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).
Impulse relays are a form of latching relay that transfers the contacts with each pulse. Many impulse relays are made up of a. magnetic latch relay and a solid state steering circuit that, upon application of power, determines which position the relay is. in and energizes the opposite coil. The contacts transfer and hold that position when power is removed.