This article was published on: 03/15/24 3:15 PM
This just in: Central Oregon has been in drought — for a while.
Yet, in May of 2022, we were at 106% of our average snow-to-water equivalent. In May of 2023, we were at 169%. And as of March 1 of this year, we are at 112%.
So why is it that most of Central Oregon is still abnormally dry or in moderate drought? Because Central Oregon, is basically a giant sponge.
Central Oregon is still somewhat volcanically active, which means we end up with a lot of porous, permeable rocks as opposed to the older, more weathered rocks on the west side of the Cascades.
“So, when rain or snow falls on the western side of the Cascades, it doesn’t soak into the ground,” said Prof. Daniele McKay, Earth Sciences instructor at the University of Oregon. “It might soak in a little bit. The soil can hold some water, but most of that water is going to run across the surface as rivers or streams.”
McKay tells me the best way to visualize how Central Oregon is like a sponge is — with a sponge.
“I know people who live in Central Oregon are familiar with basalt and it’s hard to think of basalt as being similar to a sponge. Basalt is very dense, solid rock. It’s the reason most of us here in Central Oregon don’t have basements because it’s really expensive to excavate through this stuff,” McKay said.
Basalt is filled with tiny little holes just like a sponge. So when the rain or snow falls onto the basalt lava flows, it retains water — just like when you pour water into a sponge.
“And so we can pour water into the sponge, or on the sponge, which is our lava flow, and none of it is flowing across the surface as a river,” McKay said.
Now, here’s something that I didn’t know. You’d think in a land with so many underground lava tubes, they would serve as a perfect straw for the sponge and speed the delivery of water downhill, right?
Wrong.
“So, often times there is a misconception that the groundwater must be flowing through lava tubes,” McKay said. But she points out that because of the sponge effect, the water soaks through and drips down to the floor of the lava tube. “And it comes out with all the rest of the groundwater as springs.”
The spongelike basalt soaks up a lot of water. Thus, it can continue to feed water into our springs for years without much precipitation at all.
“So you can have dry years for many years. And depending on the length of time that this water travels through the sponge, the spring here won’t know that you’re in drought because it’s just still getting all of that water that that sponge was holding from decades prior,” McKay said.
But much like what is happening now, that feature is a bit of a double edged sword.
“And then it’s similar when you get to several wet years. Then there’s more precipitation,” McKay said. “But a lot of that water is just going to refill the sponge and we’re not going to see the effect in the springs. It’s not like we have a heavy snow year and all of the sudden those springs are just gushing. So the sponge acts kind of like a buffer. It protects us from drought, but it also means that when we’ve had multiple drought years, we’re going to need more time to recharge that system.”
And that system is so big and so deep, that in theory, water we are drinking today could be water that fell when John Fremont, Kit Carson and Billy Chinook first came through Central Oregon.
“Yep. We don’t know the exact age of that water, but we do know that it is at least, you know, 50, 60, 70 years old, maybe much older,” McKay said.
(Correction: We incorrectly identified McKay as working for Oregon State University in a previous version of this story.)