A Week At The OVT: Day 4

For most of the people around Banos, today marks the beginning of a holiday. A Hallowe’en Saturday, Sunday, Monday holiday, Tuesday Dia de los Muertes; all together, what a pleasure! To us at the OVT, we’re at work. For me, I don’t see lights or sound or colour. This post is about mud, and murk, and mystery.

Today is Saturday, October 31st. Yesterday, our early morning sunshine had darkened into cloud by the early afternoon, and from our house in the valley we saw grey clouds pass us by. Nevertheless, there was no rain upon the mountain. We saw none, and our omniscient instruments agreed. And yet two of our vigias told us they had seen a lahar on the mountain, crossing their paths with some speed, a racing stripe on the mountain. Where did it start? This unidentified flowing object could have no source that we could think of; there was no rain on the mountain, and we’d seen dust bowls blowing off the hills the last two evenings past.

Back to today. In the late morning, we travelled to the quarry where the lahar had been observed. It was there, all right. A vivid orange-brown mud, a paint bucket dropped on the quebrada floor, who knows from where. When we touched it the mud coated our fingers like tempered chocolate. The base of the stream offered a fine view up the valley; we would be able to walk up the streambed and find the source, provided it did not rain overnight.

UFO turns out to be lahar. Here’s the one the mountain made earlier.
Appearance of active flow (foreground) and its finale (background).

Now, as fascinating and visceral as the topic of viscous mud is, that’s where I have to leave the story. We have decided to discover the source of the UFO tomorrow morning instead. Nevertheless, in this active country we live in, there’s usually something else to take its place. I present to you:

DRUMBEAT SEISMICITY AT TUNGURAHUA VOLCANO

As seen and described by Patricio Ramon, and to me by Liz. The stages are:

1. Two to three days of ash emissions, accompanied by emission tremors on seismograph (long signals, moderate amplitude of continuous size). This corresponds to the beginning of the OVT week, when we observed ash plumes rising from Tungurahua on Wednesday.
2. A day or two involving decrease in activity, with emission tremors decreasing in amplitude.
3. A short period displaying occasional long-period (LP) activity, perhaps 12 hours. In this period, the LP events appear as small-amplitude screw-shaped signals on the seismograph, with an event lasting under a minute and appearing every few hours.
4. A period of increasing activity with regular LP events forming a ‘drumbeat’. One every minute or so (look for the tiny kink band on the seismograph, each one defines a new minute). Drumbeat seismicity is so-called because of the regularity of the events.
5. New Eruption or Emission!

Seismograph, mid-afternoon. 
In detail, late afternoon: large teleseismic event occurs before
swarm of small, regular long-period (LP) events.

Also seen here – two large teleseismic events today (larger amplitude, long-distance, single events). I hope we’ll see a new emission tonight; if it’s clear, we may see some incandescence later (we are currently at 18:17pm).

DB seismicity caused by either viscous plug movement or escape of gases from magma-conduit boundary? (Mario Ruiz). Second hypothesis never heard of by Liz for lasting for such a long time; but apparently recorded at Montserrat.

NB! Drumbeat seismicity is formed by a repetitive, non-destructive source (see notebook). It usually suggests dome formation, as at Mount St. Hekens in 2004 and 2008; the drum beats illustrate movement upwards in the conduit of highly crystalline magma. The IG’s soot seimograph is useful for on-the-dot info, rather than longer-term monitoring. Dome formation would be disastrous for Tungu, because dome formation, and its eventual collapse, would form larger pyroclastic flows. The extremely steep flanks of Tungu would channel these flows into vulnerable, populated areas. However, dome formation may not be conclusively proven from drumbeat seismicity.

For all the science that I’ve just spewed, there’s nothing like the visceral thrill you get from waiting for a volcanic eruption. I spent an hour in the OVT’s main room, breathless, waiting for Step 4 to transition into Step 5. Outside in the valley, the light changed from pink to grey; and I stood there, waiting, waiting for Tungurahua to blow.

We spend the evening in Banos. On the streets there were so many people. Young, old, strangers, locals. A busker passes us by; he is going to make a killing tonight, because it’s the first night of the long weekend, that ends on Dia de Los Muertos, or All Souls’ Day, this Tuesday 3rd November. All the others are out for a party, but I am otherwise preoccupied, still thinking about the muddy water we’d seen earlier. Pretty sad, you might say. Or, you’ve got a filthy mind! Only half-right. This is a fantastic mystery. I’m pretty sure I know where most people would end up tomorrow – in their bed or someone else’s, possibly feeling pretty hungover. I’m not judging. I’ve done that plenty of times before, and I will definitely do it again. But of all the people on the streets of Banos, they know where they’re going to end up tomorrow morning. I don’t, and that is what geology has given me. Tomorrow we’re going on a microadventure, to find the source of the orange thread.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s