Formation and Composition

Cold lava forms when rainwater mixes with volcanic materials such as ash, sand, and pebbles ejected during volcanic eruptions. This mixture creates a dense, concrete-like slurry that can flow downhill rapidly.

Destructive Potential

Unlike traditional lava flows, which move slowly and typically allow for evacuation, cold lava can advance swiftly at speeds reaching hundreds of kilometres per hour. This rapid movement is due to the high water content in the lahar, enabling it to travel far distances—up to 60 kilometres from the volcano.

Volume and Spread

Cold lava can accumulate additional debris and sediment as it travels downhill, rapidly increasing its volume and destructive force. This makes it capable of causing extensive damage to buildings, infrastructure like bridges and roads, and posing a serious threat to human life.

Characteristics

Despite its name, cold lava remains internally hot due to chemical reactions within the volcanic material. Externally, it resembles wet concrete in its behaviour, flowing downhill and engulfing everything in its path.

Origin Without Eruption

While cold lava is commonly associated with volcanic eruptions, lahars can also occur without an eruption. Heavy rainfall or snowmelt can erode loose volcanic sediments, especially if the area lacks vegetation to stabilise the soil, resulting in the formation of lahars.

Comparative Destructiveness

Cold lava (lahar) is considered more destructive and deadlier compared to regular lava flows due to its rapid movement, high density, and abrasive nature. Its ability to transport large volumes of debris downhill makes it particularly hazardous to nearby communities.

PRACTICE QUESTION

Q. How many of the following factors contribute to the severity of a lahar?

1. Steep terrain

2. Proximity to rivers

3. Previous rainfall patterns

4. Lava flow characteristics

Select the correct answer using the codes given below:

A) Only one

B) Only two

C) Only three

D) All four

Answer:  C