Geohazards in Alaska’s National Parks

Chad Hults, Denny Capps, and Eric Bilderback, National Park Service
A map of Alaska showing earthquakes and their depth, volcanoes, and plate tectonics.
Figure 1. Map showing earthquake epicenters for earthquakes greater than magnitude 3.0 since 1889 (http://www.aeic.alaska.edu).

Major faults (young and old) are shown as black lines, and active volcanoes are shown as black triangles. The Pacific Plate motion relative to the North American plate is shown with arrows.

Alaska is the most geologically active part of North America. Active plate tectonics creates the high topographic relief and aggressive erosion by gravity, glaciers, rivers, and weathering creates unstable slopes. Southcentral Alaska overlies the subduction zone of the Pacific Plate where earthquakes are frequent and often high magnitude (Figure 1). Plate tectonics along with isostatic rebound result in rapidly uplifting mountains. For example, the Wrangell-St. Elias and Glacier Bay areas are uplifting at a rate of more than 0.75 inches (2 cm) a year (Larsen et al. 2004). Geohazards include earthquakes, landslides, rockfall, debris flows, glacier outburst floods, ice and snow avalanches, river erosion and deposition, and other hazards associated with geological processes. The active tectonics and extreme climatic processes combine to make geohazards common in Alaska.

Much of the mystique of Alaska is its essence of wilderness where the land is expected to be wild and unpredictable. The awe-inspiring landscape, harsh climate, and obvious forces of nature make it an exciting tourist destination. As such, geohazards are expected as a part of life, or even a badge of honor, for those who can overcome their challenges. With the expectation of Alaska being wild, it is often hard to justify diverting valuable resources to study a process that occurs infrequently. Furthermore, because Alaska's parks have so many types of geohazards, it can appear futile to attempt managing the potential risk.

It is often the case in the remote Alaska parks that geohazard events unfold without notice. For example, the massive Taan Inlet landslide and tsunami in Wrangell-St. Elias National Park and Preserve was not noticed until researchers detected it on seismometers and confirmed it by satellite imagery days later (see The 2015 Taan Fiord Landslide and Tsunami). No people were present, so no one was at risk. Only a remote airstrip was destroyed by the tsunami. Without exposure to a geohazard, there is no risk. However, events like this are occurring more frequently in Alaska parks, so it is important to recognize the nexus where infrastructure or people are exposed to geohazards.

In this issue of Alaska Park Science, the scientists that study geohazards present where they may occur, what we know about the processes influencing them, and what can be done to improve safety and resiliency. After reading these articles, a reader will better understand the state of the science for geologic and climatic processes that cause geohazards. Geohazards exist with or without resources, infrastructure, or humans present. The hazard level is a function of the frequency of events and their magnitudes. Risk is a function of the probability of a geohazard, but also exposure levels, vulnerability, and resiliency. Although the exact timing of most geohazards is hard to determine, the areas at risk can be identified (mapped) and our vulnerabilities to these hazards can be assessed. Only with this knowledge can we manage our exposure and develop resilient systems to protect people and infrastructure from geohazards.

People are generally poor at assessing the risk of low-frequency events, even if they potentially pose catastrophic consequences. It is often the case that while hazards are recognized by geologists, the extent of a geohazard is understood only after catastrophic events. The National Park Service’s (NPS) mission includes preserving naturally occurring geologic processes. The NPS also has a responsibility to protect people as well as park resources. The NPS policy states: “The Service will work closely with specialists at the U. S. Geological Survey and elsewhere, and with local, state, tribal, and federal disaster management officials, to devise effective geologic hazard ident-ification and management strategies” (NPS 2006, Section 4.8.1.3). While the NPS is charged with unimpaired preservation of naturally occurring geologic processes and scenery, risk reduction is also a central management strategy. This Alaska Park Science issue was created to highlight the state of the knowledge about geohazards as a park management issue and to better inform decision makers and the public.

Geohazards in Alaska’s Parks

Geohazards are present in every park in Alaska (Table 1). Some parks were formed due to geohazards; for example Aniakchak National Monument was created after the 1931 eruption of Aniakchak, and Katmai National Monument was created after the 1912 eruption of Novarupta (see Volcanic Ash Resuspension from the Katmai Region). The NPS also manages the National Natural Landmarks program that includes landmarks formed by geohazards (see Volcanic Hazards in Alaska's National Parks),

Table 1. General exposure levels of Alaska parks to geohazards. These preliminary estimates are based on the likely presence of a significant magnitude and frequency of the geohazard events and the coincidence of the geohazards with park infrastructure and people.
Park Landslide Tsunami Glacial Lake Outburst Flood Volcano Earthquake River Breakup River Erosion Coastal Erosion
Sitka NHP Moderate High No Low High No Moderate Moderate
Glacier Bay NP&Pres High High Moderate No High No Low Low
Klondike Gold Rush NHP High Moderate Moderate No Moderate No High Low
Wrangell-St Elias NP&Pres High High Moderate High High Low Moderate Moderate
Kenai Fjords NP High High High Low High No Moderate Low
Aniakchak NM Moderate High No High High No Moderate Moderate
Katmai NP&Pres Moderate High Low High High No Moderate Moderate
Lake Clark NP&Pres Moderate Moderate Low High Moderate Low Moderate Moderate
Denali NP&Pres High No Low Low High Low Moderate No
Yukon-Charley Rivers NPres Moderate No No No Low High High No
Gates of the Arctic NP&Pres Moderate No No No Low Low Moderate No
Noatak NPres Moderate No No No Low Low Moderate No
Kobuk Valley NP Low No No No Low Low High No
Cape Krusenstern NM Low Low No No Low Low Low High
Bering Land Bridge NPres Low Low No No Low Low Moderate High
NHP=National Historical Park; NM=National Monument; NP=National Park; NP&Pres=National Park and Preserve; NPres=National Preserve

For each type of geohazard in Alaska, there are government agencies developed to study, evaluate, and warn the public about geohazards. For some geohazards, there are robust monitoring systems in place that can provide early warning to help save lives. For example, the Alaska Volcano Observatory conducts studies to understand the eruptive histories and the potential hazards of active volcanoes. They have a monitoring system of seismometers, infrasound microphones, and satellite data that geophysicists use to detect eruptions and send notifications through a widely available warning system. In contrast, there are other geohazards, like landslide-generated tsunamis that are less understood and are not actively monitored.

Landslide-generated tsunamis have occurred in Alaska parks and some have killed people, but the areas with landslide potential have yet to be mapped, so the risk to visitor safety from landslide-generated tsunamis is largely unknown. Although massive landslide events are low frequency, the warming climate appears to be increasing the frequency of these events (see Geohazard Risk Reduction along the Denali National Park Road; An Initial Assessment of Areas Where Landslides Could Enter the West Arm of Glacier Bay, Alaska and Implications for Tsunami Hazards; The 2015 Taan Fiord Landslide and Tsunami; and Catastrophic Glacier Collapse and Debris Flow at Flat Creek, Wrangell-St. Elias National Park and Preserve). Therefore, the known history of landslide events may not be useful for quantifying the frequency and magnitude of future events. Particularly for large landslides, the historic record in Alaska goes back less than a century. Also, places prone to landslide-generated tsunamis are in steep fjords that have only recently been deglaciated. For example, Icy Bay was completely glaciated in the 1950s, yet a significant landslide-generated tsunami occurred only a couple decades after the Taan Inlet glacier retreated. The potential for landslide-generated tsunamis in these areas is increasing because recent deglaciation is debutressing slopes; thawing high-altitude permafrost is reducing the shear strength of the rocks; and precipitation in the form of rain, rather than snow, is increasing pore pressures in the soils. In addition to these geologic processes, visitation rates are increasing, which is increasing exposure to risk. Mapping areas prone to landslides and landslide-generated tsunamis, and a quantification of the exposure, vulnerabilities, and resiliency, are necessary to reduce the risks to infrastructure and lives.

Denali National Park and Preserve provides a good example of how increasing landslide frequency has led to management actions to reduce risk. Denali has a long history of landslides impacting the park road and steps have been taken to address those hazards (Geohazard Risk Reduction along the Denali National Park Road). Recently, the frequency of landslides appears to be increasing, possibly due to thawing permafrost. In response, Denali, together with the Federal Highways Administration, U.S. Geological Survey, numerous academic institutions, consultants, and others, developed an unstable slope management program for the park road. They have quantified and are tracking over 140 unstable slopes and are beginning to systematically improve safety and resiliency of the highest ranking sites.

Visitor and employee safety has precedence in NPS policy (NPS 2006). It is important that employees are trained so that they are empowered and prepared to provide safe access and effective disaster response. The NPS has a robust incident command system with people ready to respond, but also need plans for each geohazard type. These management plans would generally include:

  • Identifying the geohazard (historic events or features).
  • Mapping areas of potential geohazards.
  • Understanding the processes that lead to the geohazard or its initiation.
  • Quantifying the frequency and magnitude of a geohazard event.
  • Developing monitoring/detecting tools.
  • Conducting a vulnerability assessment of the threatened infrastructure or people.
  • Creating plans for avoiding and responding to geohazards.
  • Educating employees and visitors of the geohazards in the parks.

Only through knowledge of potential geohazards are we able to reduce their risks. Newly accessible technologies like interferometric synthetic aperture radar (InSAR), light detection and ranging (LiDAR), structure from motion, and repeat high-resolution satellite imagery make identifying and mapping areas prone to geohazards easier, and makes monitoring geohazards more cost-effective. With accessible technologies, the areas prone to geohazards are identifiable and monitorable (for example, see Risk and Recreation in a Glacial Environment: Understanding Glacial Lake Outburst Floods at Bear Glacier in Kenai Fjords National Park).

Alaska’s active tectonics and warming climate are not slowing down. Processes like volcanic eruptions (see Volcanic Hazards in Alaska's National Parks) or earthquakes (see Addressing Earthquake and Tsunami Hazards in Alaska Parks) are deep-Earth processes that are not influenced by humans; however, climate change is increasing the frequency of landslides (see Geohazard Risk Reduction along the Denali National Park Road; An Initial Assessment of Areas Where Landslides Could Enter the West Arm of Glacier Bay, Alaska and Implications for Tsunami Hazards; The 2015 Taan Fiord Landslide and Tsunami), storms hitting the Arctic coast (see Coastal Dynamics in Bering Land Bridge National Preserve and Cape Krusenstern National Monument), and changing the timing and dynamics of river breakup (see Spring Breakup on the Yukon: What Happens When the Ice Stops).

Geohazards themselves may not be manageable, but with increased knowledge and commitment, many of the risks to infrastructure, resources, and human safety are. Although every park in Alaska contains some type of geohazard, they don’t occur everywhere. Where the nexus of geohazards and exposure exist, the NPS, together with other federal agencies and partners, has a role in gathering necessary data and communicating what we know to employees and the public. The articles in this issue of Alaska Park Science highlight some spectacular events that occurred in Alaska parks, describe the processes leading up to those events, and discuss what we can do to reduce the risks associated with geohazards.

References


Larsen, C. F., R. J. Motyka, J. T. Freymueller, K. A. Echelmeyer, and E. R. Ivins. 2004.
Rapid uplift of southern Alaska caused by recent ice loss. Geophysical Journal International 158: 1118–1133. doi:10.1111/j.1365-246X.2004.02356.x.

National Park Service (NPS). 2006.
Management Policies 2006: A guide to managing the National Park System. U.S. Department of the Interior, 168 p. Available at: https://www.nps.gov/policy/mp/policies.html (accessed June 20, 2019)

Last updated: December 30, 2019