import folium
import pandas

df=pandas.read_csv("Volcanoes-USA.txt")

map = folium.Map(location=[df['LAT'].mean(), df['LON'].mean()], zoom_start=6, tiles='Stamen Terrain')

def color(elev):
    minimuum=int(min(df['ELEV']))
    step=int((max(df['ELEV'])-min(df['ELEV']))/3)

    if elev in range(minimuum,minimuum+step):
        col='green'
    elif elev in range(minimuum+step,minimuum+step*2):
        col='orange'
    else:
        col='red'
    return col

for lat,lon,name,elev in zip(df['LAT'],df['LON'],df['NAME'],df['ELEV']):
    map.add_child(folium.Marker(location=[lat,lon],popup=name,icon=folium.Icon(color(elev),icon_color='grey')))

map.save(outfile='test1.html')