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From the level of Minerva Terrace stairs climb up to the level of Main Terrace and beyond, where the trail runs along the elevated, eastern rim of a travertine terrace called The Esplanade. It is named for the panoramic view over Main-, Jupiter- and Mound Terrace and continues (without trail) northwestward to tower over Minerva Terrace, too. The Esplanade has no historical record of flowing thermal water and is regarded as part of Prospect Terrace, the next higher level on Terrace Mountain. Looking down on the lower terraces' northwest corner, pools and terracettes of New Blue Spring catch the eye.
Actually, New Blue Spring consists of several different vents, and the position of the pool shifts from time to time accordingly. The original Blue Spring, described by the Hayden expedition in 1872, was located more or less at the same position of the current New Blue Springs. But the original one ceased flowing in 1889, and another spring near the center of Main Terrace was named Blue Spring instead. Later springs at the former position sprang into life and they were called New Blue Springs. Up until 2005 New Blue Spring flowed high volumes of thermal water, cascading down the brink and continuously forming or extending terracettes. But thereafter the discharge dropped and the water has been confined to some smaller pools on top level only. The next picture shows a spring located near the boundary to Jupiter Terrace. In most years this spring is empty.
Southwest of the New Blue Springs one of the dry vents of Summit Basin Spring is still visible. This spring had ceased flowing in 1872 and became a top attraction when its two large pools refilled in 1936. In his New Guide from 1936 Jack E. Haynes wrote: "Jupiter Terrace Parking Area (Mileage 6.5) affords a splendid view of Summit Basin Spring." However, the excitement was short-lived because the spring already dried up again at the end of 1937. Although at that time the name Summit Basin Spring had been officially used in the superintendents' reports, the sign at the current overlook directly in front of the old vent, reading "New Blue Spring", seems to allocate it now to the New Blue Springs.
The boardwalk proceeds along The Esplanade and passes Cupid Spring, which is likewise part of the higher Prospect Terrace. Cupid Spring was firstly observed in 1931 and its last noteworthy period of activity ceased in the 1990s. From 2010 onwards, Cupid Spring showed new discharge, which is getting stronger from year to year.
South of Cupid Spring the old boardwalk (up until 2014) curved east around Trail Spring. Located at the southwest corner of Main Terrace, it came into existence in 1962 and has been intermittently active since then. As already seen before with other springs, over the time different vents may emerge. The vents, which were active from 2007 to 2013, are called New Trail Spring.
The contrast between the petrified ground and interspersed tree skeletons is the signature feature of New Trail Spring.
2013 was the most recent year so far when New Trail Spring displayed water.
Across the old boardwalk from New Trail Spring, Grassy Spring has developed a remarkable travertine bed since it has emerged in 2008. Eventually, in 2014, the boardwalk had to be shifted to the west upslope of Grassy Spring's vent to prevent any interference with the natural travertine deposition process.
As a newly emerged spring literally on a green field, Grassy Spring impressively illustrates the process of terrace formation from the earliest stages on. Starting from the currently existing micro terracettes, the rising new terrace will develop terracettes with successively deeper ponds, and on the long term overhanging terracette deposits, if activity continues long enough.
The new boardwalk above Grassy Spring also passes a cavity, which was almost completely obscured before. This is an example of a solution cave (a cave eroded by cooled down spring water or rainwater) in the limestone of Mammoth Hot Springs, but it is only a small one. Larger caves, such as the Stygian Caves (encompassing Stygian Cave, Stalactic Cave and Hermit’s Cave), Poison Cave, and the Devil's Kitchen are located in the Upper Terraces Area, while McCartney's Cave is to be found on Hotel Terrace. To none of the caves access is permitted any longer, not even to the area of their entrance. The Devil's Kitchen had been open to visitors until 1939, but then it was closed due to an unpredictably changing carbon dioxide concentration in the air and lack of oxygen. Repeatedly, huge numbers of animals, mostly birds, were found dead inside the caves due to poisoning by carbon dioxide.
Dryad Spring, a short distance farther east, underwent a similar development over nearly the same period of time as Grassy Spring. The spring's first vent came to existence inside a small patch of trees and therefore was named after a dryad, a tree nymph in Greek mythology.
Since the 1870s Canary Spring, named after its canary bird yellow color, has been intermittently active and often was one of the stars of Mammoth Hot Springs. Its water formed beautiful terracettes on Marble Terrace, the steep slope at the southeast corner of Main Terrace. Unfortunately, as had been observed several times in the past, since 2012 the discharge of Canary Spring once again has declined dramatically.
In 2013 the pool of Canary Spring shrunk to small ponds around the vent, and the runoff over the brink of Main Terrace ceased. During the same time a spring farther north, beyond Canary Spring, has amplified its activity considerably. In the strict sense this waterbody is fed by vents in the perimeter of the Main Springs. However, the entrenched name Canary Spring persisted, not least because of the sign attached to the handrail.
It seems as if the activity of the "old" Canary Spring shifted northwards. There, a series of widely protruding, awesome terracettes rose in a short time. The disadvantage for visitors is, however, that the spectacle takes place at a distinctly larger distance to the boardwalk compared to the old Canary runoff.
After the thermal water has dropped over the brink it cascades down the slope and builds up terracettes which resemble open, filled barrels. This east slope of Main Terrace is called Marble Terrace.
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