A Geologic Guide to Wrangell–Saint Elias National Park and Preserve, Alaska A Tectonic Collage of Northbound Terranes By Gary R. Winkler1 With contributions by Edward M. MacKevett, Jr.,2 George Plafker,3 Donald H. Richter,4 Danny S. Rosenkrans,5 and Henry R. Schmoll1 Introduction region—his explorations of Malaspina Glacier and Mt. St. Elias—characterized the vast mountains and glaciers whose realms he invaded with a sense of astonishment. His descrip­ Wrangell–Saint Elias National Park and Preserve (fig. tions are filled with superlatives. In the ensuing 100+ years, 6), the largest unit in the U.S. National Park System, earth scientists have learned much more about the geologic encompasses nearly 13.2 million acres of geological won­ evolution of the parklands, but the possibility of astonishment derments. Furthermore, its geologic makeup is shared with still is with us as we unravel the results of continuing tectonic contiguous Tetlin National Wildlife Refuge in Alaska, Kluane processes along the south-central Alaska continental margin. National Park and Game Sanctuary in the Yukon Territory, the Russell’s superlatives are justified: Wrangell–Saint Elias Alsek-Tatshenshini Provincial Park in British Columbia, the is, indeed, an awesome collage of geologic terranes. Most Cordova district of Chugach National Forest and the Yakutat wonderful has been the continuing discovery that the disparate district of Tongass National Forest, and Glacier Bay National terranes are, like us, invaders of a sort with unique trajectories Park and Preserve at the north end of Alaska’s panhan­ and timelines marking their northward journeys to arrive in dle—shared landscapes of awesome dimensions and classic today’s parklands. geologic features. In 1978, the United Nations recognized This geologic guide includes six parts: the first part the global importance of Wrangell–Saint Elias and Kluane by briefly notes the 150-year history of exploration in the designating them as “World Heritage” sites; Glacier Bay and Wrangell–Saint Elias region that preceded the 20th century Alsek-Tatshenshini were similarly designated in 1992, unify­ and summarizes the ensuing 100-year history of earth-science ing some 24 million acres of international parklands. The investigations that have brought us to our present understand­ array of geologic features makes these parklands an impressive ing of the geologic makeup of the parklands. outdoor laboratory. Within Wrangell–Saint Elias are displayed The second part describes that geologic makeup, inter­ features that indicate (1) how the southern Alaskan continental preting features of the Wrangell–Saint Elias region in the margin has more than doubled in size in approximately the context of plate tectonics and accretionary terranes. (It was past 200 million years by incremental addition of far-traveled earth-science studies in this part of south-central Alaska, after geologic fragments; (2) how underthrusting by the Pacific all, that sparked development of, or provided early tests for, oceanic plate6 has prompted rapid uplift, voluminous vol­ some fundamental tectonic and terrane concepts.) This second canism, and powerful earthquakes; and (3) how uplift of the part sets the Wrangell–Saint Elias region within a present coastal mountains adjacent to the storm-brewery of the Gulf framework of a tectonically active continental margin strad­ of Alaska has engendered large and scenic systems of alpine, dling part of the boundary between major crustal plates—the piedmont, and tidewater glaciers. North American continental and Pacific oceanic plates. It In 1892, glaciologist Israel C. Russell, writing of one is the contemporary convergence between these plates that of the earliest scientific probes of the Wrangell–Saint Elias engenders some of the park’s most notable features—its vol­ canoes, lofty coastal mountains, and network of major crustal breaks along which occur frequent damaging earthquakes. 1U.S. Geological Survey, Denver, CO 80225-0046. This present is also key to the parkland’s past, for 21104 Partridge Drive, Carson City, NV 89701. geologic terranes have been converging on—and accreting 3U.S. Geological Survey, Menlo Park, CA 94025. to—Alaska’s continental margin for much of the past 200 4U.S. Geological Survey, Anchorage, AK 99508-4667. million years. The sequential accretion of these terranes has 5National Park Service, Copper Center, AK 99573. accumulated a vast collage in the Wrangell–Saint Elias region, 6Terms in italics are defined in a glossary that begins on page 150. and the third part of the guide characterizes each geologic ter­ rane in the collage—proceeding from north to south, the same sequence by which the terranes were accreted to the Alaska Lull (1989). A report by Richter and others (1990) provides continental mass. the most complete discussion of volcanism in the Wrangell The fourth part recapitulates the geologic dynamism of Mountains, but numerous additional reports by Richter and the parklands, describing how earthquakes, volcanoes, and his colleagues also could be referenced here, including an glaciers continuously reshape the landscapes of the park. important guide to the principal volcanoes in the parklands A stampede of gold-seekers toward the rich placer (Richter, Rosenkrans, and Steigerwald, 1995). MacKevett and diggings of the Klondike first brought prospectors to the others (1997) provided the definitive summary of the remark- Wrangell–Saint Elias region. However, it was discovery of ably high grade copper deposits of the Kennecott-type, the fabulously rich copper deposits in the McCarthy area that led presence of which provoked, directly or indirectly, many of the to the major industrial developments along the southern flank earth-science studies that have brought us to today’s state of of the Wrangell Mountains in the early 20th century, includ­ geological understanding of the Wrangell–Saint Elias region. ing construction of a major railway and creation of a major A categorized list of sources of information for this integrated mining company. The fifth part of this guidebook guidebook, including those just cited, and suggested additional characterizes the copper and gold resources of the parklands, reading, including geologic and topographic maps, is included including the exceptionally large and rich deposits of the beginning on page 158. The list is not intended to be compre­ Kennecott-type. It was development of these resources that hensive, but many of the included references contain extensive created the infrastructure still in use in today’s parklands. bibliographies that can be used to guide more detailed investi­ The sixth part is a series of geological sketches of out- gations of topics that are touched upon herein. An index map standing places within Wrangell–Saint Elias National Park and showing the localities of photographs used in this guidebook Preserve. It includes descriptions of locales where some of also is included near the end (fig. 78). the plate tectonic processes of part two are exemplified best or In preparing this geologic guide, the authors and con­ where particular features of the geologic terranes of part three tributors acknowledge the invaluable work of Fred H. Moffit, are most clearly displayed. whose geologic studies in Alaska—and particularly south- Some previous exposure to geological ideas will be help­ central Alaska—spanned nearly five decades. His sustained ful, because many technical terms are used in what follows. efforts in the Wrangell–Saint Elias region provided a broad However, a glossary of geologic terms is included near the end foundation for all who followed. of this guidebook that briefly defines what may be unfamiliar terms. A term that is defined in the glossary is italicized the first place where it appears in the text or in a figure caption. Exploration Many place names and geographic terms also are used. Thus, a topographic map of Wrangell–Saint Elias National On July 16, 1741, after an arduous voyage from the Park and Preserve and a dictionary of Alaska place names will Russian Far East, Vitus Bering finally glimpsed the moun­ be valuable companions to this guidebook. tainous mainland of southern Alaska, a prominent ice-clad Citations have not been inserted in the text to indicate summit many leagues distant rising above thick stormy banks sources for geologic data and interpretations. However, the of clouds. Desperate to secure fresh water and whatever following principal sources could have been cited repeatedly, resources land might offer, the navigator sailed in its direction, for they are original, authoritative, and thorough. Published passing a conspicuous cape at the southwest end of Kayak geologic maps of the Nabesna quadrangle (Richter, 1976) and Island on July 20, and making a hurried landfall nearby. In the McCarthy quadrangle (MacKevett, 1978) and unpublished honor of the patron saint of the day, the island was named geologic mapping of the Bering Glacier, Icy Bay, Mt. St. Elias, Saint Elias, the name subsequently applied to the headland and and Yakutat quadrangles by George Plafker depict the funda­ the towering mountain also. Georg Steller, a naturalist on the mental geologic setting of terranes in the parklands and are expedition, was included in this first Alaskan landing party, accompanied by text that describes the rock units, interprets spending a tantalizing few hours ashore collecting floral and their genesis, and summarizes the tectonic evolution of large faunal specimens, briefly examining evidence of native inhab­ regions of