A lahar is a type of natural disaster closely related to a volcanic eruption, and involves a large amount of material originating from an eruption of a glaciated volcano, including mud from the melted ice, rock, and ash sliding down the side of the volcano at a rapid pace.
The town sits in a fertile valley between two major rivers, the Carbon and Puyallup Rivers, and it is built entirely on several layers of lahar deposits.
In 1778 Hamilton was promoted to lieutenant and in 1780 was once again in action during the First Anglo-Maratha War, where his troops participated in the storm and capture of Lahar, Gwalior and Bijaigarh from the Maratha Empire.
On 5 April 1982, the volcano of Gunung Galunggung erupted about 24 km from the city, causing major damage through lahar and ash projection, and forcing a temporary evacuation of the area.
The Spanish conquistadors also called it Hunapú until a lahar from the volcano in 1541 destroyed the original capital of Guatemala (now known as Ciudad Vieja) and the city was moved to the current site of Antigua Guatemala following this disaster.