Lahars are a specific kind of mudflow made up of volcanic debris. They can form in a number of situations: when small slope collapses gather water on their way down a volcano, through rapid melting of snow and ice during an eruption, from heavy rainfall on loose volcanic debris, when a volcano erupts through a crater lake, or when a crater lake drains because of overflow or wall collapse.
A relay is an electromagnetic switch operated by a relatively small electric current that can turn on or off a much larger electric current. The heart of a relay is an electromagnet (a coil of wire that becomes a temporary magnet when electricity flows through it).
There are two relays in the flasher unit. I call them the master and the secondary relays. Here is a functional schematic of the flasher unit. When the turn signal is activated with the right hand side thumb switch the transistorized timer circuit in the flasher applies a pulsating signal to the master relay coil. This sends a current through the secondary relay coil as well as lighting up the signal lights on the motorcycle.