Posted on

Observations for 2021 September 04


Thw walkway past Rift had a nice coating of frost in the morning, as did the benches. It got heavier as I waited through the Turban intervals after a long Turban Delay Interval. It wasn't warming up as there was a thin layer of clouds that had replaced the smoke. But the One Burst Grand was nicely visible as the steam was being pushed to the south.

Toward noon, I decided that checking on Fan & Mortar was a good place to waste some time. Over 45 minutes I saw what appeared to be "garbage mode", where the Fan vents come and go, look good at first, but there's never any prolonged gap or activity from Mortar. So decided that I should check on East Sentinel, then head in.

As I approached, I saw a larger than usual steam cloud from East Sentinel. It appeared that I was seeing the activity between minor eruptions. The vent was empty as I arrived, while there was some jetting from the south rim toward the north inside the vent itself. There was steam coming from the small vents to the south of the crater.

Empty crater of East Sentinel

Over the next few minutes the activity of the vents picked up, leading to a small minor eruption from an empty crater. About ten minutes later there was a second such increase in activity.

Then water became visible at the bottom of the vent, rising quickly. It got as high as about 1-1/2 meters from overflow, then started fluctuating. Around this time thumping could be heard. The pool finally rose to about 1/2 meter below overflow, when the activity shifted from the south to the north.

Now some horizontal jetting could be seen well under the shelf. The small vents to the south had stopped steaming by this point. After a while with no change, left the area on the assumption that it was in a refilling mode.

From there it was time for Grand, and another One Burst Eruption. That was immediately followed by the start of Beehive's Indicator, so a quick trip to Geyser Hill was in order.

A few hours later I decided to check on East Sentinel and Fan & Mortar again. I arrived at East Sentinel to find that the activity had shifted again, with the south rim boiling vigorously. Over the next few minutes, the water level in the crater rose as the activity increased. Water was pouring out of the runoff slot, while the south vents were jetting a couple of meters in height, including some horizontal activity to the east (the mostly dry channel at the front).

This activity lasted about three to four minutes, then the water level dropped and the boiling subsided. Over the next hour, the water level would rise to overflow, then drop. Eventually the overflow was so heavy that the runoff notch couldn't contain it, and water started running south over a low spot in the rim. At that point, surging started again, and we got another eruption, stronger than the previous. This one lasted under three minutes, and once again the crater water level dropped about 30cm at the end.

East Sentinel minor eruption

Following this the rising and falling started again, but I decided that it would be nearing dark before the next attempt, and left.

Did go out for the after sunset One Burst Grand eruption. This one lasted over twelve minutes, and featured a couple of false pauses, one at around the 8-1/2 minute mark, the other a few seconds before Grand finally quit.