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Lake Clark

National Park and Preserve


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park geology subheading
photo of mountains at Lake Clark
Lake Clark National Park and Preserve, Alaska

In geologic time, the region is not particularly old. Excluding a few greenstone deposits (395-440 million years old), rock outcrops formed between the earth.s beginning (4.6 billion years ago) and 225 million years ago (end of the Paleozoic Era) are absent. This is because LACL is the scene of a dynamic, living geology. A young landscape shaped by uplift, intrusion, earthquakes, volcanism, and glaciation. The Aleutian Range in LACL is a segment of the circum-pacific Ring of Fire, one of the most active volcanic belts in the world. Quaternary volcanism in the Aleutians is the result of plate convergence, approximately 7.0 cm/year, between the American and Pacific plates (Figure 4) (Kienle and Swanson, 1983). Modern tectonism is evident from the frequent strong earthquakes and four active volcanoes in the region (Redoubt, Illiamna, Augustine, and Douglas). Clusters of shallow and deep seismicity, with some magnitudes exceeding 6.0 on the Richter scale, have been recorded beneath Iliamna, Augustine, and Douglas volcanoes (Hampton, 1982). The most recent series of eruptions in the park was by Redoubt Volcano in 1989-90.

Most of the southern portion of LACL, east of Lake Clark, consists of sedimentary andmetamorphic rock of Mesozoic age. The geology in the northern half of the park is dominated by Tertiary and Mesozoic intrusive rocks (Dale and Stottlemyer, 1986). In detail, the geology and associated structure are very complex with igneous, metamorphic and sedimentary lithologies interacting at various scales. Two major thrust faults are located within LACL (Figure 5). The Bruin Bay Fault can be traced 300 miles from Becharof Lake on the Alaska Peninsula to Mount Susitna, northwest of Anchorage, bisecting Chinitna and Tuxedni bays. The Lake Clark Fault, also referenced as the Castle Mountain Fault by Stone (1983) in Figure 4, runs approximately 80 miles to the northeast end of Lake Clark (Alaska Geographic Society, 1986).

The Lake Clark Fault underlies Lake Clark, structurally producing the lake.s long linear geometric shape. The fault is characterized by a right lateral displacement of approximately 8 miles (Ivanhoe, 1962).


Currently, there have been no comprehensive soil surveys conducted in LACL (Natural Resources Conservation Service, 1998). In fact, minimal soil survey work has been conducted in Alaska. In general, soils in LACL are young, poorly developed, extremely variable and derived from glacial or volcanic processes (Racine and Young, 1978). The land surface below 1500-2000 ft. (msl) elevation has been scoured by Pleistocene glaciation. The topography above approximately 2000 ft. (msl) is either too steep to retain soils, covered by snow and ice, or at too great an elevation for soil-forming vegetation to grow. Soils west of the northern-most lakes (Twin Lakes, Turquoise Lake and Telaquana Lake) are better developed and support suitable rangeland for a healthy caribou herd (Chamberlain, 1989).


LACL.s geographical setting and mountainous topography have resulted in several distinct physiographic regions. Racine and Young (1978) identified the following five physiographic regions within LACL.s boundary: Coastal region, Montane region (Aleutian Range, Alaska Range), Lake Clark-Kontrashibuna region, Foothill Lakes region, and Interior Lowlands region (Figure 3). The Coastal region is located in the southeastern part of the park and borders Cook Inlet. This region includes the lowlands between Cook Inlet and the upper elevations of the Aleutian Range (4000 - 5000 ft. msl). Large tidal fluctuations and glacial outwash along the coast have resulted in well-developed estuarine salt marshes. The Montane region includes the upper elevations of the Alaska and Aleutian ranges and represents a vast upland of alpine tundra, glaciers, permanent snow, ice and rock. Immediately west of the Montane region and penetrating these mountains in places along their west side are the Lake Clark-Kontrashibuna and Foothill Lakes regions. These regions are more closely related to interior and western Alaska than to the Coastal region to the east. The Lake Clark-Kontrashibuna region includes the Lake Clark watershed and constitutes low elevation valleys and mountain slopes bordering the several lakes. The Foothill Lakesregion occupies the high plains and plateaus of moraines just west of the mountains. The area is characterized by a series of large glacial lakes fed by meltwater from the Montane region. From south to north the main lakes are: Twin Lakes (1979 ft msl), Turquoise Lake (2504 ft msl), Lake Telaquana (1219 ft msl), and Two Lakes (1132 ft msl). The Interior Lowlands region occupies a small relatively flat area in the northwest corner of LACL. Drainages here include the Telaquana River and the Stony River, which flow west into the Kuskokwim River. Elevations of these broad flat valleys are low (around 1050 ft msl), and the climate is more typical of interior Alaska than the other four physiographic regions in LACL.


The Alaska and Aleutian mountain ranges form a continuous watershed divide separating the coast from the interior. LACL.s most dominant interior drainage basin is the 3000 mi2 Lake Clark drainage, which feeds Little Lake Clark, Lake Clark and Six Mile Lake (Brabets, pers. comm., 2000). The Lake Clark drainage is part of the Kvichak River Basin (see Figure 6), which drains Lake Clark (143 mi2) and Lake Iliamna, the largest lake in Alaska (1226 mi2). The 60-mile-wide basin extends northeastward from the northeast tip of Bristol Bay (Kvichak Bay) approximately 170 miles into the northwest slopes of the Aleutian Range. This basin also drains part of Katmai National Park and Preserve (Alagnak Wild River). The Kuskokwim River Basin drains the Stony, Necons, and Telaquana rivers, located in the northern portion of Lake Clark National Preserve, into Kuskokwin Bay. This large basin is approximately 500 miles long and averages 100 miles in width. The Nushagak River Basin drains the Mulchatna and Chilikadrotna rivers, located along the western portion of LACL, into Bristol Bay and is approximately 220 miles long and 100 miles wide. Along LACL.s eastern boundary is the coastal drainage basin, which includes the Chakachatna River Basin. Streams along the coast drain the eastern mountain slopes to Cook Inlet (U.S. Department of the Interior, 1952). These coastal drainage basins include the following park drainages: Chilligan River, Igitna River, Neacola River, Drift River, Crescent River, Tuxedni River, Johnson River, and West Glacier Creek. The major drainage basins within LACL.s boundary are presented in Figure 6.

Glaciers, Lake Ice, and Snowpack

As evident in Figure 7, the hydrologic cycle in the park is influenced in part by extensive glaciers and snowfields that supply vast quantities of silty meltwater to the headwaters of drainage basins during the summer months. Glacial ice, much of it associated with Redoubt and Iliamna volcanoes, covers approximately 30% of the park. Most of the glaciers in the park have retreated dramatically in the last four decades, which indicates that melting is occurring faster than snow accumulation (National Park Service, 1999a). Seasonal ice and snow cover affects the characteristics of aquatic ecosystems. They control the amount of light reaching the unfrozen water beneath the ice (Prowse and Stephenson, 1986). Ice can also prevent gas exchange between underlying waters and the atmosphere and may commonly lead to depletion of dissolved oxygen and the build up of reduced gasses such as CO2, CH4 and H2S (Rouse et al., 1997). The processes accompanying ice formation during freeze-up and break-up have a wide range of effects on the bed, banks, and biota of lakes and rivers. These include frazil ice (aggregate of ice crystals formed in supercooled turbulent water) impact on fish and invertebrates, anchor ice growth, elevated water levels, channel blockage and increased scouring (Prowse, 1994.) The snow line in LACL begins between 4000 . 5000 ft msl on the east side of the mountain ranges and approximately 8000 ft msl on the west side (Karlstrom, 1964). The overall absence of advanced forest at the higher elevations allows for little mitigation of runoff waters. Water quality from melt water in LACL is likely influenced by the bedrock (Dale and Stottlemyer, 1986).

Although permafrost is not prevalent in LACL, it is distributed sporadically at considerable depth in isolated areas of predominately fine soils where insulation is high (Chamberlain, 1989). Permafrost can influence the hydrologic cycle. For example, permafrost can impede precipitation from recharging aquifer systems. This could result in a greater surface runoff contribution to lake and stream recharge.

Coastal Environments

LACL.s marine shoreline extends north from Chinitna Bay approximately 125 miles to Redoubt Point. According to an inventory of the physical and biological resources of LACL.s coastline prepared by Bennett (1996), LACL.s coastal environments are among the most important and biologically productive ecosystems in the Gulf of Alaska. The trophic relationship between shorebirds, seabirds, ducks and intertidal infauna may represent the most significant predator-prey relationships along the park.s coastline (National Park Service, 1999a). Table 3 provides an inventory summary of the park.s coastal environments. Salt marsh and mud flats make up most of LACL.s coastline (22% of the total length each; and 42% and 24% of the total area, respectively). The management of lands along the LACL coastline can be complex since large blocks of land were conveyed to native corporations or are still being adjudicated under the Lands Act (Bennett, 1996).

Volcanic Environments

There are two active volcanoes within the boundaries of LACL; Redoubt and Iliamna. Extensive physical changes in riparian and aquatic habitats have resulted from volcanic induced disturbances in the Cook Inlet region. Along with ash deposition, eruptions in the region have caused massive inputs of water and sediment into stream channels emanating from glaciers and snowfields on the volcanoes (Dorava and Milner, 1999). Redoubt Volcano is drained on the north by the Drift River, on the east by Redoubt Creek, and on the south by the Crescent River, all of which flow into Cook Inlet. The volcano has produced at least 30 large tephra-forming eruptions during the past 10,000 years. Eruptions in 1902, 1966, 1968, and 1989-90 produced ash and generated floods in the Drift River by melting part of the volcano.s extensive glacial cover (Till et al., 1992).

The 1989-90 volcanic eruptions altered the hydrologic and geomorphic conditions of a 126-mi2 area north and east of the volcano. Volcanic activities that affected the watershed include an ice and rock avalanche, pyroclastic surge and flow, and lahars (mudflows composed chiefly of volcaniclastic materials). The eruptions melted and eroded snow and glacial ice, destroyed riparian vegetation, filled the valley bottom with sediment, and altered stream channel geometry (Dorava et al., 1993) In 1990, a study of Lake Clark (Stottlemyer, 1990) was conducted to repeat the basic limnological measurements recorded during a 1985-87 multiple lake study (Chamberlain, 1989) to determine how physical properties of Lake Clark and surrounding lakes may have been altered by ash inputs from the 1989-90 Redoubt eruption. According to Stottlemyer (1990), turbidity was considerably higher throughout Lake Clark after the eruption, decreasing light penetration and reducing the lake volume in which phytoplankton can photosynthesize by more than 70%. Some impacts from volcanic eruptions are short-term (< 5 years), while others last much longer. In comparing macroinvertebrate community composition in the Drift River, after the 1989-90 Redoubt eruption with nearby undisturbed streams, Dorava and Milner (1999) found the Drift River macroinvertebrate communities still recovering after 5 years.

Minerals Extraction

Under the Alaska Native Claims Settlement Act of 1976 (ANCSA), the Cook Inlet Region Corporation (CIRI) received title to approximately 21,000 acres of land known as the .Johnson River Tract. located on the west side of Cook Inlet in LACL. The Johnson River Tract is divided into two tracts. The northern tract is 9,600 acres of mineral estate; the southern tract is 11,342 acres of surface and subsurface estate. An ancillary camp and airstrip were constructed at the headwaters of the Johnson River in 1983. Since then, mineral exploration has been continuous. A high-grade deposit of copper, silver, lead, zinc, and gold has been delineated from a 1993 exploratory drilling program in the area. CIRI is investigating possible partnerships to extract the deposits, which includes exploratory engineering and economic feasibility of access routes from the deposits to Cook Inlet [Cook Inlet Region, Inc. and Westmin Resources Limited (1994), National Park Service (1999a)]. The Johnson River headwaters have the potential to become the largest commercial mining operation within an Alaskan park. Based on the current size estimate of the ore body, approximately 270,000 tons of ore would be mined and transported annually over a 3-year mine life (National Park Service, 1999a). Due to the proximity of the planned mine and support network of roads and ore stockpiles to the Johnson River, there is a high potential for contaminants to reach the Johnson River estuary and be transported along the coastline by prevailing tidal currents (Bennett, 1996). CIRI maintains that conveyances and transportation easements granted under ANCSA are exempt from the requirements of NEPA, and a formal decision is pending. CIRI and Westmin Resources Ltd. prepared an environmental assessment in 1993, but it only addressed the selection of a transportation corridor across NPS land and a port site as granted by ANCSA. Fuel would be barged to the port site and pumped to upland storage facilities with a capacity of approximately 400,000 gallons. Fuel would be transported by truck from these storage tanks to the mine location (National Park Service, 1999a). Obvious environmental concerns related to accidental petroleum spills will exist during the life of the mining operation. Along with the threat of petroleum spills, contamination may leach from ore stockpiles into local streams (i.e., Johnson River, Bear Creek). Erosion problems (e.g., accelerated soil loss, increased stream turbidity) could also develop along access roads. To provide some baseline information for this high-profile area, the U.S. Geological Survey and NPS are collecting geochemical data from the Johnson River watershed and monitoring Johnson River discharge at a telemetered gaging station. There are other potential mining activities in the region that also pose natural resource concerns for LACL. For example, Cominco, an international mining corporation, has filed state mining claims on the Pebble/Copper deposit north of Lake Iliamna. If developed, this open pit mine would be the largest in Alaska. Although development would occur 15 miles southwest of LACL, direct impacts on air and water quality may have substantial effects on park resources (National Park Service, 1999a).

Source National Park Service, Water Resource Division


Alaska Geographic Society. 1986. Lake Clark - Lake Iliamna Country. Vol. 13, No. 4, Anchorage, AK pp. 16-45.

Bayha, K., S. Lyons , and M.L. Harle. 1997. Strategic Plan for Water Resources Branch U.S. Department of Interior; Fish and Wildlife Service, Region 7, Division of Realty, Water Resources Branch, WRB 97-1. Anchorage , AK , 25 pp.

Brabets, T., 2000. Personal Communication. U.S. Geological Survey, Water Resources Division. Anchorage , AK .

Chaniberlain, D.M. 1989. Physical, and Biological Characteristics and Nutrients Limiting Primary Productivity, Lake Clark , Alaska . (unpubl. Master thesis) Michigan Technological University . Houghton , MI 139 pp.

Dale, B. and R Stottlemyer. 1986. Chemical, Physical and Biological Characteristics of Lake Clark and Selected Surface Waters of Lake Clark National Park and Preserve, Alaska. GLARSU Report #17. Michigan Technological University, Dept. of Biological Sciences. Houghton, MI. 23 pp.

Dorava, J.M. and A.M. Milner. 1999. Effects of Recent Volcanic Eruptions on Aquatic Habitat in the Drift River, Alaska, USA: Implications at Other Cook Inlet Region Volcanoes. Environmental Management 23(2):217-230.

Hampton, M.A. 1982. Synthesis Report: Environmental Geology of Lower Cook Inlet, Alaska. U.S. Geological Survey, Open-File Report 82-197. Melano Park, CA. 55 pp.

Ivanhce, L.F. 1962. Right-lateral strike-slip movement along the Lake Clark fault, Alaska: Geol. Soc. of Am. Bull., v. 73. pp. 911-912.

Kienle, J. and S.E. Swanson. 1983. Volcanism in the Eastern Aleutian Arc: Late Quaternary and Holocene Centers, Tectonic Setting and Petrology. [In] B.H. Baker and A.R McBirney (eds.), Jour. of Volcanology and Geothermal Research 17:393-432.

National Park Service, 1999a. Resources Management Plan, Lake Clark National Park and Preserve. Draft revision to approved 1994 plan. Anchorage, AK. 171 pp.

Prowse, T.D. and R.L. Stephenson, R.L. 1986. The Relationship Between Winter Lake Cover, Radiation receipts and the Oxygen Deficit in Temperate Lakes. Atmos.-Ocean 24:386-403.

Prowse, T.D. 1994. Environmental Significance of lee to Streainflow in Cold Regions. Freshwat Biol. 32:241-259.

Rouse, W.R., M.S.V. Douglas, RE. Hecky, A.E. Hershey, G.W. Kling, L. Lesack, P. Marsh, M. McDonald, B.J. Nicholson, N.T. Roulet, and J.P. Smol. 1997. Effects of Climate Change on the Freshwaters of Arctic and Subarctic North America. [In] M.G. Anderson, N.E. Peters, D. Walling (eds.), Hydrological Processes. 2:873-902.

Stottlemyer, R 1990. Preliminary Assessment of Change in Limnology of Lake Clark Following Input of Volcanic Ash from Redoubt Volcano. Great Lakes Area Resource Studies Unit Report #45. Michigan Technological University, Houghton, MI. 12 pp.

Till, A.B., M. E. Yount, and J.R Riehle.1992. Redoubt Volcano, Southern Alaska: A Hazard Assessment Based on Eruptive Activity through 1968. U.S. Geological Survey Bulletin 1996.19 pp.

U. S. Department of the Interior. 1952. Alaska, A Reconnaissance Report on the Potential Development of Water Resources in the Territory of Alaska for Irrigation, Power, Production and Other Beneficial Uses. U.S. Bureau of Reclamation, Alaska District Office. House Document 197, 82" d Congress. pp. 160-162.

Wild, Spectacular Scenic Diversity
Lake Clark National Park and Preserve is a composite of ecosystems representative of many diverse regions throughout Alaska. The spectacular scenery is unrivaled. The recreational opportunities are varied and plentiful. Although continuously inhabited since early prehistoric times, the area remains wild and sparsely populated, with aircraft providing the primary means of access. Within the park the mountains of the Alaska and the Aleutian Ranges join. The Chigmits, an awesome, jagged array of mountains, are the result of centuries of

  • uplifting,

  • intrusion,

  • earthquakes,

  • volcanism, and

  • glacial action.
Two active volcanoes, lliamna and Redoubt, form an important link in the Pacific "ring of fire". Venting steam, snow-capped, and rising more than 3,050 meters (10,000 feet), each is an impressive volcano to be viewed from the eastern side of the park.

The range's eastern flank descends rapidly to Cook Inlet. Rivers cascade dramatically to the sea through forests of Sitka and white spruce. The coastal cliffs, holding fossil remnants of 150 million years of sea life, are stark counterpoints to the active volcanoes and glacial streams that are reshaping the landscape. On marshes and outwash plains, swans and other waterfowl nest. The rocky cliffs in and adjacent to the park provide rookeries for puffins, cormorants, kittiwakes, and other seabirds. Seals and whales may occasionally be observed off shore.

The western flank of the Chigmit Mountains descends through tundra covered foothills to boreal forest. Spectacular lakes and wild rivers fill the valleys, flowing southwestward to Bristol Bay. Fish include five species of salmon, rainbow trout, Dolly Varden, lake trout, northern pit and arctic grayling. Dan sheep, caribou, and moose forage the area. Brown and black bear are present, as well as wolves, lynx, foxes, and other mammals.

This western side of the park and preserve provides many recreation opportunities:

  • Anglers find trophy fish;

  • hikers explore high tundra slopes;

  • river runners thrill to the Tlikakila, Mulchatna, or Chilikadrotna Wild Rivers; and

  • campers find lakeshore sites inspirational.

This vast area also may be harsh. Planning and preparing for a wilderness experience is critical to the enjoyment of the area in all conditions: wind, rain, snow, and sunshine.

Winter is long-October through April. In some locations the sun does rise above the peaks for several months. A fresh snow can veil the area majestically or winter winds may uncover a landscape of subtle brown highlighted by ice-blue frozen lakes. Break-up in spring can immobilize the area, as ice melts and frozen ground turns to mud. Summer is the time of life as caribou calve, buds turn to leaves, mosquitoes hatch, and salmon return to spawn. Clouds often cap the Chigmit Mountains and occasionally close the passes to aircraft. Precipitation is about a third less on the west side, but everywhere rain produces a summer floral display. Fireweed, lupine, blueberry, and berry abound. In autumn the burgundy hued tundra blankets the slopes around aptly named Turquoise Lake. A light dusting of snow over fellow birch and red bearberry produces a truly rare visual pleasure.

The area has been occupied since prehistoric times and archeological investigations are continuing to trace early settlement. Dena'ina Indians lived in villages at Kijik and Old Village until the early 1900s, when they moved to Nondalton and other sites. Russian explorers, traders, and missionaries began traversing the region in the 1790s. The salmon industry began attracting American and foreign settlers in the early 1900s. Around Lake Clark most were trappers and miners. Recent years have produced an economy based on subsistence lifestyles, commercial fishing, and recreation activities.

Lake Clark National Park and Preserve was established on December 2, 1980. The park contains approximately 1 million hectares (2.6 million acres); the preserve contains 565,000 hectares (1.4 million acres). Wilderness designation has been placed on 970,000 hectares (2.4 million acres) of the total.

park maps subheading

The General park map handed out at the visitor center is available on the park's map webpage.

For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.

photo album subheading

A photo album for this park can be found here.

For information on other photo collections featuring National Park geology, please see the Image Sources page.

books, videos, cds subheading

Currently, we do not have a listing for a park-specific geoscience book. The park's geology may be described in regional or state geology texts.

Please visit the Geology Books and Media webpage for additional sources such as text books, theme books, CD ROMs, and technical reports.

Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
ISBN 0-393-92407-6
9" x 10.75", paperback, 550 pages, full color throughout

The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!

Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.

geologic research subheading

For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.

The NPS maintains a searchable data base of research needs that have been identified by parks.

A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.

selected links subheading

NPS Geology and Soils Partners

NRCS logoAssociation of American State Geologists
NRCS logoGeological Society of America
NRCS logoNatural Resource Conservation Service - Soils
USGS logo U.S. Geological Survey

teacher feature subheading

Currently, we do not have a listing for any park-specific geology education programs or activities.

General information about the park's education and intrepretive programs is available on the park's education webpage.

For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.
updated on 01/04/2005  I   http://www.nature.nps.gov/geology/parks/lacl/index.cfm   I  Email: Webmaster
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