Arizona-based scientist developing geologic map of Southeast Alaska

A position of nan Stikine River adjacent Wrangell and Petersburg. (Courtesy Cindi Lagoudakis)

A geologist who has studied Southeast Alaska’s rocks and minerals for decades is creating a caller geologic representation of nan region. That representation could person a wide scope of applications — from educating tourists, to helping prospectors find gold, to helping communities hole for landslides. 

Arizona-based geologist George Gehrels has studied Southeast Alaska’s rocks and minerals for complete 40 years. He stopped done Petersburg this summertime to do section investigation and show nan nationalist a small spot astir nan geologic history of nan world beneath their feet. He wrapped up his summertime investigation travel to rainy Southeast still tanned from nan Tucson sun, wherever he’s a earth science professor astatine nan University of Arizona. 

He’s been doing section investigation astir nan Coast Mountains since 1981 — going retired connected boats, carving up stone samples, and inspecting them pinch a mini magnifying glass. But Gehrels said each summertime he spends present is simply a small different. 

“Sometimes we person large groups of students pinch us, sometimes I’m retired pinch conscionable a workfellow and different professor aliases two,” he said. “Sometimes, I’ve been by myself pinch my canine — and past she’s nan geo-assistant for me!”

So, what makes nan region’s rocks truthful special? He said it starts pinch a process called “metamorphosis” — that’s erstwhile immense amounts of power and unit alteration nan statement of a rock. Gehrels describes Central Southeast stones successful position that almost sound tasty: crusty bits, flaky bits and what he calls nan “Crunch Zone.”

“Petersburg is benignant of successful nan large “Crunch Zone” of Southeast Alaska,” Gehrels said. “The plates are moving — North America, we know, has been moving westward for astir 200 cardinal years. As North America moves westward, it’s benignant of for illustration a bulldozer — aliases benignant of for illustration a snowplow — moving complete nan Pacific Ocean disconnected to nan west.”

Gehrels said Petersburg was correct smack successful nan way of that snowplow (or, bulldozer) astir 100 cardinal years ago, getting crammed up against different portion of nan continent astatine a velocity of astir 5 centimeters per twelvemonth — or, astir arsenic accelerated arsenic your fingernails and hairsbreadth tin grow. That intends Petersburg is portion of nan captious bound wherever onshore was deposited onto nan westbound seashore of North America. Gehrels said each that activity and metamorphosis produced immoderate beautiful cool rocks.

“Many Petersburg group cognize astir Garnet Ledge down by Wrangell,” Gehrels said. “Those garnets location are a consequence of this collision. When nan rocks get metamorphosed, minerals turn for illustration garnet. So, those are world-class.”

That’s each to opportunity that Wrangell’s garnets are world-class. Gehrels said nan aforesaid metamorphic arena formed nan humor reddish crystals that tin beryllium picked retired of nan hillsides successful neighboring Petersburg. But those garnets didn’t get basking capable successful nan statement process to beryllium arsenic bully arsenic Wrangell’s — they person much impurities. 

Gehrels said nan continental “Crunch Zone” produced immoderate of nan different rocks that qualify Central Southeast — there’s tons of sparkly schist and stripey gneiss and coarse quartzite. 

But there’s much to his investigation than conscionable cataloging cool rocks. Gehrels is gearing up to nutrient a geologic representation of nan area pinch immoderate scientists pinch nan Alaska State Survey. He said that representation could beryllium useful for group who mightiness want to extract definite minerals — for illustration golden — from nan area. Or, it could thief circuit guides explicate nan geological value of nan scenery to visitors. 

“Tourism is simply a immense portion of nan system successful Southeast Alaska correct now,” Gehrels said. “The group connected nan circuit ships, possibly they don’t recognize it, but 1 of nan main reasons they travel present is because of geology. It’s fabulous, it’s what controls our landscape. Tracy Arm, you know, 1 of nan astir beautiful places connected nan satellite — it owes its beauty successful ample portion to nan geology.”

But, moreover much importantly, nan accusation they’re gathering for nan representation could besides thief group measure nan stableness of nan slopes astir them, to protect their communities from disaster — for illustration erstwhile Wrangell knowledgeable a deadly landslide last fall. 

“That’s a cardinal taxable present successful nan Wrangell-Petersburg area correct now, aft nan large landslide,” Gehrels said. “And each of that benignant of depends connected knowing a small spot astir nan bedrock earth science successful Southeast Alaska. So that’s what we’re trying to do.”

He said his squad is processing an interactive integer map, wherever users tin zoom successful and out, truthful they tin spot nan level of item they want — benignant of for illustration Google Maps. But he said he’ll still people retired a fewer old-fashioned insubstantial versions — conscionable because he likes them. He expects it’ll astir apt return his squad a twelvemonth to decorativeness nan map, aft which, it will beryllium disposable to nan public.