Travertine is a form of limestone deposited by mineral springs, especially hot springs. Travertine often has a fibrous or concentric appearance and exists in white, tan, cream-colored, and even rusty varieties. A travertine terrace is formed when geothermally heated alkaline waters emerge to the surface and form waterfalls of precipitated carbonates.
Krka National Park in Croatia
By Version13 at English Wikipedia – Transferred from en.wikipedia to Commons., Public Domain, Link
Hierve el agua, Oaxaca, Mexico
Image by Carlos Adampol
Badab-e Surt, Mazandaran, Iran
M. Samaee (M. Samaee’s gallery) [CC BY 3.0], via Wikimedia Commons
Waterfalls Hierve el Agua
Image by Eduardo Robles
Fly Geyser, near Gerlach, Nevada
Image by Ken Lund
Dead trees in the terraces of Mammoth Hot Springs, Yellowstone National Park
By Brocken Inaglory (Own work) [CC BY-SA 3.0 or GFDL], via Wikimedia Commons
Aerial view of pools, Huanglong, Sichuan, China
By chensiyuan (Own work) [GFDL or CC BY-SA 4.0-3.0-2.5-2.0-1.0], via Wikimedia Commons
e MORFES 
stunning!
They all have the WOW ! factor !
Beautiful.
Immagini uniche e di straordinaria bellezza. che è un piacere apprezzare!
Buona serata e un saluto,silvia