1. Galvanic corrosion occurred when copper (Cu) and lead (Pb) metals were in contact where they were attached on the roof of Sampson Hall. 2. When dissimilar metals like Cu and Pb are in contact in the presence of an electrolyte like water (H2O), an electrochemical reaction occurs between them. 3. In the galvanic series, Cu is more noble than Pb, so the Pb acted as the anode and corroded as electrons flowed from it to the Cu cathode. This caused leaks to form from the breakdown of the Pb material