Mount Hood's last major eruption occurred in the 1790's not long before Lewis and Clark's expedition to the Pacific Northwest. In the mid-1800's, local residents reported minor explosive activity, but since that time the volcano has been quiet.
Signal Colors and Their Meaning. The colors used in today's signals are green, yellow, red, lunar, and white (remember, we're talking about signals in North America). The color of a signal tells the engineer what he has to do, the location of that color, determines the speed at which he is allowed to do it.We will get to the speed thing in a minute.he colors used in today's signals are green, yellow, red, lunar, and white (remember, we're talking about signals in North America). The color of a signal tells the engineer what he has to do, the location of that color, determines the speed at which he is allowed to do it. We will get to the speed thing in a minute.
On the chart the yellow color indicates a very strong signal, the green indicates a medium strength signal and the blue shows a weak signal. In part C of the signal there is a continuous tone at 2100 Hz which remains during the whole pulse and sometimes several seconds afterward. There is also a much weaker tone around 2500 Hz during all of the pulse.