Marine terrasser
Kystskrænten
Frederikshavn er et sted der ikke er særligt kendt for geologiske fænomen. Men stadig findes det mange geologiske beviser for at denne lille by ikke altid har været som den er idag. Syd for byen findes nogle geologisk interessante kystskrænter. Bakken er en randmoræne, dannet under Weichsel-istiden, for mere information hvordan randmorænen dannedes, se gerne vores andre EarthCache "Pikkerbakken" (GC3Y3NW), kun tre og en halv kilometer væk.
Terrasserne
På den østlige siden af kystskrænten, kan man nemt se hvordan Yoldiahavet og Littorinahavet har påvirket området. 9700-8700 år siden dækkede Yoldiahavet det meste af Danmark, med nogle få områder undtaget. De deler af kystskrænten der er ca. 60 meter over havet idag, var upåvirkede af havets kraft. Det samme gælder derimod ikke området under Yoldiahavets kystlinie. Mellem 35 og 50 meter over dagens havsniveu har Yoldiahavet dannet en terasse med marint sand i overfalden, Yoldiafladen. I områdets sydlige del er den 300-400 meter bred og hælder 2-3% mod øst. Terrassen er let at se i disse deler af kystskrænten. Den bliver mindre og mindre bred længere mod nord. Ved Grønholt er det slet ikke muligt at se nogle spor.
I. Ishavsstadium: Det senglaciale Yoldiahav eroderer istidslandsskabet samtidigt som Yoldialer aflejres på havbunden. II. Stenalder-stadium: Langs Littorinahavets kyst dannes klinter i Yoldialeret. III. Nutids-stadium: Foran Littorinaskrænten findes nu en bræmme af marint forland. Yoldiafladen (2) er furet af erosion, mange af furerne eksisterede allerede i stadie II (ikke vist).
1. Istidslandskab, 2. Yoldiafladen (hævet havbund fra Senglacialtiden), 3. Littorinafladen (hævet havbund fra Stenalderen) 4. Yoldiahavets udjævnede kystskrænt, 5. Littorinahavets furede kystskrænt, 6. Nutidens kystlinie.
A: Istidsaflejringer, B: Yoldiahavets afleringer, C: Littorinahavets og yngre aflejringer.
Illustration: Naturstyrelsen Danmark (A. Schou, 1969)
Yoldiafladen afsluttes af en skrænt, Littorinaskrænten, der er cirka 15-20 meter høj (mellem ca 15-35 meter over dagens havsniveu). Littorinahavet eksisterede under Stenalderen (5500-2000 år siden), i denne tid gik havet fra at være brakt til salt. Mellem denne skrænt og dagens kystline finder man den postglaciale hævede havbund. Littorinafladen finder man i niveuet 5-15 meter over dagens havsniveu. Denne flade er cirka en kilometer bred ved områdets sydlige deler og omkring 150 meter bred ved Grønholt. Fladen består fortrinsvis af marint sand der er overlejret af flyvesand. Flyvesandet skjuler delvist et system af strandvolde fra Littorinatiden, der går i et system fra nord til syd.
Fra 5 metersniveuet ud til den nuværende kysten findes en zone med sandede strandenge. De er dannet for omkring 2000-3000 år siden. Ved 5-7 meter over dagens havsniveu kan man også finde et svagt terrænhak. Det er grænsen for den gamle Bronzealderskysten.
Pladsen
For at komme til pladsen (som er en lille rutte) kan du køre bil eller cykle. Men hvis du vil cykle, observer at du skal cykle 80 vertikale meter op for en ganske stejl bakke. Man kan gå hvis man vil, men då får man gå en ganske lang strække. For at kunne opleve terrasserne fuldt ud rekommenderer vi at du kører/cykler/går hele ruten til/fra Øksnebjerg (se waypoint) til/fra Haldbjerg (se waypoint). Ved topppen kan man nyde af en dejlig udsigt. Rutten går gennem en lille dal, der er skabt gennem erosion fra vandet. Derfor findes det forskelligheder fra tekstens højdeinformation.
Spørgsmålene
For at du skal få logge cachen online, skal du besvare følgende spørgsmål og sende svarene med e-mail til kajoluan@gmail.com. Du er ikke nødt til at vente på godkendelse fra os. Hvis svarene er fejl, vil vi kontakte dig. Hvis du ikke sender noget e-mail, vil din logning slettes.
1. Når du ser ud over landskabet fra "toppen"-koordinaterne, skal du tænke over hvordan du synes at landskabet ville set ud, hvis Yolida- og Littorinahavet aldrig havde eksisteret? Hvis de to havene ikke havde påvirket bakken, hvilke ville konsekvenserne være for beboerne? Send mig dine teorier.
2. Ser du hvor skrænterne begynder? Send koordinater for hvor du syner at Yoldiafladen slutter og Littorinaskrænten begynder. Hvor langt er det mellem skrænterne?
Du får meget gerne vedhefte et billede til din log online, men det er valgfrit. Skriv ikke svarene i din log!
English
Introduction
Frederikshavn isn't really a place known for it's geological phenomenas. But still there are a lot of geological proof for the fact that this little village hasn't always looked it does today. South of this village there are some geologically interesting "coastal slopes" (kystskrænter). These slopes are actually terminal moraines, formed during the latest ice age (Weichsel, or Devensian as it's called in the UK). For more information on how the terminal moraine was created, you can visit our nearby EarthCache "Pikkerbakken" (GC3Y3NW), regarding that subject.
The Terraces
On the eastern side of the coastal cliff, you can easily see how the Yoldia and Littorina Sea has 
affected the area. 9700-8700 years ago, in the late glacial period, Yoldia Sea covered most of Denmark, only a few places excepted. The parts of this coastal slope that are 60 metres above current sea level, were not affected by the force from the sea. The same can not be said about the parts below the old Yoldia seas costal line at 60 metres. Between 35 and 50 metres above todays sea level, the Yoldia Sea has created a marine terrace with marine sand. This plateau is about 300-400 metres wide in the south and is tilting approximately 2-3 degrees to the east. The terrace is easiest to see from these parts of the terminal moraine. At Grønholt in the north, it is no longer possible to see any traces of the terraces.
Information for the illustration in the Danish description: I. Ice sea stage: The late glacial Yoldia Sea is eroding the ice age landscape. Meanwhile, Yoldia mud is sedimented at the lake bed. II. Stoneage stage: Along the coast of the Littorina Sea, "dunes" are created in the Yoldia mud. III. Today: In front of the Littorina slope there is now a fringe of marine foreland. The Yoldia plateau (2) is furrowed by erosion. Many of the furrows were created in the II-stage, but that isn't shown in the II-illustration.
1. Ice age landscape, 2. The Yoldia plateau (risen sea bed from the late glacial period), 3. The Littorina plateau (risen sea bed from the Stone age), 4. The coastal slope smoothed by the Yoldia Sea, 5. The coastal slope furrowed by the Littorina Sea, 6. Today's coast line.
A: Ice age sedimentations, B: Yoldia Sea sedimentations, C: Littorina and younger sedimentations.
The Yoldia plateau is ended by a slope, the Yoldia slope, that is approximately 15-20 metres high (located between 15-35 metres above current sea level). The Littorina Sea existed during the Stone age (5500-2000 years ago) and in this period the sea was transformed from brackish to salt. Between this slope and today's coast line you find the postglacial risen sea bed. The Littorina plateau is found between approximately 5-15 metres above current sea level. This plateau is about a kilometre wide in the southern parts of the area and 150 metres in the north, at Grønholt. It is mostly made of marine sand, covered by drifting sand. This drifting sand partially covers a system of beach ridges stretching from north to the south.
From 5 metres above current sea level down to the coast line of today, there is an area of sandy beach meadows. They were created approximately 2000-3000 years ago. At 5-7 metres above current sea level, you can find a weak "bump" in the terrain. That is the old coast line of the Bronze age sea.
The place
To get to the coordinates you can either go by car or take a rather challenging bike ride up the slope (from the east). You can also come from the west via Understed and drive down hill. It is also possible to walk. The road is small, it is mostly made of gravel and it goes through a farm. To experience the terraces properly, we recommend you to drive/cycle/walk all the way up/down the route from the top (see waypoint) to the Littorina plateau waypoint. When you come to the valley (see waypoint), there is a question to answer.
The questions
To log this EarthCache online, you must answer the following questions and send the answers by e-mail to kajoluan@gmail.com. You don't have to wait for any approval from us. If the answers are incorrect, we will contact you. If you do not send any e-mail, your log will be deleted. It would be really nice if you would upload photos to your log, but it's entirely optional.
1. Look out over the landscape from the "toppen"-coordinates, how would it have looked like if the Yoldia- and Littorina Sea hadn't shaped it? If the seas never left any traces on the hill, what would the consequences have been for the inhabitants? Send me your theories.
2. Do you see where the Littorina slope begin? Send coordinates for where you think the Yoldia plateau ends and the Littorina slope begins.
Do not write the answers in your log!
When you are in the area, you can also visit our other EarthCache, Pikkerbakken. Just 3,5 kilometres away!
