-400 m higher in maritime areas than their LIA maximum equivalents.

8.3.2. Rocky Mountains of Canada and the United States

For the continental interior sites of the Canadian Rockies (50°-52°N), there is an extensive database of dated LIA moraine sequences (e.g., Heusser, 1956; Luckman and Osborn, 1979; Smith et al., 1995) most recently reviewed by Luckman (2000a). As with the Alaskan record, the initial dating for earlier events was based on in situ or detrital overridden trees that yielded 14C ages between ca. 1100 and 450 B.P. from the fore-fields of the Kiwa, Robson, Peyto, and Stutfield Glaciers (Heusser, 1956; Luckman, 1986; Luckman et al., 1993; Osborn, 1996). Subsequent tree-ring dating of some of this material has yielded calendar dates that indicate the earliest LIA advances were between ca. A.D. 1150 and 1370 at the Robson (Luckman, 1995), Peyto (Luckman, 1996b, 2000b), and Stutfield (Robinson, 1998; see Fig. 8) Glaciers. At several sites, there has also been dating of much younger overridden and detrital material using dendroglaciological techniques (Luckman, 1996b, 1998b; Robinson, 1998; see Fig. 8). In most cases, this material is associated with a single late-eighteenth-century and early-nineteenth-century glacier advance that culminated in the mid-nineteenth century. However, there is evidence at two sites (Manitoba and Saskatchewan Glaciers; Fig. 8; Robinson, 1998) that trees were also overridden by an earlier advance in the late seventeenth century.

The surface glacial record is based on lichenometric and tree-ring dating of moraines at over 65 glaciers (Luckman, 1996b, 2000a; Fig. 8). Scattered evidence is available for glacier fluctuations between ca. A.D. 1400 and 1600; some moraines are dated to this period by lichenometry or dendrochronology, but the morphological evidence is fragmentary and most are considered limiting dates. Two major subsequent moraine-building periods are identified in the early eighteenth century and the mid to late nineteenth century. The maximum regional extent of ice probably occurred in the first half of the nineteenth century, although at many glaciers extents were slightly greater in the eighteenth century; there are regional differences in this pattern within the Canadian Rockies (Luckman, 2000a). At many sites, glaciers re-advanced several times in the late nineteenth century to positions close to the LIA maximum moraines. During the twentieth century, the dominant pattern has been one of glacier recession with a minor re-advance during the 1960-80 period at several sites (Luckman et al., 1987).

Figure 9 shows a recent spring-summer (April-August) temperature reconstruction based on tree-ring densitometry from Picea engelmannii and Abies lasio-carpa at the Columbia Icefield (Luckman et al., 1997).

FIGURE 8 Dates of periods of glacier advance and moraine formation in the Canadian Rockies (Luckman, 2000a). Horizontal lines represent calendar-dated records of the minimum life span of glacier overridden or killed trees in six glacier forefields. Outer ring dates from logs at Manitoba and Saskatchewan Glaciers suggest that these assemblages may contain trees killed during more than one glacier advance. The moraine data are based on lichenometric and tree-ring dating in 66 glacier forefields (see Luckman, 1996a, 2000a).

FIGURE 8 Dates of periods of glacier advance and moraine formation in the Canadian Rockies (Luckman, 2000a). Horizontal lines represent calendar-dated records of the minimum life span of glacier overridden or killed trees in six glacier forefields. Outer ring dates from logs at Manitoba and Saskatchewan Glaciers suggest that these assemblages may contain trees killed during more than one glacier advance. The moraine data are based on lichenometric and tree-ring dating in 66 glacier forefields (see Luckman, 1996a, 2000a).

This record shows a strong agreement between periods of glacier advance/moraine building and periods of lower summer temperatures in the 1200s through 1300s, late 1600s through early 1700s, and throughout the nineteenth century. This agreement suggests that summer temperatures are a primary control of glacier fluctuations in this region. Recently, Watson (1998; Luckman and Watson, 1999) has provided the first precipitation reconstruction for this region of the Canadian Rockies. Examination of this record (Fig. 9) shows little obvious correlation with the glacier record, except possibly for the late 1600s and the mid-twentieth-century advance. However, the changes in mass balance at Peyto Glacier since 1976 (Luckman, 1998b; Demuth and Keller, 2000) indicate that increasingly negative mass balances reflect decreasing winter accumulation rather than summer temperature influences.

LIA moraines (late neoglacial or Gannett Peak equivalents) have been extensively reported for sites in the American cordillera (see Davis, 1988), but have rarely been precisely dated. The most commonly utilized dating technique has been lichenometry. In the

Colorado Rockies (ca. 40°N), lichenometric dating suggests the oldest LIA moraines date from the late seventeenth century through the early eighteenth century (Benedict, 1973), similar to those in the Canadian Rockies. For intervening sites in Glacier National Park, Montana (49°N), Carrara and McGimsey (1981) report tree-ring-determined LIA maximum dates of ca. 1860 for two of the larger glaciers. Most other glaciers have single late Holocene (LIA) moraines that are assumed to date from the mid-nineteenth century (Carrara, 1987). Over half of the more than 150 small glaciers that were present in Glacier National Park in the 1850s have subsequently completely disappeared (Carrara, 1987).

8.3.3. Coast Ranges of British Columbia and the Pacific Northwest of the United States

Glacier fluctuations in the Coast Ranges of western British Columbia show a broadly similar pattern to that in the Canadian Rockies. There is a growing body of data from subtill radiocarbon ages and lacustrine

FIGURE 9 Regional glacier, proxy temperature, and precipitation records for the Canadian Rockies. The regional moraine record is from Luckman (2000a). Temperature reconstruction is from Luckman et al. (1997) using ring-width and densitometric data for Picea engelmannii and Abies lasiocarpa. Precipitation reconstruction is from Watson (1998) using ring-width data for Pseudotsuga menziesii at the Powerhouse site near Banff. Both tree-ring records are smoothed with a 25-year filter.

FIGURE 9 Regional glacier, proxy temperature, and precipitation records for the Canadian Rockies. The regional moraine record is from Luckman (2000a). Temperature reconstruction is from Luckman et al. (1997) using ring-width and densitometric data for Picea engelmannii and Abies lasiocarpa. Precipitation reconstruction is from Watson (1998) using ring-width data for Pseudotsuga menziesii at the Powerhouse site near Banff. Both tree-ring records are smoothed with a 25-year filter.

episodes that indicates initial LIA advances between 900 and 400 14C B.P. Ryder and Thomson (1986) report subtill maximum ages of ca. 900 ± 40 14C years B.P. at Klinaklini Glacier, 835 ± 40 at Franklin Glacier, 680 ± 50 and 540 ± 45 at Bridge Glacier, and 460 ± 40 at Sphinx Glacier in the southern Coast Mountains (49°-51°N). Ryder (1987) provides subtill 14C ages of 455 ± 65 and 625 ± 140 at Scud Glacier, 595 ± 60 at Glacier B in the Stikine area (56°-57°N), and 400 ± 60 for the Ja-cobsen Glacier in the Bella Coola area (52°N; Desloges and Ryder, 1990). The range of these 14C ages indicates the possibility that there may have been several periods of glacier advance between the twelfth and sixteenth centuries, but this can be demonstrated only in the Bella Coola area. Desloges and Ryder (1990) report on a section from the lateral moraine of Purgatory Glacier indicating that the glacier advanced over an older till at ca. 785 14C B.P. (ca. A.D. 1220), re-advanced after 630 14C B.P. (A.D. 1410), and remained extensive until after A.D. 1840. At several localities, LIA glacier advances impounded glacial lakes. Recently obtained sections in the deposits of Ape Lake (52°N; Desloges and Ryder, 1990) indicate that the glacier impounded the lake 100-200 years before 770 14C B.P. Farther north, the deposits of Tide Lake (ca. 56°N), impounded between the Frank Mackie and Berendon Glaciers, indicate several neoglacial lake phases, the last major impoundment beginning at ca. 1000 14C B.P. and finally draining at ca. A.D. 1920-30 (Clague and Mathewes, 1992).

Dating of LIA moraines is based largely on mini mum limiting ages for moraines determined by dendrochronology and limited historical observations (e.g., Ryder, 1987). At Tiedemann Glacier (51°N; Ryder and Thomson, 1986) and Berendon Glacier (56°N; Clague and Mathewes, 1996) older neoglacial moraines are locally preserved, dating from ca. 2800-2200 14C B.P. Figure 10 shows moraine histograms for the southern Coast Ranges (49°-51°N; Ryder and Thomson, 1986) and the Bella Coola region (52°N; Desloges and Ryder, 1990) with comparative data for coastal Alaska (59°-60°N) and the Canadian Rockies (50°-52°N). In the southern Coast Ranges, a small number of glaciers had maxima in the early 1700s, but most had maxima in the nineteenth century with the majority between 1850 and 1900 (Ryder and Thomson, 1986). In the Bella Coola area farther north (Desloges and Ryder, 1990), all the tree-ring-dated moraines were built after 1825, and 12 of the 16 moraines were formed between 1850 and 1900. In discussing results for the Bella Coola area, Desloges and Ryder (1990) suggest that the LIA began slightly later and may have terminated slightly later in the British Columbia Coast Ranges compared with the Rockies. They suggest that the mass balance of these coastal glaciers is strongly controlled by precipitation and is linked to changes in the midlatitude circulation pattern in the adjacent Pacific. However, reconnaissance observations by Smith (personal communication, 1998) do indicate the presence of seventeenth-century moraines in the Bella Coola area, and Clague and Math-ewes (1996) report that the LIA maximum of Berendon Glacier, farther north (56°N), predates 1660. For the Stikine area (57°N), Ryder (1987) estimates the LIA maximum moraines of the Great, Mud, and Flood Glaciers to date from the late seventeenth century to the early eighteenth century, but most other glaciers examined in this area reached their maxima in the mid- to late nineteenth century.

Although many small glaciers occur on Vancouver Island, the only dating presently available comes from the Moving Glacier (49°30' N; Smith and Larocque, 1996). Cross dating of a subtill detrital and in situ assemblage of logs from a gully section, 200-300 m up-ice of the LIA terminal moraine, revealed outermost ring dates of 1713 from the gully and 1718 for an adjacent site, 30 m downvalley. A log protruding from the terminal moraine had an outermost sound ring of A.D. 1818 (the outermost rings were rotted), providing a minimum age for the LIA maximum of this glacier. These data indicate that the glacier was advancing close to the LIA maximum position in 1718 and receded from that limit sometime after 1818 (i.e., as with the adjacent Coast Mountains, the glacial maximum was in the nineteenth century). Aerial photographic evidence indicates that the glacier occupied 77% of its LIA maximum area in 1931 and 20% in 1981.

Results for British Columbia suggest that, with mi

S. Kenai Mtns., Alaska Bella Coola Region, B.C. Coast Ranges, B.C. Canadian Rockies

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