3,000 people in 3 coastal towns locked down in La Palma after new lava flow crashes into ocean forming new delta

admin / November 23, 2021 / Volcano, Volcano erupts

Authorities on the Spanish island of La Palma ordered 3,000 residents of three coastal towns (​​Tazacorte, San Borondón, El Cardónto) stay indoors on Monday after a new stream of lava crashed into the ocean, sending thick clouds of potentially toxic gases high into the sky.

A third tongue of lava from the Cumbre Vieja volcano, which has been erupting for two months, reached the water around midday (12:00 GMT) a few kilometres north of where two previous flows hit the sea.

Drone footage from the local council showed white clouds billowing out of the water as the red hot molten rock (up to 1000°C) slid down a cliff into the Atlantic (20°C).

Residents in Tazacorte, San Borondon and parts of El Cardon were told to stay inside with doors and windows shut as strong winds blew the cloud back inland.

Soldiers from the Military Emergency Unit were deployed to measure air quality in the area while lava flow is speeding up…

Meanwhile, lava flows 4 and 7 have ‘united’ into a larger stream in the mountains near Todoque and La Laguna covering an extra eight hectares…

The larger delta is now 43 hectares. Amazing growth since Sept. 28th, no?

Ocean entry hazards

Getting too close to an ocean entry, either on land or from the sea, is potentially deadly. Primary hazards include:

  1. Sudden collapse of a lava delta (new land created at ocean entry) and the adjacent sea cliff into the ocean.
  2. Large explosions triggered by delta collapse.
  3. Waves of scalding hot water from ocean swells and delta collapse.
  4. Steam plumes that rain hydrochloric acid and tiny volcanic glass particles downwind from the entry point.

Visitors to an active ocean entry should pay attention to warning signs that may be posted in the area.

Scientists cannot predict the timing or size of a lava delta collapse. They also cannot predict which direction and how far fragments of lava and rock will be hurled on land or seaward during a collapse-triggered explosion.

The best way to avoid these hazards is to never walk onto an active lava delta and maintain a safe distance from a delta’s leading edge, even when on a boat. Once a new lava delta extends more than a few tens of meters (yards) from the old sea cliff, visitors should stay at least 300 m (330 yd) away from where lavais entering the ocean.

This is the maximum distance rocks and spatter have been thrown inland from the older sea cliff during past ocean-entry explosions. Small rock fragments can fall far beyond this distance.

1. Lava deltas collapse without warning

Lava entering the ocean builds a delta on top of unstable lava fragments along the steep submarine slope. As the delta grows seaward and laterally along the shoreline, it may slowly settle or sink as the loose rock debris shifts under the weight of overlying lava flows.

This subsidence may allow seawater to get into the lava tube system, which can generate lava bubble bursts and rare littoral lava fountains.

All or part of the delta can collapse into the ocean when the underlying debris can no longer support the delta’s growing mass or is undercut by a deeper submarine landslide. The collapses occur suddenly or over a period of several hours.

2. Explosions often triggered by delta collapse

Lava entering the ocean generates different types of explosive interactions with seawater. The largest and most dangerous type of explosion is triggered by a delta collapse.

The sudden mixing of seawater, hot rocks, and lava with temperatures about 1,150 degrees Celsius (2,100 degrees Fahrenheit) may cause steam-driven explosions from the collapsed area.

Such explosions have hurled hot rocks nearly a meter (yard) in size as far as about 250 m (273 yards) inland from the collapsed delta and scattered rock debris onshore over an area the size of several football fields.

These explosions also hurl rocks seaward, probably to similar distances.

3. Waves generated by delta collapse heated to scalding temperatures

Large portions of an active lava delta are extremely hot because of lava flows on its surface, lava tubes beneath the surface, and still-hot solidified flows throughout a delta.

A larger than usual ocean wave that sweeps across the surface of a hot delta can quickly reach scalding temperatures. People standing near lava deltas have received second-degree burns from such hot waves and accompanying steam.

Delta collapses can also produce waves both onshore and offshore, which can imperil boats next to a collapsing delta.

4. Ocean-entry plume is acidic

A white plume on the edge of an active lava delta marks where lava meets seawater – this plume can cause skin and eye irritation and breathing difficulties and should be avoided.

As hot lava boils cool seawater, a series of chemical and physical reactions create a mixture of condensed, acidic steam, hydrochloric acid gas, and tiny shards of volcanic glass. Blown by wind, this plume creates a noticeable downwind haze, known as “laze” (short for lava haze).

During prevailing trade-wind conditions, which exist more than about 80 percent of the time, air flow from mid-morning through late afternoon carries the plume onshore and along the coast. This can cause poor air quality for people downwind of the ocean entry. From nighttime through early morning, trade-wind flow typically blows the laze off shore and out to sea. [Reuters, USGS]

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