How to Survive a Landslide-Generated Megatsunami: Lessons from the 2025 Tracy Arm Event

On August 10, 2025, a colossal landslide in Alaska's Tracy Arm fjord sent a 100-meter-high wave racing across the water at over 70 meters per second. The wave surged up the opposite shore to 481 meters—the second highest tsunami ever recorded. Remarkably, no one was killed or injured, largely because the event struck at 5:26 a.m. local time when few were present. But landslide megatsunamis are becoming more frequent as mountain slopes destabilize, and we may not be so lucky next time. This guide explains how such tsunamis form, what warning signs to watch for, and how you can stay safe if you're in a high-risk area like a narrow fjord.

What You Need

• Knowledge of local geography: Know whether you are in a narrow fjord, lake, or reservoir prone to landslides.
• A reliable communication device: Satellite phone, marine radio, or charged cell phone with emergency contacts.
• Emergency evacuation plan: Identify high ground routes at least 50 meters above sea level, but ideally 500 meters or more for extreme events.
• Weather and seismic monitoring apps: Services like USGS earthquake alerts or local landslide warnings.
• Basic survival kit: First aid, extra clothing, food, water, and a flashlight—ever useful after a sudden evacuation.

Step-by-Step Guide

1. Step 1: Understand the Risk Factors for Landslide Megatsunamis

   Landslide tsunamis are far more violent than earthquake-driven ones. While earthquake tsunamis typically have runup heights of just a few tens of meters, landslide megatsunamis can exceed 500 meters. The Tracy Arm event involved 63.5 million cubic meters of rock detaching from a mountain above the fjord—a volume equivalent to about 25,000 Olympic swimming pools. When such a mass falls into a narrow, deep water body like a fjord, it displaces water so suddenly that towering waves form. Since 1925, scientists have recorded 27 landslide tsunamis with runups over 50 meters; the largest was the 1958 Lituya Bay tsunami at 530 meters. Knowing that you are in a geographical setting where steep slopes overlook confined waters is the first step to staying alert.

   

2. Step 2: Recognize Pre-Eruption Warning Signs

   Landslides rarely occur without some precursors. Look for fresh cracks on mountainsides, unusual rockfalls, or changes in water color near glacier termini (e.g., increased sediment). In the Tracy Arm case, the wedge of rock detached suddenly, but many large landslides are preceded by smaller failures, seismic tremors, or audible rumbling. If you hear a loud roar or feel ground vibration near a fjord, do not wait—move to higher ground immediately. Also monitor official alerts: geological surveys often issue warnings for known unstable slopes.

3. Step 3: Evacuate Immediately When Tsunami Is Imminent

   If you see a massive rockfall into water, or if local authorities broadcast a warning, evacuate at once. Do not stop to take photos or wait for confirmation. The Tracy Arm wave traveled at >70 m/s (156 mph)—far faster than any person can run or any boat can outrace. Head straight for high ground: ideally at least 500 meters above sea level if you're near the impact zone. Because the wave can surge up steep slopes (as seen with the 481-meter runup), distance from the shoreline is not enough; you need elevation. If you are on a boat, steer away from the fjord walls and toward the open ocean as quickly as possible, but be aware that waves can also rebound off walls. If no high ground is reachable, climb onto a sturdy structure or tree as high as you can, though this is a last resort.

   

4. Step 4: Survive the Wave Impact and Aftermath

   If caught in the wave, try to stay afloat, protect your head, and avoid debris. Once the initial surge passes, be aware that multiple waves may follow, and backwash can drag you out to sea. Wait for official all-clear signals before returning to low-lying areas. The Tracy Arm event happened early morning, minimizing exposure; but if you survive, check for injuries, help others if safe, and report your location via satellite or radio. Post-tsunami hazards include unstable slopes that may collapse again, so avoid the base of mountains until a geologist deems them safe.

5. Step 5: Learn from Historical Events to Prepare Better

   Study documented landslide tsunamis to understand patterns. The Tracy Arm event was a near-miss, but it highlights that such catastrophes can strike even remote tourist areas. If you live or travel in similar settings (Alaska, Norway, New Zealand, British Columbia, Patagonia), develop a personal emergency plan, keep a bug-out bag, and practice evacuation routes. Encourage local authorities to install warning systems—such as seismic sensors or sirens—that can give minutes of lead time. The more you know, the less likely you become a statistic.

Tips for Maximizing Safety

• Never assume you are safe just because no tsunami has occurred in recent memory. Landslide frequency is increasing due to glacier retreat and permafrost thaw.
• Use the “10-second rule”: If you see a rockfall into water, you have about 10 seconds before the wave reaches the opposite shore in a narrow fjord. That is not enough time—so be pre-positioned on high ground.
• Travel in groups and brief everyone on the escape plan before heading into fjord areas.
• Invest in a personal locator beacon (PLB) that works even when cell networks are down.
• Remember the Lituya Bay lesson: that 1958 wave wiped out all vegetation up to 530 meters. If you see a bare slope high above the water, it may have been stripped by a previous tsunami—indicating the potential for another.
• Stay informed via the What You Need section for tools that can alert you.

By understanding the science and staying vigilant, you can dramatically increase your odds of surviving a landslide megatsunami—even one as powerful as the 2025 Tracy Arm event.