Developing effective warning systems: Ongoing research at Ruapehu volcano, New Zealand

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Abstract

Purpose

This paper examines the unique challenges to volcanic risk management associated with having a ski area on an active volcano. Using a series of simulated eruption/lahar events at Ruapehu volcano, New Zealand, as a context, a model of risk management that integrates warning system design and technology, risk perceptions and the human response is explored.

Principal results

Despite increases in the observed audibility and comprehension of the warning message, recall of public education content, and people's awareness of volcanic risk, a persistent minority of the public continued to demonstrate only moderate awareness of the correct actions to take during a warning and failed to respond effectively. A relationship between level of staff competence and correct public response allowed the level of public response to be used to identify residual risk and additional staff training needs. The quality of staff awareness, action and decision-making has emerged as a critical factor, from detailed staff and public interviews and from exercise observations. Staff actions are especially important for mobilising correct public response at Ruapehu ski areas due to the transient nature of the visitor population. Introduction of education material and staff training strategies that included the development of emergency decision-making competencies improved knowledge of correct actions, and increased the proportion of people moving out of harm's way during blind tests.

Major conclusions

Warning effectiveness is a function of more than good hazard knowledge and the generation and notification of an early warning message. For warning systems to be effective, these factors must be complemented by accurate knowledge of risk and risk management actions. By combining the Ruapehu findings with those of other warning system studies in New Zealand, and internationally, a practical five-step model for effective early warning systems is discussed. These steps must be based upon sound and regularly updated underpinning science and be tied to formal effectiveness evaluation, which is fed back into system improvements. The model presented emphasises human considerations, the development of which arguably require even more effort than the hardware components of early warning systems.

Introduction

Volcanic risk is the product of human interaction with a natural physical process. It is generally accepted that public hazard education, communication and engagement of those at risk provides an essential foundation to effective risk management and the development of community resilience (Johnston et al., 1999, Johnston et al., 2000, Paton et al., 2001, Twigg, 2002, Gregg et al., 2004). In most communities where volcanic risk exists, risk management involves a relatively stable population to whom risk communication can be directed and for which risk management strategies can be developed over time. This stability is, however, not always present.

Mount Ruapehu, an andesitic stratovolcano near the southwestern terminus of the Taupo Volcanic Zone, in the North Island of New Zealand (Fig. 1) erupts on average roughly every 10 to 50 years. The last major eruptive episode spanned 1995–96 (Houghton et al., 1996).

Since 1945, eruptions large enough to be hazardous to people (i.e. launching projectiles or lahars beyond the immediate vicinity of the crater) have occurred at intervals of 2 to 14 years (Hackett and Houghton, 1989, Keys, 2007). Hydrothermal eruptions occurred in October 2006 and September 2007. The presence of a crater lake and ski areas on Ruapehu gives rise to a potential risk from lahars — debris flows, transitional flows or hyperconcentrated flows originating at a volcano (Vallance, 2000).

There are two main types of lahar hazard at Ruapehu: lahars from the breakout of Crater Lake into the Whangaehu River, and eruption-generated lahars in other catchments, including those feeding into ski areas. The social research presented in this paper focuses on the management of the volcanic risk at Whakapapa ski area.

The existence of a ski area at Ruapehu volcano, New Zealand, means that the population at risk is transient and can change on a daily basis, and poses a particular challenge for volcanic risk management. Using a series of simulated eruption/lahar events at Ruapehu volcanic, New Zealand, as a context, this paper discusses how integrating warning system design and technology with human-response characteristics can inform the development of an effective risk management strategy. The results of this work are integrated with those of other warning system studies in New Zealand and internationally to adapt a practical model (Sections 2 and 3) of effective early warnings to the unique situation at Ruapehu that must cater for a transient population (e.g., skiers and tourists/sightseers, Sections 4 through 6). The Ruapehu results also act to highlight the importance of work beyond the generation and notification of a warning message necessary to achieving effective warning response.

The presence of the ski area on Ruapehu introduces two significant human components. One comprises those employed to run ski area operations. The other is the population of skiers. The transient nature of the latter makes them considerably more dependent on the emergency responders (i.e., ski area staff in this case) to guide their effective response to a warning than would be the case in most other situations in which hazard warning systems are developed. This paper thus brings a unique perspective to the risk management literature, outlining work that has been undertaken to understand how the relationship between ski area staff and the public can be incorporated into the warning system.

In most cases where warnings systems are included in volcanic risk management programs, their development involves the relationship between scientific and technical sources and professional emergency managers. However, at Ruapehu, there is a direct relationship between scientific sources and ski area staff who are not previously trained in emergency management.

The lahar risk to Whakapapa ski area is often confused with the more-widely publicised risk in the Whangaehu River channel. Most moderate or larger eruptions eject water from Crater Lake into the Whangaehu River catchment, often forming lahars. During the 1995–96 eruption episode Crater Lake was emptied for the first time since 1945, with numerous lahars flowing down the Whangaehu. A layer of tephra was deposited over the natural lake overflow channel on the southern crater rim at the head of the Whangaehu River valley (Fig. 2), creating a natural dam and the potential for a hazardous breakout flood in this valley. The break out lahar occurred on the 18th of March, 2007, causing no injury to people and virtually no damage to infrastructure. A similar lahar during the 1953 ‘Tangiwai’ event resulted in the death of 151 train passengers when a lahar damaged a rail bridge. Breakout lahar events pose no hazards to any of the ski areas (Leonard et al., 2004). Lahars in the Whangaehu may also result from collapse of the Crater Rim itself or from hydrothermal areas.

Ruapehu is part of Tongariro National Park, administered by the Department of Conservation (DoC) who recommended that no engineering intervention at the tephra barrier be allowed (Department of Conservation, 1999). Instead they recommended (a) the development of a warning and response system, (b) the development of revised land-use and hazard response plans in potential lahar zones and (c) further investigation of a levee (reviewed in Hancox et al., 2001) near the spill-over point of the Whangaehu River into the Tongariro River which drains to Lake Taupo. Of these recommendations, the levee was completed in early 2002, around the same time that the Eastern Ruapehu Lahar Alarm & Warning System (ERLAWS) was put in place (Section 1.3). The overall system of risk mitigation (plans, structure and other actions) is summarised by Keys (2007). This includes revised event response plans and modification of land-use. Once the overall system was in place the residual risk was low and intervention at the crater was considered unnecessary by the Government.

The risk-mitigation planning process has been analysed in detail by Galley et al. (2004) and the following is a brief summary from that work. Response plans have been prepared by local government and other stakeholders for areas likely to be affected by lahars in the Whangaehu River. Some of the organisations developed an “all-hazards” approach to response planning, with many components applicable to a range of hazards, rather than planning specifically for the dam-break lahar. More organisations will hopefully follow this approach in the future. The all-hazard approach enhances future response capability, and allowed the actual break out to act as a case study for integrated emergency management.

The lahar response process is complicated by the geographic extent of the affected area, and the consequent multi-agency and multi-jurisdictional context in which response will occur. Strategies that accommodate multiple entities within the warning process drew on analyses of the inter-organisational response conducted following the 1995 and 1996 eruptions (Paton et al., 1998, Paton et al., 1999).

The communications and coordination issues (e.g., terminological issues, lead agencies etc.) raised are rendered more complex by the functional boundaries between agencies (e.g. Police and DoC), and the need for them to be resolved in ways that allow collective action so that each can achieve its goals and objectives. The recommended multi-agency planning approach was an effective management strategy for the lake breakout event. However, maintaining a high level of communication and coordination for an uncertain period created other planning issues (e.g., civic agencies have to allocate resources to maintaining readiness, including re-training for staff fulfilling response roles). As time passed, it became more likely that key people would move on or need backup and succession planning became important.

Mount Ruapehu hosts three ski areas. Whakapapa, on the northern slopes, is New Zealand's largest and is at risk from several volcanic hazards from Mt Ruapehu, depending on the size of eruption, and seasonal and weather conditions. These include base surges, ballistic block and bomb falls, lahars, ash fall and in some pre-historic eruptions lava flows. Warning system design is rendered complex by the fact that the populations at risk are predominantly transient recreational skiers and tourists who, if on the topmost ski runs, are 1.5 to 2 km from Crater Lake. There are several types of volcanic hazard, but the greatest volcanic hazard to property and life on Whakapapa ski area is from lahars and many of these happen without useful precursors.

The crater rim to the north and west of the lake, in the direction of Whakapapa and Turoa ski areas, is significantly higher than to the east and south, so moderate eruptions are likely to create small lahars in Whakapapa ski area only during strong southerly winds (Otway et al., 1995) or directed blasts as on 23 September 1995 and 25 September 2007. Historically, lahars have not been seen within Turoa ski area, but cannot be ruled out there in future. Tukino ski area is unlikely to receive lahars in all but the largest summit eruptions as it is farther away, and is not in a direct drainage path, from the mountain summit. Current warnings research is focusing on Whakapapa ski area, but will in future expand at least to include Turoa ski area.

The recurrence intervals for moderate (≥ 105 m3) and large (≥ 106 m3) historical eruptions have been estimated at ∼ 10 years and 27 years, respectively. From stratigraphic evidence, the recurrence interval of very large (≥ 107 m3) pre-historic eruptions (before European settlement in the mid-19th century), is 55 to 100 years (Otway et al., 1995). Such a very large eruption has not been documented since European settlement. Large and very large eruptions usually send moderate to large lahars down Whakapapa ski area. Very large-eruption lahars would probably badly damage some ski area structures, whereas large-eruption lahars are unlikely to cause much damage, as current National Park policy requires that all structures must be built away from lahar paths or, if not, be strong enough to withstand lahars. This policy was introduced following the 1969 and 1975 large eruptions in which lahars damaged both lifts and buildings on the ski area (Fig. 3) (Healy et al., 1978, Nairn et al., 1979). Lahars from the large eruption on 23 rd September 1995 entered the ski area within 90 s, but narrowly missed damaging any structures (Fig. 4). Events in 1995 led to the re-development of a warning system, and focused consideration on the human element.

There are two lahar warning systems at Ruapehu, the Eastern Ruapehu Lahar Alarm & Warning System (ERLAWS) and the Eruption Detection System (EDS). The ERLAWS system monitored Crater Lake natural dam collapse but remains in place for future lahars in the Whangaehu River channel and automatically alerts emergency responders. The EDS monitors eruptions and broadcasts automated lahar warning messages across Whakapapa ski area. Both systems are operated, maintained and primarily monitored by DoC with support from GNS Science and GeoNet. GeoNet is the GNS Science national geohazards monitoring project core funded by the New Zealand Earthquake Commission (EQC). GeoNet duty scientists monitor ERLAWS and the EDS as a backup to the automated systems.

The installation of a permanent lahar warning system provides long-term early warning for eruption-triggered and other lahars in the Whangaehu River valley, no matter how they formed (Keys, 2007). It comprises two geophones (vibration sensors) each at two sites spaced down the channel on the upper flank of the mountain. While the dam existed it also included three geophones in or near the dam, a tripwire across the barrier and a Crater Lake level sensor. Automated telemetry triggers pager and telephone activation of an emergency management response plan (Section 5).

The current Eruption Detection System (EDS) for Whakapapa ski area (which also feeds into the wider national GeoNet volcano monitoring system) consists of continuous real-time radio-telemetered monitoring (Sherburn and Bryan, 1999) of:

  • (1)

    seismicity at the summit of Ruapehu via the seismometer in Dome Shelter, the seismometer at Far West T-Bar site and data from other seismometers in the existing regional earthquake monitoring network; and

  • (2)

    barographs (specialised microphones) on the upper mountain to detect the shock wave produced by an eruption.

An automatic computer-based analysis of data from the EDS sensors determines when an eruption is occurring that is likely large enough to generate a lahar at Whakapapa ski area (Sherburn and Bryan, 1999). It can distinguish volcanic from volcano-tectonic earthquakes, and corroborates this with any barograph detection of a blast. When a likely-lahar-forming eruption is detected, the EDS automatically triggers broadcast via loud-speakers across the ski area alternating sirens and pre-recorded announcements instructing the correct course of action. These broadcasts are designed to be audible across the entire ski area, but particularly in high-risk areas, and an additional warning signal is transmitted to DoC and key ski area staff to indicate a lahar threat is present. DoC and GNS Science GeoNet staff can also remotely monitor, access and program the system at any time (Sherburn and Bryan, 1999).

Section snippets

Risk perception, resilience and warning system effectiveness

To understand people's decision-making and response to warnings, two issues are relevant: the reception of warning messages in a timely manner, and the relationship between warnings and capacity to respond. It is generally assumed by emergency management agencies that warnings will be treated at face value, accepted and acted upon. This assumption is not, however, always justified. For example, recent research on tsunami warnings (Johnston et al., 2005) found that people may choose not to

Effective early warning systems: developing a practical five-step model

An effective warning system must be underpinned by good (a) natural process and hazard event research (e.g., identifying the source and nature of the lahar risk in a specific area); and (b) impact research (e.g., hazard maps) and vulnerability research. Globally, the proportion of this latter ‘applied’ research published is greatly outweighed by the volume of the former ‘pure’ research (Chester et al., 2002). At Ruapehu, a range of natural processes and hazard event research has been undertaken

Social research

Social research into effectiveness of both warning systems at Ruapehu has to date included:

  • (1)

    an analysis of emergency response arrangements (Galley et al., 2004);

  • (2)

    a baseline set of interviews of response expectations among emergency personnel (just completed with results still to be interpreted);

  • (3)

    surveys of public perceptions of risk and warnings in 2000 (Galley et al., 2003), 2003, 2004 and 2005 — Table 2 and Fig. 6, Fig. 7, Fig. 8, Fig. 10, Fig. 11 present the sample characteristics and results

Whakapapa ski area risk perception and eruption-generated lahars

Risk perception surveys were conducted to compare risk perception to education campaigns and evacuation compliance rates in simulation exercises and tests. Almost all respondents (> 94%) in the six surveys were aware that Ruapehu is an active volcano. The perceived timing of the next volcanic event at Ruapehu has varied from survey to survey (Fig. 6). The large majority of people in all surveys have consistently stated that the next event would be within their lifetime, with the majority

Observations of simulation exercises and ‘blind’ tests

During each of the six simulation exercises and blind tests to date, observers have been stationed in key locations across the ski area to assess audibility and staff and public response to the EDS. The public were also interviewed after the test to add supplementary observations of audibility and public actions across the field. Ward et al. (2003) provide a summary of comments from the 2001 survey which are incorporated with the subsequent five datasets in the analysis here.

Conclusions

There is a substantial amount of work, beyond the generation and notification of an early warning message, required to achieve an optimum rate of correct decision-making and action based upon that warning. The practical five-step model discussed here for effective warning systems emphasises these additional considerations, which arguably require even more effort than the hardware component of early warning systems. We have seen at Ruapehu that high levels of risk perception, or even

Acknowledgements

This manuscript benefited from the constructive reviews and recommendations of J. Ewert and one anonymous reviewer. The authors appreciated the partnership and support of Ruapehu Alpine Lifts and the Ruapehu Mountain Clubs Association (Inc.). The research at Ruapehu was funded by the Foundation for Research Science and Technology with contribution from the Department of Conservation.

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    Present address: University of Alberta, Department of Earth & Atmospheric Sciences, 1-26 Earth Sciences Building, Edmonton, Alberta T6E 2E3, Canada.

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