Hi Barry - lots of things can cause noise on the webicorders.. wind, rain, snow - weather related items...

From the PNSN site: Other interesting signals may be recorded. For example rockfalls (see a station near Mount St Helens), icequakes in glaciers (see station RCS), ground motion induced by high wind conditions or man-made blasts (for example, the quarry blasts near Centralia, WA each day).

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