Homer Alaska - News

Story last updated at 5:25 PM on Wednesday, September 26, 2012

KBRR investigates how landscape is being changed



By Carmen Field
Kachemak Bay Research Reserve


 

Photo provided by Kachemak Bay Research Reserve

This Continuously Operating Reference Station, or CORS, in Peterson Bay is a set of vertically and horizontally stable instruments that provide continuous, precise GPS measurements.

Although our beaches, bluffs, mountains and glaciers appear to remain the same from day to day or week to week, there's a lot going on under our feet in Kachemak Bay. While we fish, drive, shop and cook, the earth's crust is moving — pushing sideways toward cracks or trenches and thrusting upward.

We can't sense these geologic changes, but modern technology is helping local scientists and folks who work along or manage our coastline understand what's happening below us.

Fueled by a series of newspaper articles about coastal uplift from melting glaciers in Southeast Alaska and personal observations of change in our region, community leaders in Homer approached the Kachemak Bay Research Reserve, or KBRR, a few years ago in search of information.

With our town's dependence on local, nearshore fisheries for food and safe harbor infrastructure for transportation, there was a need to understand the implications that coastal uplift and sea level rise have for coastal erosion patterns, infrastructure construction and protection, planning, zoning, local food resources and public safety.

In 2011, KBRR subsequently received funding for and embarked on a unique investigation into how our landscape is being changed by undetectable, conflicting forces of nature. KBRR scientists — working with Alaska and Outside colleagues, local stakeholders and volunteer monitors — are trying to learn more about the relationships between coastal uplift, glacial melt and sea level rise by monitoring the impacts of these processes on biological communities and by assessing the rate of vertical changes in the coastal landscape encircling Kachemak Bay.

Sea level rise is caused by the expansion of sea water as it warms up in response to climate change and the widespread melting of land ice. To understand what that means locally, we also need to know how the land is changing. If our land is rising — more on that in a moment — and sea level also is rising, will the ground we live on outpace the encroaching ocean and avoid the projected fate of low-lying, coastal communities around the globe? Or will our shoreline be inundated and eroded by marine waters rising faster than the land?

Definitive answers to those questions are not yet known; however, it appears that — at least in the short term — coastal uplift may outpace sea level rise here.

By combining collected sea level data with predictive models, research agencies and institutions have determined that the pace of global sea level rise to currently be about 3.3 millimeters (.1 inch) per year. And data collected locally on the movement of bedrock indicates that the earth's crust in our region is uplifting at a rate of about 10 millimeters (.4 inch) per year.

That might seem to bode well for maintaining our current ways of life, but there are still many missing pieces in the puzzle of how natural forces shape our landscape. For instance, uplift of our salt marshes, the Homer Spit, and other unconsolidated substrates is not yet fully understood.

Locally, the powerful 1964 earthquake still plays a role in the tectonic processes (subsidence and rebound) affecting our land and is coupled with isostatic readjustment (often called "glacial rebound") occurring because of rapidly melting glaciers reducing the weight placed on the earth's surface.

This study will build upon existing coastal processes research conducted by the University of Alaska, Fairbanks and KBRR to provide a more accurate estimation of the relative sea level change (which incorporates rates of land and sea level change) throughout the bay.

KBRR scientists are collecting data on the rate and direction of crustal movements in Kachemak Bay using two methods. The first — called Continuously Operating Reference Stations, or CORS — are a set of vertically and horizontally stable instruments that provide continuous, very precise GPS measurements.

Five CORS sites have been established for this project at Voznesenka, McNeil Canyon, the Homer Spit, Beluga Slough and Peterson Bay. There also are two permanent CORS sites at Bradley Lake and Seldovia.

The second method for measuring land movement — "permanent benchmark stations" — is an array of sensitive GPS units, each placed with a large tripod on bedrock or over soft sediment.

At the soft-sediment sites, creating stable benchmarks is more difficult. Steel rods are pounded into the soft ground to a "point of refusal' to create a benchmark site. In the four salt marshes being studied, depths that the metal rods have been driven to at these stations in Kachemak Bay range from 3.7 to 42.7 meters, or 12 to 140 feet.

We as individuals don't perceive changes in the elevation of the land below us, but this 3-year project — which will include a final report summarizing land and sea level changes that are affecting Kachemak Bay — will certainly shed light on motion along and under our ocean. It also will provide valuable information to be used in local community planning.

For more information on this study or other research being conducted in Kachemak Bay, contact KBRR Research Coordinator Angie Doroff at 226-4654 or angela.doroff@alaska.gov or visit www.adfg.alaska.gov/index.cfm?adfg=kbrr_researchCollaborative.home.

Carmen Field is a marine science educator and naturalist at the Kachemak Bay Research Reserve.

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