Oct. 14, 2010 by Judy
The Great Advantage of Height
Speaking of the Galapagos (a couple of blogs back), how is it that they are so dry and we are so not? Cumulatively, I mean.
Hawaii’s rumpled green peaks and rounded humps heaving up from the cobalt sea are tall enough to divide and conquer the relatively steady tradewinds—Kauai, at about 5,000ft in elevation, is the nub of the Hawaiian island family but still tall enough to halt the waterladen winds and force them to drop what they’ve got on her flat summit. The bog up there is testament to that. Go and see. It’s cool. Literally, so bring a jacket. A rain jacket.
At the other end of the archipelago we’ve got the Big Kids--tall enough to be snowy between December and March. Shouldering up and through the cloud deck are Mauna Loa and Mauna Kea on the Big Island of Hawaii, each just under 14,000 ft. tall, and Haleakala here on Maui—10.023 ft tall and rising behind my backyard fence as I type.
What this mountainy impediment to the cross-Pacific airflow creates is called an orthographic rain pattern. In short, warm soggy air being blown across the ocean is pushed up against a mountain, is forced to rise and cool, and all that cloudy mist becomes heavy raindrops. If you are lucky enough to be spending time in Hana looking NE out to sea, your face is into those oncoming winds, and they will drop most of their rain up and behind you in the 4—7,000 foot altitude area. This smooshed-together wad of upwelling clouds banks and wraps around about a third of Haleakala’s slopes. Because you are facing into the wind here, you are on the windward side. If you are in Lahaina or Kihei, Makena or Kapalua, you are denied the rain by the bulk of the mountain between you and the rising sun direction (same as the tradewind direction, generally), and you are on the leeward side.
I think of water as a kind of relentless, patient sandpaper (hydropaper?) of sorts. Nothing can resist it, given enough time. Add in the gropings and pokings of plant roots and stone becomes soil, eventually. That windward side of the mountain is streaked and woven with streambeds, most of them in-flow for most of the year. They carve ever deeply into Haleakala’s flanks, and their heads work steadily upward as water crumbles the lips at the rims of the first waterfalls on the highest slopes. They sort of ‘eat’ their way uphill until they run out of uphill, or run out of rain to work with.
Imagine the amount of soil and rocks carried away since Haleakala first grew tall enough to encounter the cloud deck and grow through and even above it: tons and tons and tons and tons. Geologists theorize we have already lost about 4,000 ft. of summit in this way. The cloud deck snuggles around the mountain like a feather boa around a Broadway star, building most days quite predictably. The steady erosion of countless streambeds as well as the freezing/thawing cycle and the coming and going of winds will sand our big, big mountain down to sea level eventually. All tall mountains of Hawaii become atolls, then submerged seamounts, and then the movement of the Pacific plate pulls everything under Eurasia.
p.s.: What is commonly referred to as the ‘crater’ at the summit is actually the meeting of two massive water-carved valleys—Kaupo and Ko’olau—which approached the summit from opposite sides, met, and carried a lot of the summit away, down to the ocean. It’s called, unromantically but correctly, an ‘erosional valley’. The original round summit crater is long eroded away. A third huge waterlogged valley, Kipahulu, is making headway toward the summit even now from the east, between Kaupo and Ko’olau.
Kipahulu Valley sits in the heart of the rainiest part of the orthographic weather pattern, draining uncountable gallons of water a day and just as many uncountable pounds of rocks and soil. It is already a very deep, steep-sided valley, and rich with plant life (all those determined roots). All that remains to be eroded away between Kipahulu and the summit erosional valley/’crater’ is one thin wall—from the volcanic mountain perspective this wall is wafer-thin. A ‘waterfall’ of orthographic cloud and mist spills over it into the summit area almost every day. And, as that waferesque wall is water-saturated and heavily vegetated, it is already softening and diminishing. As is everything, everywhere that water has anything to say.