Volcanic Steam When Lava Meets Ocean: A Hidden Health Hazard Called “Laze”

Most people think of glowing red rivers of lava or explosive ash clouds when they picture a volcanic eruption. But in coastal volcanoes like Kīlauea in Hawaiʻi or the ongoing eruptions in Iceland’s Reykjanes Peninsula, one of the most immediate public health threats isn’t the lava itself; it’s the white plume that billows up where 2,000 °F (1,100 °C) molten rock slams into cold seawater.

That plume is called laze — a word formed from “lava” + “haze” — and it is far more dangerous than it looks.

#### What Exactly Is Laze?

When lava instantly boils seawater, two dangerous things happen:

1. Hydrochloric acid (HCl) cloud  

   Seawater contains chloride salts. Superheated lava flashes the water into steam and reacts with those salts to produce concentrated hydrochloric acid vapor. Concentrations can reach levels similar to battery acid in the air.

2. Tiny shards of volcanic glass  

   The explosive shattering of lava creates microscopic particles of volcanic glass (similar to obsidian). These razor-sharp fragments are small enough to be inhaled deep into the lungs (PM2.5 and smaller).

The resulting plume can drift miles downwind depending on trade winds, sometimes even reaching residential areas or tourist viewpoints.

#### Health Effects of Laze Exposure

Short-term exposure (minutes to hours):

- Severe eye, nose, throat, and skin irritation

- Coughing, wheezing, shortness of breath

- Headaches and nausea

- In people with asthma, COPD, or heart disease, it can trigger acute attacks

Long-term or heavy exposure risks:

- Chemical pneumonitis (lung inflammation)

- Permanent lung scarring from glass particles

- Corneal burns or long-term vision damage

Fatalities directly attributed to laze are rare, but in the 2018 Kīlauea lower East Rift Zone eruption, several residents and visitors required hospitalization after inhaling laze plumes, and at least one death was linked to complications from laze exposure.

#### Who Is Most at Risk in 2025–2026?

- Residents living downwind of lava ocean entry points (e.g., Puna district, Hawaiʻi)

- Tourists taking boat tours or helicopter flights too close to active entries

- First responders and scientists monitoring the eruption

- People with pre-existing respiratory conditions, children, and the elderly

Current situation (as of December 2025):

- Hawaiʻi: No active ocean entry at Kīlauea right now, but the volcano remains restless.

- Iceland: The December 2025 Sundhnúkur series eruptions on the Reykjanes Peninsula are not currently producing laze (lava is flowing over land), but any future flow toward the ocean could change that quickly.

#### How to Protect Yourself If Laze Forms Near You

1. Stay upwind — Monitor wind direction in real time (apps like Windy or local Civil Defense updates).

2. Evacuate or shelter indoors with windows closed if plumes approach residential areas.

3. Wear an N95 or better respirator if you must be outside (regular cloth/surgical masks do NOT protect against HCl gas or glass particles).

4. Rinse eyes and skin immediately with clean water if exposed.

5. Never approach active lava ocean entries by boat or on foot — the U.S. Geological Survey and Hawaiʻi County enforce large exclusion zones for a reason.

#### The Bigger Picture: Climate, Volcanoes, and Public Health

As sea levels rise and coastal volcanic islands become more populated, the intersection of lava and ocean is likely to become more frequent. Better real-time air quality monitoring (such as the purpleair.com sensors now deployed around Kīlauea) and community alert systems will be critical for sustainable coexistence with active volcanoes.

Laze is a perfect example of how natural geological processes can create acute chemical hazards — and why respecting exclusion zones isn’t just about avoiding hot lava, but also invisible toxic steam.

Stay informed, stay upwind, and let the volcano do its thing from a safe distance.