Know the difference between a red or yellow tsunami evacuation zone in Hawaii?
Residents who live in red areas of the map, mostly along coastlines and harbors, are in the tsunami evacuation zone and are required to evacuate during a warning such as the one issued in July. Those in the yellow, or extreme tsunami evacuation zone, however, are not.
But this distinction may have been lost by many Hawaii residents scrambling to respond to a July 29 tsunami warning following an 8.8-magnitude earthquake off Kamchatka, Russia. The result was islandwide traffic gridlock as thousands of residents attempted to leave coastal areas and get to higher ground via Oahu’s limited number of corridors.
Randal Collins, director of the Honolulu Department of Emergency Management, said, “We tell the public this: For most tsunami warnings, evacuate the red zone. For an extreme tsunami warning, evacuate both red and yellow zones.”
Collins added, “Extreme tsunami warnings are rare, but we will always use the word ‘extreme’ when both zones must evacuate. If you don’t hear ‘extreme,’ the evacuation area only pertains to the red zone only. We educate the public about this protocol through our website, at outreach events, with printed maps, and during media appearances during and after evacuation events. Simple and consistent.”
While some residents understood, others were confused, according to Collins, saying the department heard of both reactions.
“The feedback from the community has been mixed, which tells us we need to do better,” he said. “We take responsibility for improving education on the tsunami zones, but at the same time, we ask the public to do their part.”
The public can look up their evacuation zones on multiple websites online, including at honolulu.gov/tsunamievac, or in the first few pages of their phone book.
Extreme tsunami zone
So what is the extreme tsunami zone?
The extreme tsunami zone — the area of map highlighted in yellow — was added in 2015 for a tsunami generated by a more rare, but plausible, earthquake of 9.0-magnitude or greater in the Eastern Aleutian Islands, according to officials.
Such an earthquake would provide the least evacuation preparation time, about 4 to 5 hours, for Hawaii residents.
Kwok Fai Cheung, a coastal engineering professor at the University of Hawaii at Manoa, drew the boundaries for the “extreme evacuation zone.”
First, he said it was important to understand the Tier 1 zone (red zone) is based on the worst-case scenarios of tsunamis that have occurred during the past 200 years.
A Tier 1 warning is triggered by a coastal wave amplitude — or wave height — of over 3 feet. In a Tier 1 evacuation, the tsunami is expected to be big enough to wash across the beach and possibly flood into the first block.
For Tier 2 (yellow zone) maps, Cheung and his associates moved boundaries farther inland to reflect a more disastrous event.
Cheung said he worked with a seismologist to develop the worst-case scenario for Hawaii from both a 9.3- and a 9.6-magnitude Aleutian earthquake.
One creates more compact waves, while the other has more energy and longer waves, but both are potentially destructive for the state. Combined, they served as the criteria for models used to draw up the “extreme evacuation” zone.
In Honolulu, for instance, Ala Moana Regional Park is in a red zone, while Ala Moana Center is in a yellow zone. Blaisdell Center and McKinley High School are also in the yellow zone.
Emergency officials said they got a wake-up call after the March 11, 2011, earthquake and tsunami in Japan, and realized they needed to plan for the possibility of more extreme events.
A 9.0-magnitude earthquake that struck off the coast of Honshu, Japan, generated a tsunami that arrived on the country’s coast within 30 minutes, killing nearly 20,000 victims.
Thousands of miles across the ocean, no lives were lost in Hawaii, but the 2011 tsunami was highly destructive, causing $31 million in damages.
The destruction was far worse than expected, Cheung said, even though Japan had 100 years of tsunami history as criteria for engineering, design and evacuation planning.
“So we realized, we need to prepare for something we have not seen, so we will not be caught by surprise,” he said.
Some 200 years of data is really “just a snapshot”of geologic history on Earth, he said.
Tsunamis are a series of large, hazardous ocean waves caused by earthquakes or volcanic eruptions under the sea. Tsunami waves strike with devastating force and can quickly flood low-lying areas.
Tsunami waves may keep hurtling toward land for hours — from as little as 10 minutes apart to as long as an hour apart.
Cheung said some challenges in translating models into maps is that they don’t always land squarely where a road ends. The extreme evacuation maps are created with additional buffer zones, using highways and roadways as boundary markers.
Computer models, however, are only approximations of nature, according to Cheung, so there are always uncertainties.
“The yellow zone is for something we don’t expect to occur or something with very low probability,” said Cheung. “But if it happens we are prepared — we know how far inland people need to evacuate.”
Honolulu County added the yellow zones to its evacuation maps in 2015, and shortly afterward, Kauai, Maui and Hawaii counties followed.
UH recently created an educational video about the difference between a tsunami watch and warning, and the red and yellow zones.
A tsunami warning
When a tsunami warning for Hawaii was issued just before 2:45 p.m. on July 29, the estimated arrival of the first tsunami wave was 7:17 p.m.
The Pacific Tsunami Warning Center determined wave heights across the isles ranged from 0.4 to 5.7 feet. Some flooding occurred in Hilo and Hanalei, but no significant damage was reported.
What some evacuees recalled the most was the traffic gridlock, especially in dense, urban areas like downtown and Waikiki.
There is no official count of how many people from yellow zones — or even green zones — moved to higher ground during the warning. Collins said, “Some people knew, and others didn’t.”
As for tourists, most were likely unaware of the different tsunami evacuation zones.
“We work with the Hawai‘i Visitors and Convention Bureau to get hazard information to hotels and our tourism industry partners,” he said. “That includes tsunami zones and what to do during a warning. Hotels are responsible for having plans and helping their guests evacuate if needed.”
Now that the warning has passed, he hopes residents will prepare ahead of time.
“Knowing which zone you’re in should be part of every personal and family preparedness plan,” he said. “We’re committed to making the message clearer, and we hope the community stays engaged and informed.”
Another lesson learned, he said, is that many did not consider vertical evacuation, which added to the gridlock.
“Being above the fourth floor in a sturdy building is just as effective as evacuating out of the zone,” he said. “In future warnings, we want people to think about all safe options — upward and inward. Vertical evacuation saves time and reduces congestion.”
Nevertheless, he said, “If even one family was confused during the warning, that tells us we have more work to do. We are always looking at ways to improve how we communicate the evacuation zones, but it’s also important for everyone to know their zone before the next warning.”
Maps have evolved
Hawaii was the first U.S. state to implement tsunami evacuation maps for emergency response operations in 1963.
Those maps only included red zones, and were based on run-up observed from the four most destructive tsunamis in the prior 142 years of history.
According to Cheung, before then, in the 1950s, all people living in coastal areas less than 50 feet above sea level were to evacuate during a tsunami warning.
This was based on the 50-foot run-up, the largest, observed during the 1946 Aleutian tsunami. But officials realized they evacuated too many people, without accounting for variations.
In following decades, scientists were able to be more precise due to additional data and new technologies.
In 1991, evacuation maps were revised using 1D modeling of observed run-up from the five most destructive tsunamis in history, including the 1963 Alaska tsunami. Between 2011 and 2013, officials revised the maps using updated topography from LiDAR surveys and 2D modeling. In 2015, the extreme evacuation zones were added.
Historically, Cheung said locations most affected by tsunamis include Hilo, Kahului, Haleiwa, and Hanalei.
“Those locations always see big waves primarily because the sea floor geometry has a tendency to amplify the waves at those locations,” he said.
Honolulu County officials in recent years installed tsunami hazard signs at roads and coastal parks across Oahu, with a QR code that links to tsunami evacuation maps. Signs at beach parks are in red zones, while those along roads mark the edge of extreme evacuation zones.
An extreme tsunami event could happen once in 1,000 years, but with climate change resulting in higher sea levels, scientists and officials say it’s always better to be prepared and to be safe rather than sorry.
IN THE ZONE
Know your evacuation area
>> Tier 1, red zone, tsunami evacuation zone.
>> Tier 2, yellow zone, extreme evacuation zone.
>> Green zone. Safe zone.
Where to find your zone
>> The maps are listed on multiple sites via HI-EMA, county websites and National Oceanic and Atmospheric Administration.
>> Quick list of zones on all islands: static.pdc.org/tsunami/index.html.
>> For Oahu: Go to honolulu.gov/tsunamievac for interactive map (allows you to enter an address to learn which zone you are in).
>> Learn more about tsunamis at honolulu.gov/dem/tsunami.
>> If you don’t have internet access, look for the “Disaster Preparedness Guide” in your phone book. The Hawaiian Telcom phone book offers the guide in the front section, but the maps are not in color as they are online.
THINGS TO KNOW
>> A tsunami can occur any time of day or night. Know evacuation zones (for home, work and school) ahead of time, and plan your evacuation.
>> There are four levels of tsunami alerts: warning, advisory, watch and information statement.
>> During a tsunami warning, traffic could cause delays, so plan to walk to a safe location if possible.
>> Consider vertical evacuation. Proceed to the fourth floor or higher of a building that is 10 stories are taller.
>> If not located in a tsunami evacuation zone during a warning, stay home and off the road.
>> Remain at least 100 feet away from inland waterways, marinas connected to the ocean due to wave surges and possible flooding.
>> Local tsunamis (from an earthquake on Hawaii island, for example) are different. If you feel an earthquake, hear a loud roar from the ocean or water drains suddenly, a tsunami could arrive within minutes. Move to higher ground immediately (don’t wait for official guidance).
Source: Honolulu Department of Emergency Management, Hawaii Emergency Management Agency
Source: The Garden Island
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